RADIATION PROTECTION IN DENTISTRY AND … radiological practices. 12 ... 16 Report No. 145,...

NCRP DRAFT SC 4-5 REPORT

RADIATION PROTECTION IN DENTISTRY AND ORAL

AND MAXILLOFACIAL IMAGING

March 16, 2016

Note: Copyright permission is being sought for the figures and tables requiring such permission prior to

their use in the final NCRP publication.

National Council on Radiation Protection and Measurements

7910 Woodmont Avenue, Suite 400, Bethesda, Maryland 20814

NCRP SC 4-5 Draft March 16, 2016

2

Preface 1

2

No exposure to x rays can be considered completely free of risk, so the use of radiation by 3

dentists and their assistants implies a responsibility to ensure appropriate protection. The Report 4

provides radiation protection guidance for the use of x rays in dental practice including the use of 5

intraoral imaging, cone beam computed tomography, digital imaging radiation protection 6

devices, and hand held x-ray systems. 7

8

The aim of the Report is to provide a practical radiation protection guide for dentists and 9

their assistants. Information is presented in a clear and comprehensive format focusing on dental 10

radiological practices. 11

12

This Report is dedicated to the memory of S. Julian Gibbs, DDS, PhD, former 13

Professor of Radiology and Radiological Sciences at Vanderbilt University. Dr. 14

Gibbs was the Co-Chair of Scientific Committee 91, that was responsible for NCRP 15

Report No. 145, Radiation Protection in Dentistry, and he served as a member of the Council for 16

many years. His research interests focused on radiation doses from medical and dental radiologic 17

procedures, and he was a pioneer in applying computational techniques to studies of radiation 18

dose distribution to critical organs. He was a true scholar and humanitarian, and was an 19

inspiration and beloved mentor to dentists who pursued careers in the radiation sciences. 20

21

This Report supersedes NCRP Report No. 145, Radiation Protection in Dentistry, which 22

was issued in December 2003. This Report was prepared by Scientific Committee 4-5 on 23

Radiation Protection in Dentistry. Serving on Scientific Committee 4-5 were: 24

25

Co-Chairs 26

27

Alan G. Lurie

University of Connecticut

School of Dental Medicine

Farmington, Connecticut

Mel L. Kantor

University of Wisconsin-Eau Claire

Institute for Health Sciences

Eau Claire, Wisconsin


3

Members 28

29

Mansur Ahmad

University of Minnesota School of Dentistry

Minneapolis, MN

Veeratrishul Allareddy

University of Iowa College of Dentistry

Iowa City, Iowa

John B. Ludlow

University of North Carolina, School of

Dentistry

Chapel Hill, North Carolina

Edwin T. Parks

Indiana University School of Dentistry

Indianapolis, Indiana

Eleonore D. Paunovich

Veterans Health Administration

San Antonio Texas

Robert J. Pizzutiello

Landauer Medical Physics

Victor, New York

Robert A. Sauer

Food and Drug Administration

Center for Devices and Radiological Health

Silver Spring, Maryland

David C. Spelic




30

31

Consultants 32

33

Edwin M. Leidholdt, Jr.

Veterans Health Administration

Mare Island, California

William Doss McDavid

University of Texas Health Science Center at

San Antonio

San Antonia, Texas

Donald L. Miller




Madan Rehani

Harvard Medical School and

Massachusetts General Hospital

Boston, Massachusetts

34

35


4

NCRP Secretariat 36

37

Joel E. Gray, Staff Consultant 38

Cindy L. O’Brien, Managing Editor 39

Laura J. Atwell, Office Manager 40

James R. Cassata, Executive Director, 2014 41

David E. Smith, Executive Director, 2014 – 2016 42

43

The Council wishes to express its appreciation to the Committee members for the time and 44

effort devoted to the preparation of this Report, and to the following organizations for providing 45

financial support during its preparation: 46

47

American Academy of Oral and Maxillofacial Radiology 48

American Association of Physicists in Medicine 49

American Board of Radiology Foundation 50

American Dental Education Association 51

Food and Drug Administration, Center for Devices and Radiological Health 52

53

John D. Boice, Jr. 54

President 55

56


5

Contents 57

58

1. Executive Summary ....................................................................................................................... 13 59

1.1 General ....................................................................................................................................... 13 60

1.1.1 Purpose of the Report ....................................................................................................... 13 61

1.1.2 The Most Significant Methods to Minimize Radiation Dose, and Maximize Image 62

Quality and Diagnostic Efficacy ...................................................................................... 14 63

1.1.3 Quality Assurance of Radiology in the Dental Office ...................................................... 15 64

1.1.4 Education and Training .................................................................................................... 15 65

66

2. Introduction ..................................................................................................................................... 28 67

2.1 Purpose ....................................................................................................................................... 29 68

2.2 Scope .......................................................................................................................................... 29 69

2.3 Radiation Protection Philosophy ................................................................................................ 30 70

71

3. General Considerations .................................................................................................................. 34 72

3.1 Dose Limits ................................................................................................................................ 34 73

3.2 Role of Dental Personnel in Radiation Protection ..................................................................... 39 74

3.2.1The Dentist ....................................................................................................................... 40 75

3.2.2 Auxiliary Personnel .......................................................................................................... 41 76

3.2.3 The Qualified Expert ........................................................................................................ 41 77

3.3 Electronic Image Data Management .......................................................................................... 43 78

79

4. Radiation Protection in Dental Facilities ..................................................................................... 45 80

4.1 General Considerations ............................................................................................................... 45 81

4.1.1 Shielding Design ................................................................................................................. 46 82

4.1.2 Equipment Performance Evaluations and Radiation Protection Surveys ........................... 48 83

4.1.3 Signage ................................................................................................................................ 50 84

4.2 Diagnostic Reference Levels and Achievable Doses .................................................................. 50 85

4.3 Optimization of Image Quality and Patient Dose. General Principles ........................................ 53 86

4.4 Protection of the Patient .............................................................................................................. 55 87

4.4.1 Selection Criteria Examination Type and Frequency ........................................................ 55 88

4.4.1.1 Symptomatic Patients ............................................................................................. 56 89

4.4.1.2 Asymptomatic Patients .......................................................................................... 56 90


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4.4.1.3 Administrative Radiographs .................................................................................. 57 91

4.4.2 X-Ray Machines ............................................................................................................... 57 92

4.4.3 Examinations and Procedures ........................................................................................... 58 93

4.4.3.1 Intraoral Radiography ........................................................................................... 58 94

4.4.3.2 Panoramic Radiography ........................................................................................ 58 95

4.4.3.3 Cephalometric Radiography ................................................................................. 58 96

4.4.3.4 Fluoroscopy ........................................................................................................... 59 97

4.4.3.5 Cone Beam Computed Tomography ..................................................................... 59 98

4.4.4 Image Viewing Environment ............................................................................................ 60 99

4.4.4.1 Viewing Conditions for Digital Images ................................................................ 61 100

4.4.5 Use of Radiation Protective Aprons .................................................................................. 62 101

4.4.5.1 Use of Thyroid Collars .......................................................................................... 63 102

4.4.5.2 Maintenance of Protective Aprons and Thyroid Shields ...................................... 63 103

4.4.6 Special Considerations for Pediatric Imaging ................................................................... 64 104

4.5 Protection of the Operator .......................................................................................................... 65 105

4.5.1 Shielding Design ............................................................................................................... 65 106

4.5.2 Barriers .............................................................................................................................. 65 107

4.5.3 Distance ............................................................................................................................. 66 108

4.5.4 Position of Operator .......................................................................................................... 66 109

4.5.5 Personal Dosimeters .......................................................................................................... 68 110

4.6 Protection of the Public .............................................................................................................. 69 111

112

5. Quality Assurance and Quality Control ....................................................................................... 71 113

5.1 Image Quality and Patient Dose Optimization ............................................................................ 70 114

5.1.1 Image Quality ..................................................................................................................... 71 115

5.1.2 Patient Dose ....................................................................................................................... 73 116

5.1.3 Technique Charts ............................................................................................................... 73 117

5.2 Quality Control ........................................................................................................................... 74 118

5.2.1 Radiation Measurements of X-Ray Producing Dental Diagnostic Equipment .................. 75 119

5.2.2 Phantoms for Quality Control and Dose Measurements .................................................... 76 120

5.2.3 Quality Control for Film Imaging ...................................................................................... 76 121

5.2.4 Quality Control for Digital Image Receptors ..................................................................... 78 122

5.2.5 Quality Control for CBCT ................................................................................................. 81 123

5.2.6 Quality Control for Image Displays ................................................................................... 84 124


7

5.2.7 Quality Control Tests and Frequency for Digital Radiography ......................................... 84 125

5.3 Infection Control ........................................................................................................................ 87 126

127

6. Image Receptors .............................................................................................................................. 88 128

6.1 Direct Exposure X-ray Film ........................................................................................................ 88 129

6.1.1 General Information ........................................................................................................... 88 130

6.1.2 Equipment and Facilities .................................................................................................... 90 131

6.1.2.1 Darkroom Fog ........................................................................................................ 90 132

6.1.2.2 Storage of Radiographic Film ................................................................................ 91 133

6.1.2.3 Film Processors ...................................................................................................... 91 134

6.2 Screen-Film Systems ................................................................................................................. 92 135

6.2.1 General Information .......................................................................................................... 92 136

6.2.2 Equipment and Facilities ................................................................................................... 93 137

6.2.2.1 Care of Screen-Film Systems for Film-Based Cephalometric and Film-Based 138

Panoramic Imaging ............................................................................................... 93 139

6.2.2.2 Screen-Film Speed Recommendation ................................................................... 93 140

6.3 Digital Imaging Systems ............................................................................................................ 94 141

6.3.1 General Information .......................................................................................................... 94 142

6.3.1.1 Proportion of Digital versus Film, Proportion of PSP versus CMOS-CCD ......... 94 143

6.3.1.2 Advantages of Digital Imaging Compared to Film Imaging ................................. 94 144

6.3.1.3 Potential for Dose Reductions for PSP and DR Compared with Film .................. 95 145

6.3.1.4 Disadvantages and Challenges of Digital Imaging ............................................... 98 146

6.3.2 Equipment and Facilities ................................................................................................. 100 147

6.3.2.1 PSP Plates ............................................................................................................ 100 148

6.3.2.2 Solid State Receptors ........................................................................................... 105 149

6.3.2.3 Converting from Film to Digital Imaging—Potential Dose Reduction ............... 107 150

6.3.2.4 Technique Charts ................................................................................................. 107 151

6.3.2.5 Clinical Image Display Monitors for Digital Imaging ......................................... 107 152

153

7. Intraoral Dental Imaging ............................................................................................................. 110 154

7.1 General Considerations ............................................................................................................. 110 155

7.1.1 Beam Energy .................................................................................................................... 110 156

7.1.2 Position-Indicating Devices ............................................................................................. 110 157

7.1.3 Rectangular Collimation .................................................................................................. 111 158


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7.1.4 Patient Restraint ............................................................................................................... 116 159

7.1.5 Diagnostic Reference Levels and Achievable Doses ...................................................... 116 160

7.1.6 Best Practices .................................................................................................................. 117 161

7.1.7 FDA Clearance of Dental Imaging Equipment ............................................................... 117 162

7.2 Conventional X-Ray Systems(Wall Mounted and Portable) .................................................. 119 163

7.2.1 General Information ....................................................................................................... 119 164

7.2.2 Equipment and Facilities ................................................................................................ 119 165

7.2.2.1 Protection of the Operator and Shielding .......................................................... 120 166

7.2.2.2 Tube Head Positional Stability .......................................................................... 120 167

7.2.2.3 Positioning-Indicating Devices ......................................................................... 120 168

7.2.2.4 Rectangular Collimation ................................................................................... 120 169

7.3 Hand-Held X-Ray Systems .................................................................................................... 121 170

7.3.1 General Information ...................................................................................................... 121 171

7.3.1.1 Advantages of Hand-Held X-Ray Units ........................................................... 122 172

7.3.1.2 Disadvantages of Hand-Held X-Ray Units ....................................................... 122 173

7.3.1.3 Safety Issues with Improper Handling of Hand-Held X-Ray Equipment ........ 124 174

7.3.1.4 Exception to “Never Hold the X-Ray Tube” ................................................... 126 175

7.3.2 Equipment ........................................................................................................................ 127 176

7.3.2.1 Backscatter Shield ................................................................................................ 127 177

7.3.2.2 Leakage Radiation ................................................................................................ 128 178

7.3.2.3 Radiation Protective Equipment and Personal Radiation Monitoring ................. 128 179

7.3.2.4 Appropriate Use of Hand-Held X-Ray Machines in Dental Offices 180

Comparison to European Recommendations ....................................................... 131 181

7.3.3 Position-Indicating Devices .............................................................................................. 131 182

7.3.4 Rectangular Collimation ................................................................................................... 131 183

184

8. Extraoral Dental Imaging ............................................................................................................ 133 185

8.1 Panoramic ................................................................................................................................. 133 186

8.1.1 General Information ......................................................................................................... 133 187

8.1.1.1 Diagnostic Reference Levels and Achievable Doses ........................................... 133 188

8.1.1.2 Bitewings from Digital Panoramic Machines ...................................................... 134 189

8.1.2 Equipment and Facilities .................................................................................................. 134 190

8.2 Cephalometric ........................................................................................................................... 136 191

8.2.1 General Information ......................................................................................................... 136 192


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8.2.1.1 Diagnostic Reference Levels and Achievable Doses ........................................... 136 193

8.2.2 Equipment and Facilities .................................................................................................. 136 194

195

9. Cone-Beam Computed Tomography .......................................................................................... 138 196

9.1 General Information .................................................................................................................. 138 197

9.1.1 Dose Comparisons for CBCT and MDCT Machines ...................................................... 140 198

9.1.2 Use of Simulated Bitewing. Panoramic and Cephalometric Views from 199

CBCT Data ....................................................................................................................... 145 200

9.1.3 Number of CBCTs in the United States and Growth Rate ............................................... 145 201

9.1.4 Efforts Regarding CBCT in Europe—SEDENTEXCT and Evidence-Based 202

Guidelines ........................................................................................................................ 147 203

9.1.5 Patient Selection Criteria for CBCT ................................................................................ 148 204

9.1.5.1 Implants ................................................................................................................ 148 205

9.1.5.2 Oral and Maxillofacial Surgery ............................................................................ 149 206

9.1.5.3 Periodontal Indications ........................................................................................ 150 207

9.1.5.4 Endodontic Indications ........................................................................................ 151 208

9.1.5.5 Temporomandibular Joint Indications ................................................................. 151 209

9.1.5.6 Caries Diagnosis Indications ............................................................................... 151 210

9.1.5.7 Sinonasal Evaluation Indications ........................................................................ 151 211

9.1.5.8 Craniofacial Disorders Indications ...................................................................... 152 212

9.1.5.9 Orthodontics ........................................................................................................ 152 213

9.1.5.10 Obstructive Sleep Apnea ................................................................................... 153 214

9.2 Equipment and Facilities ....................................................................................................... 153 215

9.2.1 Radiation Dose Structured Report Equivalent Needed for CBCT .................................. 155 216

9.2.2 Advantages of Pulsed Systems over Continuous Radiation Exposure Systems ............. 156 217

9.2.3 Advantages of 180 Degree Scan versus 360 Degree Scans ............................................ 157 218

9.2.4 Location of Equipment and Requirements for Shielding ................................................ 157 219

220

10. Administrative and Education ................................................................................................... 158 221

10.1 Administrative and Regulatory Considerations ..................................................................... 158 222

10.1.1 Compliance with FDA Medical Device Regulations and Electronic Product 223

Radiation Control Performance Standards .................................................................. 158 224

10.1.2 General Considerations ............................................................................................... 159 225

10.1.3 Hand-Held X-ray Devices ........................................................................................... 161 226


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10.1.4 CBCT Units ................................................................................................................ 161 227

10.1.4.1 Advanced Diagnostic Imaging Accreditation ............................................... 163 228

10.2 Education and Training .......................................................................................................... 164 229

10.2.1 Digital Imaging ........................................................................................................... 166 230

10.2.2 Hand-held Imaging Systems ....................................................................................... 166 231

10.2.2.1 Practitioner—Additional Safety Concerns .................................................... 166 232

10.2.2.2 Operator Training .......................................................................................... 166 233

10.2.2.3 Qualified Expert—Required Information ..................................................... 167 234

10.2.3 CBCT Imaging Systems .............................................................................................. 167 235

10.2.3.1 Training for Practitioners .............................................................................. 167 236

10.2.3.2 Training for Operators .................................................................................. 169 237

10.2.3.3 Training for Qualified Experts ...................................................................... 169 238

10.2.3.4 Continuing Education for Practitioners, Operators, and Qualified Experts .. 169 239

240

11. Summary and Conclusions ........................................................................................................ 171 241

242

Appendix A. Quality Control for Film Processing ......................................................................... 173 243

A.1 Five Basic Rules for Film Processing .................................................................................... 173 244

A.2 Quality Control ..................................................................................................................... 174 245

A.2.1 Sensitometry and Densitometry .................................................................................... 174 246

A.2.2 Dental Radiographic Quality Control ........................................................................... 174 247

A.2.3.1 Dental Radiographic Quality Control Device .................................................. 175 248

A.2.3.2 Aluminum Step Wedge .................................................................................... 175 249

A.2.3.3 Lead Foil Step Wedge ...................................................................................... 175 250

A.2.3.4 Reference Film ................................................................................................. 175 251

252

Appendix B. Quality Control for Digital Imaging Systems ........................................................... 177 253

B.1 Quality Control of Digital Intraoral Systems .......................................................................... 177 254

B.1.1 The Display .................................................................................................................... 177 255

B.1.2 Quality Control Phantoms .............................................................................................. 178 256

B.1.3 Baseline Exposure Assessment ...................................................................................... 178 257

B.1.4 Baseline Image ............................................................................................................... 178 258

B.1.5 Follow-up Images ........................................................................................................... 179 259

B.1.6 Record Keeping .............................................................................................................. 179 260


11

261

Appendix C. Historical Aspects of Digital Imaging ...................................................................... 181 262

263

Appendix D. Shielding Design for Dental Facilities ...................................................................... 185 264

D.1 General Shielding Principles ................................................................................................... 186 265

D.2 Shielding for Primary and Secondary Radiation ..................................................................... 188 266

D.3 Shielding Principles ................................................................................................................ 191 267

D.4 Occupancy Factors, Use Factors, and Workloads ................................................................... 191 268

D.4.1 Occupancy Factors ........................................................................................................ 191 269

D.4.2 Use Factors .................................................................................................................... 191 270

D.4.3 Workloads ..................................................................................................................... 191 271

D.5 Summary ................................................................................................................................. 195 272

273

Appendix E. Dosimetry, Intraoral, and Panoramic Imaging ....................................................... 196 274

E.1 Patient Dosimetry .................................................................................................................... 196 275

E.2 Operator Dosimety .................................................................................................................. 200 276

277

Appendix F. Dosimetry for Multidetector-Multislice Imaging of 278

Dentomaxillofacial Areas ........................................................................................................... 202 279

280

Appendix G. Dosimetry for Dental Cone Beam CT Imaging ....................................................... 204 281

282

Appendix H. Dental X-Ray Evaluation by Qualified Expert ........................................................ 220 283

H.1 Radiation Safety ...................................................................................................................... 220 284

H.2 Evaluation of the Image Receptor and Dose ........................................................................... 221 285

H.3 Film Processing Conditions and Quality ................................................................................. 221 286

H.4 Evalutation of the X-Ray Generator and Output ..................................................................... 223 287

H.5 Evaluation of the Beam Collimation ....................................................................................... 223 288

H.6 Occupational Radiation Exposure Assessment ....................................................................... 223 289

290

Appendix I. Radiation Risk Assessment ......................................................................................... 225 291

I.1 Introduction ............................................................................................................................. 225 292

I.2 Definitions ................................................................................................................................. 226 293

I.2.1 Stochastic Effects .............................................................................................................. 226 294


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I.2.2 Deterministic Effects (Tissue Reactions) .......................................................................... 227 295

I.2.3 Dose Language .................................................................................................................. 227 296

I.3 Studies of Irradiated Human Populations ................................................................................... 228 297

I.3.1 Introductions ....................................................................................................................... 228 298

I.3.2 Atomic Bomb Survivor Lifetime Studies ........................................................................... 230 299

I.3.3 Children Irradiated for Tinea Capitis and Enlarged Thymus.............................................. 230 300

I.3.4 Females Receiving Fluoroscopy for Tuberculosis Treatment Follow-up ........................... 232 301

I.3.5 United Kingdom National Registry of Radiation Workers................................................. 232 302

I.3.6 2013 Australian CT Study of Electronic Medicare Data .................................................... 234 303

I.4 Effects of In Utero Exposure ...................................................................................................... 234 304

I.5 Effects on Children ..................................................................................................................... 234 305

I.5.1 Joint Commission Report (2011) ........................................................................................ 235 306

I.5.2 2012 U.K. Study of Head CT Scans in Children ................................................................ 235 307

I.6 Heritable Genetic Effects ............................................................................................................ 238 308

I.7 Risk from Traditional Oral and Maxillofacial Imaging: Intraoral, Panoramic, and 309

Cephalometric ........................................................................................................................... 238 310

I.8 Risk from CBCT Imaging .......................................................................................................... 239 311

I.9 Other Risks in Daily Living for Comparison.............................................................................. 239 312

313

Appendix J. Radiation Quantities and Units .................................................................................. 244 314

315

Abbreviations, Acronyms and Symbols .......................................................................................... 246 316

317

Glossary ............................................................................................................................................ 247 318

319

References ......................................................................................................................................... 262 320

321


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1. Executive Summary 322

323

1.1 General 324

325

Radiology in dentistry is omnipresent, as evidenced by the approximately one billion 326

intraoral images produced in the United States in 2014 to 2015 (Farris and Spelic, 2015). In the 327

15 y since the prior NCRP report, NCRP Report No. 145, Radiation Safety in Dentistry, three 328

innovations have found significant application throughout general and specialty dentistry: digital 329

acquisition of images, hand-held intraoral imaging devices, and cone-beam computed 330

tomography (CBCT). 331

332

Dentistry is unique in that most dentists in private practice are not only the treating clinician 333

but also both the radiologist and radiation safety officer in the office. Use of x-ray imaging in 334

dental practice, in particular digital imaging and CBCT, has increased steadily for decades and 335

we anticipate this trend to continue. Conversely, the average radiation exposure for individual 336

intraoral, panoramic and cephalometric images have decreased. However, the addition of CBCT 337

to dentistry, with the potential for use of inappropriate exposure parameters or inappropriate use, 338

along with persistence of round collimation and D-speed film for intraoral imaging, require 339

concerted, focused efforts towards optimization to achieve and maintain diagnostic quality 340

imaging at the lowest possible radiation dose [as low as reasonably achievable (ALARA) 341

principle]. 342

343

1.1.1 Purpose of the Report 344

345

The purpose of this report is to enhance radiation safety in dentistry and to reinforce 346

published, well-known dose-reduction methods that are not yet being widely applied in the day-347

to-day practice of dentistry. The technological advances since NCRP Report No. 145 (NCRP, 348

2003) require changing attitudes and practices of dentists because opportunities are now present 349

for decreasing radiation doses while improving diagnostic efficacy. This report updates the 350

material in NCRP Report No.145, adds new content on digital imaging, hand-held x-ray devices, 351


14

CBCT, and makes recommendations for reducing patient radiation doses and improving image 352

quality, all in the context of the ALARA principle. 353

354

1.1.2 The Most Significant Methods to Minimize Radiation Dose, and Maximize Image Quality 355

and Diagnostic Efficacy 356

357

Many of the recommendations in this report are grounded in the recommendations of NCRP 358

Report No. 145, and are recommendations that could be quickly and inexpensively employed in 359

today’s dental practice environment. They include: 360

361

Use selection criteria for every imaging examination. 362

Use the fastest imaging receptor possible for all intraoral and extraoral imaging. For 363

intraoral imaging use either ANSI F-speed film or digital receptors. Eliminate D-speed 364

film. 365

Use rectangular collimation for all intraoral imaging except where patient anatomy or 366

behavior does not allow its use. 367

Use thyroid collars for all intraoral imaging and extraoral imaging (panoramic and 368

cephalometric) where it does not interfere with the required diagnostic information on the 369

image. 370

Ensure technique factors or imaging protocols are optimized to produce adequate images 371

with the lowest dose to the patient. 372

Follow the film manufacturers’ guidelines for processing film. 373

374

Additionally, new recommendations pertaining to acquisition technical factors and 375

indications for use are provided for digital, hand-held, and CBCT imaging: 376

377

Employ appropriate selection criteria for obtaining CBCT images. 378

Acquire CBCT images using the smallest field of view and acquisition technical factors 379

that deliver the needed diagnostic information at the lowest possible radiation dose. 380

Use only x-ray units which have been cleared by the U.S. Food and Drug Administration 381

(FDA). This is especially true with hand-held, intraoral x-ray devices. 382


15

Embrace the efforts of Image Gently— be mindful of the greater sensitivity to radiation 383

damage in children, conduct imaging exams only when clinically warranted, and 384

downsize radiation doses accordingly, with consideration of the diagnostic requirements 385

of the imaging task. 386

387

1.1.3 Quality Assurance of Radiology in the Dental Office 388

389

The dentist, with the assistance of the qualified expert, must establish and implement 390

protocols and procedures for the safe and effective use of diagnostic radiology in the office. This 391

includes maintenance and optimization of dental imaging equipment and quality control of the 392

components of digital imaging systems. 393

394

1.1.4 Education and Training 395

396

Advances in imaging technology, especially with the rapidly increasing use of CBCT 397

imaging, require more education and training of dentists and staff in the safe and effective use of 398

such technologies. Such training is not within the expertise of salespersons and must be 399

conducted by trained professionals from the manufacturers and by qualified experts. 400

401

The following Table 1.2 lists all of the recommendations made in this report in the order in 402

which they appear in the subsequent chapters. The subsection in which each statement appears 403

and is discussed is noted in the right-hand column. The recommendations should not be read in 404

isolation. The reader should consult the indicated subsection for more complete explanations 405

and further information. 406

407

Two terms used in this Report have a special meaning as indicated by the use of italics. 408

409

1. Shall and shall not are used to indicate that adherence to the recommendation is 410

considered necessary to meet accepted standards of protection. 411

2. Should and should not are used to indicate a prudent practice to which exceptions may 412

occasionally be made in appropriate circumstances. 413


16

TABLE 1.2—Recommendations. 414

Number Recommendation Section

1 No individual worker shall receive an occupational effective dose in excess of

50 mSv in any 1 y.

3.1

2 The numerical value of the individual worker’s life-time occupational effective

dose shall be limited to 10 mSv times the value of his or her age in years.

Occupational equivalent doses shall not exceed 0.5 mSv in a month to the

embryo or fetus for pregnant individuals, once pregnancy is known.

3.1

3 Mean nonoccupational effective dose to frequently or continuously exposed

members of the public shall not exceed 1 mSv y-1 (excluding doses from

natural background and medical care); infrequently exposed members of the

public shall not be exposed to effective doses >5 mSv in any year.

3.1

4 The dentist (or, in some facilities, the designated radiation safety officer) shall

establish and periodically review a radiation protection program. The dentist

shall seek guidance of a qualified expert in this activity.

3.2.1

5 The dentist shall employ published. evidence-based selection criteria when

prescribing radiographs.

3.2.1

6 Radiological procedures shall be performed only by dentists or by legally

qualified and credentialed auxiliary personnel.

3.2.2

7 The qualified expert should provide guidance for the dentist or facility

designer in the layout and shielding design of new or renovated dental

facilities and when equipment is installed that will significantly increase the

air kerma incident on walls, floors, and ceilings.

3.2.3

8 The qualified expert shall provide guidance for the dentist regarding

establishment of radiation protection policies and procedures.

3.2.3


17

9 To avoid unnecessary repeat exposures due to lost images or redundant

examinations, the electronic image data management system shall provide for

secure storage, retrieval, and transmission of images.

3.3

10 All digital images acquired shall be retained in the patient’s electronic record. 3.3

11 All digital images should be backed up offsite electronically in a separate,

safe, and secure location at regular intervals.

3.3

12 The qualified expert should perform a pre-installation radiation shielding

design and plan review, to determine the proper location and composition of

barriers used to ensure radiation protection in new or renovated facilities, and

when equipment is installed that will significantly increase the air kerma

incident on walls, floors, and ceilings.

4.1.1

13 The qualified expert shall perform a post-installation radiation protection

survey to assure that radiation exposure levels in nearby public and controlled

areas are ALARA and below the limits established by the state or other local

agency with jurisdiction.

4.1.1

14 The qualified expert should assess each facility individually and document the

recommended shielding design in a written report.

4.1.1

15 The qualified expert should consider the cumulative radiation exposures

resulting from representative workloads in each modality when designing

radiation shielding for rooms in which there are multiple x-ray machines.

4.1.1

16 The facility shall establish administrative controls that assure no more than

one patient is in an x-ray room with multiple x-ray machines during any x-ray

exposure.

4.1.1

17 A qualified expert shall evaluate x-ray equipment to ensure that it is in

compliance with applicable governing laws and regulations.

4.1.2

18 All new dental x-ray installations shall have a radiation protection survey and

equipment performance evaluation carried out by, or under the direction of, a

qualified expert.

4.1.3


18

19 Equipment performance evaluations shall be performed by a qualified expert

at regular intervals thereafter, preferably at intervals not to exceed 4 y for

facilities only with intraoral, panoramic or cephalometric units. Facilities with

CBCT units shall be evaluated every 1 to 2 y.

4.1.3

20 Diagnostic Reference Levels and Achievable Doses should be developed for

dental CBCT imaging.

4.2

21 Each dental facility should record and track indicators of patient dose, such as

entrance air kerma and associated technique factors.

4.2

22 Each dental facility should compare its doses to DRLs and ADs. In particular,

where established methods exist, the qualified expert shall collect dose data

suitable for comparison with DRLs and ADs. These data and the results shall

be provided in the qualified experts report. For dental imaging systems that

provide dose metrics for patient examinations, the dentist or qualified expert

should periodically compare medians of these data for 10 clinical

examinations appropriate for this purpose with DRLs and ADs.

4.2

23 Organizations such as NCRP, U.S. Food and Drug Administration (FDA),

Conference of Radiation Control Program Directors (CRCPD), American

Academy of Oral and Maxillofacial Radiology (AAOMR), and American

Dental Association (ADA) should strive to provide DRLs and ADs for a

variety of dental examinations.

4.2

24 All radiological examinations shall be performed only on direct prescription of

the dentist, physician, or other individuals authorized by law or regulation.

4.4.1

25 Radiographic examinations shall be performed only when patient history and

physical examination, prior images, or laboratory findings indicate a

reasonable expectation of a health benefit to the patient.

4.4.1

26 For each new or referred patient, the dentist shall make a good faith attempt to

obtain previous, pertinent images prior to acquiring new patient images.

4.4.1


19

27 For symptomatic patients, the radiological examinations shall be limited to

those images required for diagnosis and treatment of current disease.

4.4.1.1

28 For asymptomatic patients, the extent of radiological examination of new

patients, and the frequency and extent for established patients, shall adhere to

current published, evidence based selection criteria.

4.4.1.2

29 Administrative use of radiation to provide information that is not necessary for

the treatment or diagnosis of the patient shall not be permitted.

4.4.1.3.

30 Students shall not be compelled or permitted to perform radiographic

exposures of humans solely for purposes of education.

4.4.1.3

31 Candidates shall not be compelled or permitted to perform radiographic

exposures of humans solely for purposes of licensure, credentialing or other

certification.

4.4.1.3

32 Personnel responsible for purchase and operation of dental x-ray equipment

shall ensure that such equipment meets or exceeds all applicable U.S. federal

government and state requirements and regulations. In addition, the equipment

should conform to current international standards for basic safety and essential

performance.

4.4.2

33 Fluoroscopy shall not be used for static imaging in dental radiography. If

fluoroscopy is used for dynamic imaging, the practices in NCRP Report No.

168 shall be followed.

4.4.3.4

34 Images shall be viewed in an environment adequate to ensure accurate

interpretation.

4.4.4

35 The use of radiation protective aprons on patients shall not be required if all

other recommendations in this Report are rigorously followed unless required

by state regulation. Otherwise, a radiation protective apron shall be used.

4.4.5

36 Thyroid shielding shall be provided for patients when it will not interfere with

the examination.

4.4.6


20

37 Protective aprons and thyroid shields should be hung or laid flat and never

folded, and manufacturer’s instructions should be followed. All protective

shields should be evaluated for damage (e.g., tears, folds, and cracks)

quarterly using visual and manual inspection.

4.4.7

38 Technique factors and selection criteria shall be appropriate to the age and size

of the patient.

4.4.8

39 Adequacy of facility shielding shall be determined by the qualified expert

whenever the average workload increases by a factor of two or more from the

initial design criteria.

4.5.1

40 Shielding designs for new offices with fixed x-ray equipment installations

shall provide protective barriers for the operator. The barriers shall be

constructed so operators can maintain visual contact and audible

communication with patients throughout the procedures.

4.5.2

41 The exposure switch should be mounted behind the protective barrier such

that the operator must remain behind the barrier during the exposure.

4.5.2

42 In the absence of a barrier in an existing facility, the operator shall remain at

least 2 m, but preferably 3 m, from the x-ray tube head during exposure. If the

2 m distance cannot be maintained, then a barrier shall be provided. This

recommendation does not apply to hand-held units with integral shields.

4.5.3

43 Provision of personal dosimeters for external exposure measurement should

be considered for workers who are likely to receive an annual effective dose in

excess of 1 mSv. Personal dosimeters shall be provided for declared pregnant

occupationally-exposed personnel.

4.5.5

44 For new or relocated equipment, the facilities shall provide personal

dosimeters for at least 1 y in order to determine and document the doses to

personnel.

4.5.5

45 The facility shall provide personal dosimeters for all new operators of hand-

held dental x-ray equipment for the first year of use.

4.5.5


21

46 In dental facilities using large, multi-patient open bay designs, a patient in

proximity to another patient being radiographed shall be treated as a member

of the public for radiation protection purposes.

4.6

47 When portable or hand-held x-ray machines are used, all individuals in the

area other than the patient and operator shall be protected as members of the

public.

4.6

48 New dental facilities shall be designed such that no individual member of the

public will receive an effective dose in excess of 1 mSv annually.

4.6

49 X-ray machines should provide a range of exposure times suitable for twice

the speed of the fastest available image receptors.

5.1.1

50 A suitable radiographic phantom shall be used to optimize radiation dose and

image quality, and for continuing quality control measurements.

5.2.2

51 Film processing quality shall be evaluated daily, before processing patient

films, for each film processor or manual processing system.

5.2.3

52 There shall be an infection control policy to protect staff and patients that

encompasses imaging equipment and procedures.

5.3

53 Imaging equipment and devices should be designed to facilitate standard

infection control precautions.

5.3

54 Image receptors of speeds slower than ANSI Speed Group E-F film shall not

be used for intraoral radiography, i.e., D-speed film shall not be used.

6.1.1

55 Each darkroom and daylight loader shall be evaluated for fog at initial

installation, and then at least quarterly and following change of room lighting

or darkroom safelight lamp or filter.

6.1.2.1

56 Film, including film in cassettes, shall not be exposed to excessive radiation

during the period it is in storage.

6.1.2.2


22

57 Film shall be processed with active, properly replenished chemicals and time-

temperature control, according to manufacturers’ recommendations.

6.1.2.3

58 Screen-film systems of speeds slower than ANSI 400 shall not be used for

panoramic or cephalometric imaging. Rare-earth systems shall be used.

6.2.2.2

59 The dental practice should enlist the assistance from a qualified expert to

ensure each new digital system is properly configured with regard to both

patient dose and image quality.

6.3.1.4

60 When converting from film to digital imaging, the facility shall make proper

exposure technique (time) adjustments, commensurate with the digital imaging

system.

6.3.2.4

61 The operating potentials of intraoral dental x-ray units shall not be <60 kVp

and should not be >80 kVp.

7.1.1

62 Position-indicating devices shall be open-ended devices and should provide

attenuation of scattered radiation arising from the collimator or filter.

7.1.2

63 Source-to-skin distance for intraoral radiography shall be at least 20 cm and

preferably should be at least 30 cm.

7.1.2

64 Rectangular collimation of the x-ray beam shall be used routinely for

periapical and bitewing radiography, and should be used for occlusal

radiography when imaging children with size 2 receptors

7.1.3

65 Occupationally-exposed personnel should not routinely restrain uncooperative

patients and shall not hold the image receptor in place during an x-ray

exposure.

7.1.4

66 Comforters and caregivers who restrain patients or hold image receptors

during exposure shall be provided with shielding, e.g., radiation protective

aprons , and should hold the film holding device. No unshielded body part of

the person restraining the patient shall be in the primary beam.

7.1.4


23

67 The stand of a mobile unit shall provide adequate support to the x-ray tube

during travel and when the articulating arm is fully extended, and during x-ray

exposure. The wheels or the casters shall be equipped with a foot brake to

prevent motion of the unit during exposure.

7.2.2

68 Only the patient and operator shall be in the area during an exposure unless

special circumstances do not allow this.

7.2.2

69 The tube head shall achieve a stable position, free of drift and oscillation,

within 1 s after its release at the desired operating position. Drift during that 1

s shall be no greater than 0.5 cm.

7.2.2.2

70 Operators of hand-held x-ray equipment shall have the physical ability to hold

the system in place for multiple exposures.

7.3.1.3

71 Manufacturers should provide a training program for users of hand-held

equipment to emphasize the appropriate safety and positioning aspects of their

unit.

7.3.1.3

72 Operators shall store hand-held x-ray equipment such that it is not accessible

to members of the public when not in use.

7.3.1.3

73 Manufacturers of hand-held x-ray equipment shall incorporate either hardware

or software interlocks on their devices to prevent unauthorized use. Hardware

interlocks may include physical keys or locks necessary for operation while

software interlocks may include password restrictions.

7.3.1.3

74 Instructions supplied with hand-held x-ray equipment shall include

identification of the areas in which it is safe for the operator to stand during

exposures based on the specific protective shielding in the device design.

7.3.1.4

75 Hand-held x-ray devices shall include a clear, external, nonremovable,

radiation protection shield containing a minimum of 0.25 mm lead equivalence

between the operator and the patient to protect the operator from backscatter

radiation.

7.3.2.1


24

76 The operator of a hand-held x-ray unit shall not be required to wear a personal

radiation protective garment.

7.3.2.3

77 Rectangular collimation shall be used with hand-held devices whenever

possible.

7.3.4

78 The x-ray beam for rotational panoramic tomography shall be collimated such

that its vertical dimension is no greater than that required to expose the area of

clinical interest and shall not exceed the size of the image receptor.

8.1.2

79 The fastest imaging system consistent with the imaging task (equal to or

greater than ANSI 400 speed, or digital) shall be used for all panoramic

radiographic projections.

8.1.2

80 Panoramic machines shall be on a dedicated electrical circuit. 8.1.2

81 The fastest imaging system consistent with the imaging task (ANSI 400 speed

or greater, or digital) shall be used for all cephalometric radiographic

projections.

8.2.2

82 X-ray equipment for cephalometric radiography shall provide for asymmetric

collimation to limit the beam to the area of clinical interest.

8.2.2

83 Filters for imaging the soft tissues of the facial profile together with the facial

skeleton shall be placed between the patient and at the x-ray source rather than

at the image receptor.

8.2.2

84 CBCT should be used for cross sectional imaging as an alternative to

conventional computed tomography when the radiation dose of CBCT is lower

and the diagnostic yield is at least comparable.

9.1.1

85 CBCT examinations shall use the smallest field of view (FOV) and technique

factors that provide the lowest dose commensurate with the clinical purpose.

9.1.1

86 CBCT examinations shall not be obtained solely for the purpose of producing

simulated bitewing, panoramic, or cephalometric images.

9.1.2


25

87 CBCT shall not be used as the primary or initial imaging modality when an

alternative lower dose imaging modality is adequate for the clinical purpose.

9.1.5

88 CBCT examinations shall not be used for routine or serial orthodontic

imaging.

9.1.5.9

89 Manufacturers should develop PKA values for CBCT acquisitions and provide

conversion coefficients or other dose metrics necessary for the calculation of

effective dose in order to allow an estimate of risk for each acquisition.

9.2.1

90 Only hand-held dental x-ray devices cleared by FDA for sale in the United

States shall be used.

10.1.3

91 Regulations preventing the user from holding the x-ray unit should not be

applied to equipment cleared by FDA that is designed to be hand-held.

10.1.3

92 States should develop and apply specific regulations for the dental uses of

CBCT.

10.1.4

93 Radiation safety training shall be provided to all dental staff and other

personnel, including secretaries, receptionists, and laboratory technologists.

This training shall be commensurate with the individual’s risk of exposure

from ionizing radiation.

10.2

94 Every person who operates dental x-ray imaging equipment or supervises the

use of such equipment shall have current training in the safe and efficacious

use of such equipment.

10.2

95 The dentist should regularly participate in continuing education in all aspects

of dental radiology, including radiation protection.

10.2

96 Opportunities should be provided for auxiliary personnel to obtain appropriate

continuing education credits.

10.2

97 The manufacturer shall provide training pertaining to the safe operation of the

hand-held unit.

10.2.2.2


26

98 The manufacturer of hand-held dental x-ray units shall provide information

suitable for the qualified expert regarding radiation leakage, backscatter

radiation, and the importance of the integral radiation shield.

10.2.3

99 The predoctoral dental curricula shall include didactic and clinical education

on physics of CBCT image production, artifacts that can lead to image

degradation, indications, and limitations of CBCT in dental practice, and the

effects of acquisition parameters on radiation dose.

10.2.3.1

100 Postdoctoral or clinical residency curricula shall expand upon the predoctoral

education and include discipline-specific indications and limitations of CBCT

imaging and the effects of acquisition parameters on radiation dose.

10.2.3.1

101 Dental practitioners who own CBCT units or use CBCT data sets in their

clinical practice and who have not received CBCT education as part of their

predoctoral or postdoctoral education shall acquire equivalent understanding

of the basic radiation safety aspects of CBCT imaging and sufficient

knowledge in the indications and limitations of CBCT imaging.

10.2.3.1

102 Dental personnel who operate CBCT units shall be adequately trained in the

proper operation and safety of the units. They should demonstrate adequate

knowledge of different protocols affecting the image quality and radiation

dose to the patient.

10.2.3.1

103 Prior to working with CBCT equipment, operators shall receive education on

the basics of CBCT technology, the risks associated with radiological imaging,

and training on the effective operation of CBCT equipment. This education

must include principles of CBCT image formation, equipment settings and

their impact on patient dose, and common artifacts associated with CBCT

images.

10.2.3.2


27

104 All operators shall complete training on each individual CBCT system they

will be using, as provided by the manufacturer. This device specific training

must include patient positioning, the range of user selectable exam settings,

and their effect on dose, protocol selection, image processing options, and

periodic maintenance schedules.

10.2.3.2

105 A qualified expert shall have appropriate training and mentored experience in

the evaluation of dental CBCT facilities prior to functioning independently.

10.2.3.3

106 Every person who operates CBCT equipment, supervises the use of CBCT

equipment or tests and evaluates the functions of CBCT equipment shall have

ongoing continuing education in the safe and effective use of that equipment.

10.2.3.4

415


28

2. Introduction 416

417

Radiology is an essential component of dental diagnosis. While available data clearly show 418

that ionizing radiation at modest to high doses produces biological damage, there is considerable 419

uncertainty and disagreement regarding the existence and nature of biological damage at very 420

low doses such as used in dental diagnosis except for some cone beam computed tomography 421

(CBCT) examinations. Given the billions of dental exposures annually across the population, it is 422

only prudent to address the controversy by assuming that there is a small but real risk of harm, 423

and to promulgate recommendations that foster safe and effective use of diagnostic dental 424

imaging to protect patients, staff and the public from radiogenic harm. Furthermore, the 425

practitioner may reasonably expect that the health benefit to the patient from dental radiographic 426

examination will outweigh any potential risk from radiation exposure provided that the: 427

428

dental radiographic examination is clinically indicated and justified; 429

radiographic technique is optimized to ensure images adequate for diagnosis at the lowest 430

dose consistent with this aim; and 431

principles outlined in this Report are followed to minimize exposure to the patient, staff, 432

and the public. 433

434

Office design, imaging and associated equipment, and procedures that minimize patient 435

exposure will also reduce exposure to the operator, other staff, and the public. Additional 436

measures, however, may be required to ensure that doses to operators and the public are within 437

limits established by regulatory bodies. Doses to all should be kept as low as reasonably 438

achievable (i.e., the ALARA principle) (NCRP, 1990). For operators and the public, the ALARA 439

principle encourages further reduction of doses that are already below regulatory limits. The 440

concept may be extended to patients, for whom dose limits do not apply. In this case, however, 441

we must assure that the imaging chain is optimized such that lower radiation doses are sufficient 442

to produce images of clinically acceptable quality. The process of balancing image quality with 443

radiation dose is known as optimization. 444

445


29

2.1 Purpose 446

447

The main objective of this Report is to present rationale, methods, and procedures for 448

radiation protection of patients, staff in the dental office and the public. The goals are: 449

450

1. eliminate unnecessary radiation exposure to the patient by assuring that images are 451

obtained only when justified and necessary; 452

2. assure that imaging equipment operates properly; 453

3. assure that images are of diagnostic quality; and 454

4. limit radiation exposure and meet the ALARA principle for staff and for patients. 455

456

This Report makes a number of recommendations to achieve these goals in the dental office. 457

458

2.2 Scope 459

460

This Report provides guidelines for radiation protection regarding the use of x rays in dental 461

practice. It replaces the National Council on Radiation Protection and Measurements Report 462

No. 35 (NCRP, 1970) and Report No. 145 (NCRP, 2003) in their entireties. It presents 463

recommendations regarding the optimization and clinically appropriate use of dental x-ray 464

equipment, as well as recommendations for radiation protection surveys, and monitoring of 465

personnel. Sections are included as specific guidance for dentists, their clinical associates, and 466

qualified experts conducting radiation protection surveys, equipment performance evaluations, 467

and determining facility shielding and layout designs; discussions of administrative and 468

educational considerations are also included. Additionally, there is guidance for equipment 469

designers, manufacturers, and service personnel. Basic guidance for dentists and their office staff 470

are contained in the body; technical details are provided in the appendices. 471

472

The target audience may not have easy access to related documents, therefore this Report is 473

intended to serve as a complete reference, providing sufficient background and guidance for 474

most dental imaging applications. Additional details regarding general medical and related topics 475


30

may be found in other reports of the NCRP (1976; 1988; 1989a; 1989b; 1990; 1992; 1993a; 476

1993b; 1997; 1998; 2000; 2001; 2004; 2005; 2008; 2009; 2012a; 2012b; 2013). 477

478

This report is to focuses particularly on those imaging procedures commonly performed in 479

dental facilities, including film, digital and hand-held intraoral radiography, and panoramic, 480

cephalometric, and cone beam computed tomography exams, and their associated equipment and 481

techniques. Except as otherwise specified, the recommendations in this Report apply to these 482

equipment and procedures. Other procedures of oral and maxillofacial radiology that are not 483

generally practiced in the dental office and that require more sophisticated equipment are subject 484

to the requirements and recommendations for medical radiology (NCRP, 1989a; 1989b; 2000; 485

2013), and will not be specifically addressed in this report. 486

487

2.3 Radiation Protection Philosophy 488

489

Biological effects of ionizing radiation fall into two classes. Tissue reactions (also known as 490

deterministic effects) and stochastic effects (Appendix I). Tissue reactions occur in all 491

individuals who receive a sufficiently high dose, i.e., exceeding some threshold. Examples of 492

these effects are acute radiation sickness, cataracts, skin burns, and epilation. Their severity 493

increases with increasing dose, and there is a threshold dose below which no clinically-494

significant tissue reactions occur. Stochastic effects, such as cancer, are all-or-nothing effects: 495

either a radiation-induced cancer occurs or it does not, and its severity is not dependent on 496

radiation dose. The probability of its occurrence increases with increasing dose, implying the 497

absence of a threshold. 498

499

The basic goal of radiation protection is to prevent in exposed individuals the occurrence of 500

tissue reactions and to reduce the risk for stochastic effects to an acceptable level when benefits 501

of that exposure are considered (NCRP, 1993a; 2004). 502

503

Achievement of this goal requires two interrelated activities: (1) efforts to ensure that no 504

occupationally exposed individual or member of the public receives doses greater than the limits 505

recommended for occupational and public exposures; and (2) efforts to ensure that patient doses 506


31

are ALARA . In most applications, ALARA is simply the extension into health care of good 507

radiation protection programs and practices that have traditionally been effective in keeping the 508

average of individual exposures of monitored workers well below the limits. Cost-benefit 509

analysis is applied to measures taken to achieve ALARA goals. For each source or type of 510

radiation exposure, it is determined whether the benefits outweigh the costs. Second, the relation 511

of cost to benefit from the reduction or elimination of that exposure is evaluated. Frequently 512

costs and benefits are stated in disparate units. Costs may be in units such as adverse biological 513

effects or economic expenditure. Benefits may be in units such as disease detected or lives saved. 514

Three principles provide the basis for all actions taken for purposes of radiation protection in 515

diagnostic imaging. These principles are applied differently for patients, occupationally exposed 516

persons, and the public. They are. 517

518

1. Justification: The benefit of radiation exposure outweighs its accompanying risks; 519

2. Optimization of protection: Total exposure remains as low as reasonably achievable 520

(ALARA); 521

3. Application of dose limits: For occupational and public exposure, dose limits are applied 522

to each individual to ensure that no one is exposed to an unacceptably high risk. 523

524

All three of these principles are applied to evaluation of occupational and public exposure. 525

Only the first two apply to exposure of patients. Dose limits do not apply to patients because 526

medical and dental exposures are obtained for diagnostic purposes that benefit the patient. The 527

primary objective of medical and dental imaging is to ensure that the health benefit exceeds the 528

risk to the patient from that exposure. 529

530

NCRP has established recommended dose limits for occupational and public (nonmedical) 531

exposure (Table 2.1) (NCRP, 2004b). Limits have been set below the estimated human threshold 532

doses for tissue reactions. NCRP assumes that for radiation protection purposes, the risk of 533

stochastic effects is proportional to dose without threshold, throughout the range of dose and 534

dose rates of importance in routine radiation protection (NCRP, 1993). This principle was used 535

to set dose limits for occupationally-exposed individuals such that estimated risks of stochastic 536


32

TABLE 2.1—Recommended dose limits (NCRP, 2004b).a 537

Basis Dose Limit

Occupational

Stochastic effects 50 mSv annual effective dose [10 mSv (x) ・ age (y) = cumulative

effective dose]

Deterministic effects

(tissue reactions)

150 mSv annual equivalent dose to the lens of the eye

500 mSv annual equivalent dose to skin, hands, and feet

Publicb

Stochastic effects 1 mSv annual effective dose for continuous or frequent exposure

5 mSv annual effective dose for infrequent exposure

Tissue reactions 15 mSv annual equivalent dose to the lens of the eye

50 mSv annual equivalent dose to the hands, skin, hands, and feet

Embryo and Fetus

0.5 mSv equivalent dose in a month from occupational exposure of

the mother once pregnancy is declared

aThe appropriate dose limits for adult students (i.e., age 18 y or older) in dental, dental 538

hygiene, and dental assisting educational programs depend on whether the educational entity 539

classifies the student as occupationally exposed or not. Additional guidance for radiation 540

protection practices for educational institutions is given in NCRP (2007). Dose limits for 541

students under 18 y of age correspond to the limits for members of the public (NCRP, 2004b). 542

bThese limits do not apply to exposures for medical or dental diagnosis or treatment. 543

544


33

effects are no greater than risks of occupational injury in other vocations that are generally 545

regarded as safe. 546

547

Dentists shall use x-ray equipment and procedures in a manner that ensures compliance with 548

both the recommendations in this Report and the requirements of their state or local jurisdictions. 549

When there is conflict between the recommendations in this Report and applicable legal 550

requirements, the more rigorous shall take precedence. 551

552


34

3. General Considerations 553

554

All persons are exposed to radiation in their daily lives (NCRP, 1987a; 1987b; 1987c; 555

1987d; 1989c; 1989d, 2009). NCRP has estimated the average total annual effective dose per 556

individual in the U.S. population in 2006 from all sources of radiation in the United States as 557

6.2 mSv (Figure 3.1). Approximately 3 mSv of this arises from naturally-occurring sources; 558

these sources have been present since the beginning of the Earth. Medical imaging contributes 559

48 % of the annual effective dose per individual. This represents an increase by a factor of 2.2 560

from the early 1980s to 2006, and is primarily due to increased utilization of the medical 561

modalities of computed tomography, nuclear medicine, and interventional fluoroscopy (NCRP, 562

2009) Dental radiation is a minor contributor to total population burden. However, the increasing 563

use of cone beam CT imaging, increases in conventional dental imaging, and revisions in the 564

ICRP Tissue Weighting Factors (ICRP, 2007) results in a growing contribution of dental imaging 565

to the population effective dose. Thus, appropriate measures are necessary to maintain dental 566

radiation exposures ALARA. 567

568

3.1 Dose Limits 569

570

The Council has recommended annual and cumulative dose limits for individuals from 571

occupational radiation exposure, and separate annual dose limits for members of the public from 572

sources of man-made radiation (Table 2.1) (NCRP, 1993a). The dose limits do not apply to 573

diagnostic or therapeutic exposure of the patient in the healing arts. (Some states may have 574

adopted different occupational limits.) 575

576

The cumulative limit for occupational dose is more restrictive than the annual limit. For 577

example, an individual who begins at 18 y of age to receive annual occupational effective doses 578

of 50 mSv will in 4 y receive 200 mSv, approaching the cumulative limit of 220 mSv at 22 y of 579

age. At that point, occupational exposure to that individual would be constrained by the 580

cumulative, not the annual limit. That is, the individual would then be limited to a cumulative 581

effective dose at the average rate of 10 mSv y-1, with a maximum rate of 50 mSv in any 1 y. The 582


35

583

584

585

586

587

588

589

590

591

592

593

594

595

596

597

598

599

Fig. 3.1. Percent contribution of various sources of exposure to the total collective effective 600

dose (1,870,000 person-Sv) and the total effective dose per individual in the U.S. population 601

(6.2 mSv) for 2006. Percent values have been rounded to the nearest 1 %, except for those <1 % 602

(NCRP, 2009). Conventional dental imaging accounts for 0.25 % of the dose from all medical 603

imaging (White and Pharoah, 2014); however, the contribution of cone beam CT imaging to the 604

computed tomography dose (medical) is at present unknown, and likely increasing. 605

606


36

duties of any individual who approaches the annual or cumulative limit may be changed so the 607

limit is not exceeded. It should be stressed that these are occupational exposures and not 608

exposures from medical diagnosis or treatment. 609

610

Average dental occupational exposures are usually only a small fraction of the limit and are 611

less than most other workers in the healing arts (Table 3.1) (Kumazawa et al., 1984). 612

Occupational exposures have been declining (Figure 3.2) over recent decades in workers in both 613

the healing arts in general and dentistry in particular (HSE, 1998; Kumazawa et al., 1984; 614

UNSCEAR, 2000). It seems reasonable to conclude that no dental personnel will receive 615

occupational exposures exceeding the limit as long as proper facility design, equipment 616

performance, and operating procedures are implemented. 617

618

Facilities are designed, operated, and monitored such that no individual member of the public 619

receives a dose in excess of the recommended limit. Therefore, members of the public are not 620

monitored. 621

622

While there are no recommended dose limits for medically necessary radiation exposure, the 623

ALARA principle of radiation protection optimization can be applied to patients as well. For 624

dental exposures of patients, The NCRP agrees with the statement by ICRP (2007b, paragraph 625

70): “The optimization of radiological protection means keeping the doses ‘as low as reasonably 626

achievable, economic and societal factors being taken into account, and is best described as 627

management of the radiation dose to the patient to be commensurate with the [dental] purpose.” 628

That ICRP publication clarifies the goal of the ALARA principal in medical [dental] imaging 629

(paragraph 47): “In medicine [dentistry] the requirement is to manage the radiation dose to the 630

patient to be commensurate with the medical [dental] purpose. The goal is to use the appropriate 631

dose to obtain the desired image or desired therapy.” 632

633

Facility design, x-ray equipment performance, and operating procedures shall be established 634

to maintain patient, occupational and public exposures as low as reasonably achievable 635

(ALARA). When new equipment is installed or substantially different practices are 636

637


37

TABLE 3.1—Occupational doses in the healing arts, United States, 1980.a 638

Occupation

Number of Workers Mean Annual Whole-Body Dose

(mSv)

Totalb Exposedc Totalb Exposedc

Hospital 126,000 86,000 1.4 2.0

Medical offices 155,000 87,000 1.0 1.8

Dental (offices) 259,000 82,000 0.2 0.7

Podiatry 8,000 3,000 0.1 0.3

Chiropractic 15,000 6,000 0.3 0.8

Veterinary 21,000 12,000 0.6 1.1

Total 584,000 276,000 0.2 1.5

aKumazawa et al. (1984). 639

bAll workers with potential occupational exposure. 640

cWorkers who received a measurable dose in any monitoring period during the year. 641

642


38

643

644

645

646

647

648

649

650

651

652

653

654

655

Fig. 3.2. Decline in mean occupational doses over recent decades, for workers in all healing 656

arts combined and dentistry. U.S. data at 5 y intervals from 1960 to 1980 plus that projected for 657

1985 were reported as dosimeter readings (Kumazawa et al., 1984). World estimates from 1975 658

to 1995 were reported as effective doses and are plotted at each 5 y interval (UNSCEAR, 2000). 659

660


39

implemented, staff shall wear personal radiation badges for 1 y to ascertain the level of typical 661

radiation doses (Section 4.5.5). 662

663

All individuals engaged in dentomaxillofacial imaging shall meet the following radiation 664

protection limits: 665

666

Recommendation 1. No individual worker shall receive an occupational effective dose in 667

excess of 50 mSv in any 1 y. 668

669

Recommendation 2. The numerical value of the individual worker’s life-time 670

occupational effective dose shall be limited to 10 mSv times the value of his or her age in 671

years. Occupational equivalent doses shall not exceed 0.5 mSv in a month to the embryo 672

or fetus for pregnant individuals, once pregnancy is known. 673

674

Recommendation 3. Mean nonoccupational effective dose to frequently or continuously 675

exposed members of the public shall not exceed 1 mSv y-1 excluding doses from natural 676

background and medical care); infrequently exposed members of the public shall not be 677

exposed to effective doses >5 mSv in any year. 678

679

NOTE: NCRP is presently engaged in a major review of NCRP Report No. 116, Radiation 680

Protection Guidance for the United States. NCRP may issue a new report with different 681

occupational and public dose limits that would supersede those specified in Recommendations 1 682

to 3 above. Ultimately, practitioners must comply with applicable federal and state regulations 683

regarding exposure of workers and the public. 684

685

3.2 Role of Dental Personnel in Radiation Protection 686

687

ALARA requires optimizing the practices of all dental personnel who are involved in 688

prescription, exposure, processing, evaluation, and interpretation of dental images. This Section 689

describes the roles of each. 690

691


40

3.2.1 The Dentist 692

693

In most dental facilities a single dental practitioner is responsible for the design and conduct 694

of the radiation protection program . In large facilities, such as dental educational institutions, the 695

authority and responsibility for design and oversight of the radiation protection program may be 696

delegated to a specific employee with special expertise in the field. This individual is designated 697

the radiation safety officer. The dentist in charge, in consultation with the radiation safety officer 698

(if that person is someone other than the dentist) and with a qualified expert, is responsible for 699

implementing the radiation protection program, which includes (NCRP, 1990; 1998). 700

701

establishing, reviewing, and documenting radiation protection procedures; 702

instructing all dental staff in radiation protection; 703

implementing radiation surveys and recording results and corrective actions; 704

establishing the monitoring of personnel, if required; 705

ensuring that all radiation protection features are functional and the required warning 706

signs are posted; 707

implementing and monitoring the ALARA principle; and 708

implementing and documenting quality assurance (QA) and quality control (QC) 709

procedures. 710

711

Guidance on developing appropriate radiation protection programs for a dental office can be 712

found in most contemporary oral radiology textbooks (White and Pharoah, 2014). 713

714

Recommendation 4. The dentist (or, in some facilities, the designated radiation safety 715

officer) shall establish and periodically review a radiation protection program. The 716

dentist shall seek guidance of a qualified expert in this activity. 717

718

The dentist is qualified by education and licensure to prescribe and perform radiographic 719

examinations and to evaluate and interpret the images produced. 720

721


41

Recommendation 5. The dentist shall employ published, evidence-based selection 722

criteria when prescribing radiographs. 723

724

Additional details concerning selection criteria are found in Sections 4.4.1 and 9.1.5. 725

726

3.2.2 Auxiliary Personnel 727

728

In most dental facilities the staff involved in radiologic procedures consists of registered 729

dental hygienists and dental assistants who may or may not be certified. Registered hygienists 730

and certified assistants are trained and credentialed to perform radiological examinations, process 731

film, and digital images and evaluate them for quality (NRPB, 2001). In some states noncertified 732

assistants may be credentialed for these procedures upon completion of approved training. 733

734

Recommendation 6. Radiological procedures shall be performed only by dentists or by 735

legally qualified and credentialed auxiliary personnel. 736

737

3.2.3 The Qualified Expert 738

739

This individual is qualified by education and experience to perform advanced or complex 740

procedures in radiation protection that generally are beyond the capabilities of most dental 741

personnel (NRPB, 2001). These procedures include facility design to provide adequate shielding 742

for protection of the occupationally exposed and the public, inspection and evaluation of 743

performance of x-ray equipment, evaluation of and recommendations for radiation protection 744

programs, and to assist in optimizing image quality and patient radiation dose. Usually 745

possessing an advanced degree in medical physics or a similar field, this individual is usually 746

certified by the American Board of Radiology, the American Board of Medical Physics, or 747

equivalent. Care must be taken to ensure that the qualified expert’s credentials include 748

knowledge and familiarity with dental radiologic practices. Some otherwise highly qualified 749

experts may have little experience in dental radiological practices. (Some states credential or 750

license these individuals.) The principal responsibility of this person is to serve as a consultant to 751

the dentist. 752


42

753

The qualified expert adds essential value to the dental practice by providing expertise in 754

radiation shielding design, radiation safety for the staff and general public, applicable regulatory 755

and accreditation requirements, and establishing the quality control program. Specifically, the 756

qualified expert: 757

758

Performs a pre-installation radiation shielding design and plan review. 759

Performs acceptance testing [equipment performance evaluation (EPE)] and a post-760

installation radiation protection survey. 761

Initiates the quality control program by evaluating the initial characteristics of the x-ray 762

beam, measuring patient exposures, and assessing image quality. 763

Establishes the quality control program by advising on the individual elements of the QC 764

program, procedures to be followed, the qualifications of personnel, expected ranges of 765

results, and actions to be taken when results are beyond the expected ranges. Quality 766

control programs for dental offices are described in oral and maxillofacial radiology 767

textbooks (White and Pharoah, 2014). 768

Compares measured metrics of dose to the patients with published Diagnostic Reference 769

Levels and Achievable Doses. 770

Advises on the x-ray exposure parameters (e.g., exposure time, tube potential, field size 771

or collimation, and other technique factors) to be used to achieve optimum image quality 772

and minimal radiation dose (optimization). 773

774

Recommendation 7. The qualified expert should provide guidance for the dentist or 775

facility designer in the layout and shielding design of new or renovated dental facilities 776

and when equipment is installed that will significantly increase the air kerma incident 777

on walls, floors, and ceilings. 778

779

Recommendation 8. The qualified expert shall provide guidance for the dentist 780

regarding establishment of radiation protection policies and procedures. 781

782


43

3.3 Electronic Image Data Management 783

784

Secure management of patient image data is an important aspect of quality assurance and 785

overall proper care of patients. Thus, image data must be stored in a way that provides robust 786

security, allows routine access for the practitioner or designee, and enables secure transmission 787

of the image data to other practitioners for consultation or at the request of the patient. 788

789

The electronic health record in a dental office should allow for interaction with a properly 790

configured picture archiving and communication systems (PACS) or should have as a subset a 791

good PACS within its architecture. The PACS is a major component in radiology in dentistry and 792

medicine and is the backbone of digital imaging. It is recommended that images that are stored in 793

the PACS system be in the Digital Imaging and Communications in Medicine (DICOM) 794

standard format. DICOM is the standard for the communication and management of medical 795

imaging information and related data. If a practitioner is using a proprietary storage and 796

communication system that comes with their x-ray equipment, this system should fulfill the basic 797

functions of a PACS system and should store it’s electronic image data in the DICOM format. 798

799

The ability of PACS systems to share imaging data can benefit patients by reducing the 800

likelihood that an x-ray exam is needlessly repeated.. A lack of data sharing in dental imaging is 801

a major problem and often responsible for repeated x-ray exposures because many data systems 802

presently in use do not integrate well with other systems or products, often requiring repeated 803

exposures. 804

805

The benefits of a good PACS system include: 806

807

1. secure storage of images; 808

2. organization of images; 809

3. archiving of current and older images; 810

4. easy workflow organization; 811

5. distribution of images and associated metadata (e.g., image interpretation, photos, 812

histopathologic findings); 813


44

6. restoration of lost d to prevent downtime and prevent the need to retake images; and 814

7. possible web access to images and data. 815

816

The PACS should allow for: 817

818

1. high quality display of images; 819

2. appropriate adjustment of images (post processing, i.e., window and level adjustment); 820

3. support for multimodality images; 821

4. customizable protocols and display of technical factors; 822

5. the use of templates to create structured reports which include estimated radiation dose to 823

the patient; 824

6. built in quality assurance tools; 825

7. automatic backups; 826

8. retrieval of accessed data; 827

9. easy upgrading; 828

10. compatible with open standards; 829

11. easy integration with electronic health records; and 830

12. easy integration of third party voice transcription software. 831

832

Data management in dentistry and medicine falls under the purview of the Health 833

Insurance Portability and Accountability Act of 1996 (HIPAA), with the primary goal of 834

protecting the confidentiality and security of the electronic health care information of patients. 835

Failure to comply with HIPAA may result in civil and criminal penalties. 836

837

Recommendation 9. To avoid unnecessary repeat exposures due to lost images or 838

redundant examinations, the electronic image data management system shall provide 839

for secure storage, retrieval, and transmission of image data sets 840

841

Recommendation 10. All digital images acquired shall be retained in the patient’s 842

electronic record. 843

844

Recommendation 11. All digital images should be backed up offsite electronically in a 845

separate, safe, and secure location at regular intervals. 846


45

4. Radiation Protection in Dental Facilities 847

848

Radiation protection recommendations specific to the dental facility are provided in this 849

Section. Technical details are found in the appendices. 850

851

4.1 General Considerations 852

853

Facilities are occupied by patients, dentists, clinical and nonclinical staff, and the public. 854

Therefore, facilities must be designed with the radiation protection and safety of all of these 855

groups. 856

857

From a radiation protection perspective, dental x-ray equipment (both permanently mounted 858

and hand-held equipment) must be installed and utilized so that patient and personnel exposures 859

are maintained ALARA, while simultaneously providing the image quality necessary to meet the 860

clinical needs. An experienced x-ray equipment provider may suggest possible configurations to 861

meet the needs and limitations of each practice environment. However, the qualified expert 862

should review the anticipated workload and proposed installation plan before renovation, 863

construction, and installation begins, to assure that each individual room configuration will meet 864

local regulatory requirements and the ALARA principle. The shielding principles used may be 865

found in NCRP Report No. 147 (NCRP, 2004a). 866

867

Perhaps the most important and often overlooked requirement of an equipment installation 868

plan is that, after positioning the patient and the imaging equipment, the operator must be able to 869

see and hear the patient while initiating the x-ray exposure. This is essential to assure that the 870

patient (or the x-ray equipment) has not moved since positioned by the operator. This may be 871

accomplished by the operator standing in a doorway (if the distance is adequate for radiation 872

protection), viewing the patient through a window designed to meet the radiation protection 873

goals, mirror or video monitoring system, or any other means that assures continuous visual and 874

audible communication between the patient and the operator. 875

876


46

Depending on the room size, workload, and x-ray modality used, for typical intraoral dental 877

radiography installations, it is common (but not always true) that commercial construction (two 878

layers of 5/8 inch gypsum wallboard, or GWB) provides sufficient radiation protection, since 879

GWB attenuates x-radiation in the dental diagnostic range. High workloads, small rooms and 880

proximity to other persons may increase the shielding requirements. The qualified expert should 881

perform a pre-installation shielding design and a post-installation shielding survey. 882

883

4.1.1 Shielding Design 884

885

Shielding design must be included in facility planning (before floor plans are completed) to 886

ensure that neither occupational nor public doses exceed established limits. The qualified expert 887

may present more than one shielding design for a facility. Each design may include office 888

layouts, equipment locations, doorway positions, construction of partitions, etc. Construction 889

costs vary directly with the magnitude of dose reduction. With innovative design, dose 890

reductions can be achieved at little or no cost and without adverse impact on patient care (i.e., the 891

ALARA principle). 892

893

Recommendation 12. The qualified expert should perform a pre-installation radiation 894

shielding design and plan review, to determine the proper location and composition of 895

barriers used to ensure radiation protection in new or renovated facilities, and when 896

equipment is installed that will significantly increase the air kerma incident on walls, 897

floors, and ceilings. 898

899

Recommendation 13. The qualified expert shall perform a post-installation radiation 900

protection survey to assure that radiation exposure levels in nearby public and 901

controlled areas are ALARA and below the limits established by the state or other local 902

agency with jurisdiction. 903

904

The essential radiation safety requirement of structural shielding is that the exposure to 905

persons near the x-ray equipment shall be maintained ALARA, and within specific requirements 906


47

set by the state or other jurisdiction. The following general considerations apply to most dental 907

imaging facilities: 908

909

1. Due to the relatively low levels of scattered radiation produced during most intraoral, 910

cephalometric, and panoramic x-ray installations, it is common (though not always true) 911

that the shielding provided by drywall (GWB) used in routine construction will provide 912

sufficient radiation shielding without the need for additional lead or other special 913

shielding materials. The location of walls and doors are an essential component of the 914

room shielding configuration. 915

2. In the design of x-ray shielding, dentists, dental hygienists, and dental assistants are 916

considered to be occupationally exposed personnel. All other persons should be 917

considered members of the general public. 918

3. To minimize unnecessary radiation exposure due to repeated exams, the operator shall 919

maintain visual and audible contact with the patient, or with the care provider of a 920

nonverbal patient, during each x-ray exposure. The qualified expert should keep this in 921

mind and specify the recommended location of the operator during each exposure. 922

4. While it is common to install CBCT systems to replace previously existing panoramic 923

dental radiographic systems, CBCT systems produce substantially more scattered 924

radiation than panoramic dental units (typically by at least a factor of 10). Hence, 925

shielding or location of panoramic rooms will often be insufficient for a CBCT system. 926

5. Some dental facilities equip and utilize a special “x-ray room” for multiple x-ray imaging 927

examinations: intraoral, cephalometric, panoramic, or CBCT imaging. Cumulative 928

radiation exposures resulting from representative weekly workloads in each modality 929

must be considered when designing shielding for such a room. 930

931

Detailed discussions of all aspects of shielding design for dental facilities, including CBCT 932

facilities, are found in Appendix D. 933

934

Recommendation 14. The qualified expert should assess each facility individually and 935

document the recommended shielding design in a written report. 936


48

937

Recommendation 15. The qualified expert should consider the cumulative radiation 938

exposures resulting from representative workloads in each modality when designing 939

radiation shielding for rooms in which there are multiple x-ray machines. 940

941

Some facilities include rooms with multiple x-ray machines. Shielding design for such rooms 942

assumes that only one patient is imaged at any one time. 943

944

Recommendation 16. The facility shall establish administrative controls that assure no 945

more than one patient is in an x-ray room with multiple x-ray machines during any x-946

ray exposure. 947

948

4.1.2 Equipment Performance Evaluations and Radiation Protection Surveys 949

950

Initial and periodic equipment performance evaluations (EPE) are the responsibility of the 951

qualified expert. This testing is performed to determine compliance with laws and regulations 952

governing the safety and performance of the equipment, assure that patient doses and image 953

quality are optimized, and verify the validity of the technique charts. In addition, this evaluation 954

includes assuring that the equipment is being used in a manner compatible with standards of 955

good radiologic practice. 956

957

Newly installed equipment also must comply with all applicable federal performance 958

standards (FDA, 2015). While this compliance is certified by the equipment installer, the initial 959

performance of new equipment is determined by the qualified expert through acceptance testing. 960

Acceptance testing ensures that the new equipment performs as specified in the agreement 961

between the buyer and seller, and may address equipment performance beyond the scope of the 962

federal performance standard. Any deviations are reported to the dentist, who is responsible for 963

corrective action. 964

965

Recommendation 17. A qualified expert shall evaluate x-ray equipment to ensure that it 966

is in compliance with applicable governing laws and regulations. 967


49

968

Dental x-ray facilities must have a radiation protection survey before the imaging equipment 969

is used to assure that the radiation protection is sufficient to meet the design goals and regulatory 970

limits. In addition, a survey shall be made after any change in the installation, workload, or 971

operating conditions that might significantly increase occupational, patient, or public exposure 972

(including x-ray machine service or repair that could affect the x-ray machine output or 973

performance). 974

975

These surveys and EPEs are performed by a qualified expert and should be performed at 976

regular intervals. This interval should not exceed 4 y for intraoral, panoramic or cephalometric 977

equipment, and should not to exceed 2 y for CBCT units. 978

979

The essential elements of a survey and EPE performed by a qualified expert should include: 980

981

1. radiation safety survey; 982

2. occupational radiation exposure assessment; 983

3. evaluation of image receptor performance and dose; 984

4. evaluation of the x-ray generator and radiation output characteristics; 985

5. evaluation of beam collimation and filtration; and 986

6. clinical image quality. 987

988

Detailed descriptions of these survey elements and a sample CBCT radiation protection 989

survey can be found in Appendices D and H. 990

991

Recommendation 18. All new dental x-ray installations shall have a radiation protection 992

survey and equipment performance evaluation carried out by, or under the direction of, 993

a qualified expert. 994

995

Constancy testing is a periodic equipment performance evaluation carried out by a qualified 996

expert to determine whether x-ray producing and imaging systems continue to meet performance 997


50

standards established during acceptance testing. If acceptance testing data is unavailable, the 998

qualified expert uses manufacturer’s specifications as performance criteria. 999

1000

Image quality and dose in dental radiography can be assessed by the use of devices that are 1001

mailed to dental intraoral facilities, exposed, and returned to the vendor for evaluation. These 1002

may be of particular utility for monitoring dental facilities in remote locations and facilities that 1003

are visited by a QMP less often than annually and for regulatory oversight. 1004

1005

Recommendation 19. Equipment performance evaluations shall be performed by a 1006

qualified expert at regular intervals thereafter, preferably at intervals not to exceed 4 y 1007

for facilities only with intraoral, panoramic or cephalometric units. Facilities with 1008

CBCT units shall be evaluated every 1 to 2 y. 1009

1010

4.1.3 Signage 1011

1012

Some states require clearly visible signage in the patient care areas. This may include posted 1013

statements identifying radiation use areas or in imaging rooms instructing patients to notify 1014

dentist and staff if they are or may be pregnant. 1015

1016

4.2 Diagnostic Reference Levels and Achievable Doses 1017

1018

Diagnostic reference levels (DRLs) and achievable doses (AD) can be used as guidance in 1019

optimizing the doses to patients from dental imaging examinations. In particular, DRLs can be 1020

used to help ensure that patient radiation doses are not grossly excessive. 1021

1022

NCRP Report No. 172 (NCRP, 2012) describes DRLs and ADs and their uses, describes the 1023

history of their development, and provides suggested values for the United States for a variety of 1024

imaging modalities and procedures. In particular, it defines a DRL as: 1025

1026

“A radiation dose level serving as an investigational level. When doses exceed the DRL the 1027

reasons for the higher doses should be investigated. A process known as optimization is used 1028


51

to assure that the image quality is adequate for the clinical task and that the patient doses are 1029

appropriate.” The diagnostic reference level is typically set at the 75th percentile of the 1030

distribution of dose metrics from a representative sample of facilities. 1031

1032

And an achievable dose as: 1033

1034

“A dose which serves as a goal for optimization efforts. This dose is achievable by standard 1035

techniques and technologies in widespread use, while maintaining clinical image quality 1036

adequate for the diagnostic purpose. The achievable dose is typically set at the median value 1037

of the dose distribution.” 1038

1039

Dose metrics used to generate DRLs and ADs may be based upon dose measurements made 1040

by qualified experts or others during simulated examinations without the presence of a patient or 1041

from dose metrics recorded by the x-ray imaging systems from actual patient examinations. To 1042

date, DRLs provided by the NCRP for use in the United States have been based, primarily, upon 1043

data collected by the former method (NCRP, 2012b). There are advantages and disadvantages to 1044

both methods. For patient examination-based DRLs, inaccuracy in the calibration of the dose 1045

measurement system of the imaging device is a potential source of error. Another source of 1046

variability in patient measurements is the variability in the size of the patient. Radiation 1047

exposures can vary substantially for the same examination depending on the thickness of the 1048

patient for the same body part. Alternatively, it takes considerably more effort to measure doses 1049

than to simply record dose metrics from patient examinations. 1050

1051

There are few sources of data today in the United States for use in determining DRLs and 1052

ADs. The U.S. Food and Drug Administration’s (FDA) Center for Devices and Radiological 1053

Health (CDRH), the Conference of Radiation Control Program Directors (CRCPD), and many 1054

states in the United States collaborate in the Nationwide Evaluation of X-ray Trends (NEXT) 1055

program. Data on the radiation exposures for selected diagnostic x-ray exams are collected from 1056

nationally representative samples of clinical facilities in the United States. The initial such 1057

NEXT survey of dental imaging was conducted in 1999; its findings were initially reported in 1058


52

2007 (Moyal, 2007). At the time of writing, another NEXT survey of dental imaging was 1059

recently completed (Farris and Spelic, 2015). 1060

1061

Another potential source of data for DRLs and ADs is a registry that would automatically 1062

collect dose metrics from dental examinations. The American College of Radiology maintains a 1063

dose registry for diagnostic CT and other examinations. It would be extremely useful to have the 1064

ability to generate DRLs and ADs for CBCT examination in dentistry from a dental dose 1065

registry. 1066

1067

There are disadvantages to this process for creating and using DRLs and ADs in the United 1068

States. In particular, the NEXT process takes time and considerable effort to collect and analyze 1069

the dose data from a large number of institutions. This can limit the number of examinations for 1070

which DRLs and ADs are available and can also cause the DRLs and ADs to be based on data 1071

from many years ago, which may not be fully relevant to current usage and technology. 1072

1073

For examinations for which appropriate and recent DRLs for the United States are not 1074

available, an option is to use DRLs from other countries (e.g., Hart et al., 2012; Holroyd, 2011; 1075

2013). Another option is to compare the doses from a facility’s protocols with dose data 1076

collected by other reputable institutions. In either case, bias can be introduced due to differences 1077

in practice. 1078

1079

Each dental facility should compare its dose metrics against DRLs and ADs. When qualified 1080

experts or state inspectors test dental imaging systems, they should collect dose data in a manner 1081

suitable for comparison with DRLs and ADs. For imaging systems that display dose data, these 1082

data should be compared with DRLs and ADs. 1083

1084

Careful consideration should be given when there are different technologies in use for 1085

imaging. For example, currently, intra-oral radiography is being performed with film, 1086

photostimulable storage phosphor (PSP) plates, and direct digital radiography image receptors. 1087

The currently available DRLs and ADs are largely due to data from facilities using film. 1088

Facilities with direct digital receptors may presume that their doses are optimized if they are less 1089


53

than these DRLs and similar to the ADs, but in fact their doses may be higher than needed for 1090

clinically-adequate images. 1091

1092

The creation of interim DRLs and ADs, published in the literature from studies involving 1093

small numbers of reputable institutions, is recommended. 1094

1095

Recommendation 20 Diagnostic Reference Levels and Achievable Doses should be 1096

developed for dental CBCT imaging. 1097

1098

Recommendation 21. Each dental facility should record and track indicators of patient 1099

dose, such as entrance air kerma and associated technique factors. 1100

1101

Recommendation 22. Each dental facility should compare its doses to DRLs and ADs. 1102

In particular, where established methods exist, the qualified expert shall collect dose 1103

data suitable for comparison with DRLs and ADs. These data and the results shall be 1104

provided in the qualified experts report. For dental imaging systems that provide dose 1105

metrics for patient examinations, the dentist or qualified expert should periodically 1106

compare medians of these data for 10 clinical examinations appropriate for this purpose 1107

with DRLs and ADs. 1108

1109

Recommendation 23. Organizations such as NCRP, U.S. Food and Drug 1110

Administration (FDA), Conference of Radiation Control Program Directors (CRCPD), 1111

American Academy of Oral and Maxillofacial Radiology (AAOMR), and American 1112

Dental Association (ADA) should strive to provide DRLs and ADs for a variety of 1113

dental examinations. 1114

1115

4.3 Optimization of Image Quality and Patient Dose: General Principles 1116

1117

Clinical image quality and radiation dose to both patients and staff are the two primary 1118

concerns in dental x-ray imaging. The image produced must have sufficient detail and 1119

information to assure the practitioner that subtle pathology can be detected. Optimization is the 1120


54

balancing of image quality and patient dose. The optimization process is best carried out as a 1121

cooperative effort between dentists and qualified experts. 1122

1123

DRLs and ADs are helpful as part of the optimization process. However, a dose metric found 1124

to be less that the appropriate DRL and near the AD does not necessarily mean that the doses are 1125

optimized and that image quality is acceptable; in some cases a newer technology (e.g., digital 1126

intraoral image receptors) may produce acceptable diagnostic images at doses much lower than 1127

the older technology and, if the DRLs and ADs are largely based upon data from the less dose 1128

efficient technology, an optimized dose may be considerably less that the AD. Furthermore, 1129

optimization can be performed in the absence of DRLs and ADs. 1130

1131

For film radiography the optimization process starts with using EF-speed film, filling the 1132

processor with new developer and fixer, and assuring that the developer is at the temperature 1133

specified by the film manufacturer. The film processor should be performing with a consistent 1134

level of quality. Once the tube current (mA) and potential (kVp) are determined (either selected 1135

by the operator or fixed by the manufacturer), the next step is to optimize the exposure time. 1136

Begin with the film manufacturer’s recommendation for the average adult patient. On subsequent 1137

patients, reduce the exposure time until there is degradation of the image that renders it 1138

nondiagnostic; the baseline exposure time for the average adult patient is then set as one time 1139

station greater than the setting that produced the degraded, nondiagnostic image. As described in 1140

Section 5.1.3, this exposure setting should be incorporated into a technique chart. The chart 1141

should also include adjustments from this baseline exposure for children and for large and small 1142

adults and adolescents. 1143

1144

Having established clinically useful exposure settings, one should expose a stepwedge 1145

phantom with these settings in order to have a phantom-based image for subsequent quality 1146

control checks of film processing and darkroom integrity. 1147

1148

The steps for digital imaging systems are essentially the same as with film, but without the 1149

activities associated with the film processor. A phantom appropriate for the type of digital 1150


55

imaging should be used to establish the baseline image. CBCT units have special phantoms 1151

which are supplied by the manufacturer (Section 5.2.5). 1152

1153

The primary goal of optimization is to select x-ray techniques, and, consequently, patient 1154

doses, that produce clinically acceptable images at the lowest dose achievable (ALARA) 1155

regardless of whether the image receptor is film or digital. 1156

1157

4.4 Protection of the Patient 1158

1159

Potential health benefits to patients from dental x-ray exposure preclude establishment of 1160

dose limits for patients. Thus the specific goal of optimization of protection of the patient should 1161

be to obtain the necessary clinical information while avoiding unnecessary patient exposure, i.e., 1162

the patient exposure is maintained as low as reasonably achievable (ALARA). 1163

1164

4.4.1 Selection Criteria. Examination Type and Frequency 1165

1166

Elimination of unnecessary radiographic examinations is a very effective method for 1167

avoiding unnecessary patient exposure. Guidance on x-ray imaging appropriateness and selection 1168

criteria have been developed (FDA/ADA, 2015a; 2015b). Procedures are outlined in Sections 1169

4.4.1.1 through 4.4.1.3 for eliminating unnecessary examinations for both symptomatic patients 1170

seeking urgent care and asymptomatic patients scheduled for routine or continuing dental care. 1171

1172

A clear procedure for reducing the extent and frequency of dental radiographic examinations 1173

must be followed when a patient transfers or is referred from one dentist to another. Modern 1174

digital imaging and electronic transfer facilitates exchange of information among dentists and 1175

other health care providers. 1176

1177

Recommendation 24. All radiological examinations shall be performed only on direct 1178

prescription of the dentist, physician, or other individuals authorized by law or 1179

regulation. 1180

1181


56

Recommendation 25. Radiographic examinations shall be performed only when patient 1182

history and physical examination, prior images, or laboratory findings indicate a 1183

reasonable expectation of a health benefit to the patient. 1184

1185

Recommendation 26. For each new or referred patient, the dentist shall make a good 1186

faith attempt to obtain previous, pertinent images prior to acquiring new patient 1187

images. 1188

1189

4.4.1.1 Symptomatic Patients. When symptomatic patients are seen, the dentist is obligated to 1190

provide care to relieve those symptoms and, when possible, eliminate their cause. Radiographs 1191

required for that treatment are fully justified, but additional, noncontributory radiographs are not 1192

justified. For example, a full-mouth intraoral study is not warranted for emergency treatment of a 1193

single painful tooth. However, if treatment of that painful tooth is the first step in comprehensive 1194

dental care, then those radiographs required for that comprehensive care are justified. 1195

1196

Recommendation 27. For symptomatic patients, the radiological examinations shall be 1197

limited to those images required for diagnosis and treatment of current disease. 1198

1199

4.4.1.2 Asymptomatic Patients. Maintenance of oral health in asymptomatic new patients or 1200

those returning for periodic reexamination without clear signs and symptoms of oral disease may 1201

require radiographs. Selection criteria that will aid the dentist in selecting and prescribing 1202

radiographic examination of these patients have been published (FDA/ADA, 2015a; 2015b). 1203

These criteria recommend that dental radiographs be prescribed only when the patient’s history 1204

and physical findings suggest a reasonable expectation that radiographic examination will 1205

produce clinically useful information. 1206

1207

Recommendation 28. For asymptomatic patients, the extent of radiological examination 1208

of new patients, and the frequency and extent for established patients, shall adhere to 1209

current published, evidence based selection criteria. 1210

1211


57

4.4.1.3 Administrative Radiographs. Radiographs are occasionally requested, usually by outside 1212

agencies, for purposes other than health. Examples include requests from third-party payment 1213

agencies for proof of treatment or from regulatory boards to determine competence of the 1214

practitioner. In some institutions dental or dental auxiliary students have been required to 1215

perform oral radiographic examinations on other students for the sole purpose of learning the 1216

technique. Other methods (such as photographs for treatment documentation or image receptor 1217

and tube-head placement for radiologic technique training) that do not require exposure to x rays 1218

are generally available for providing this information. Dental students can learn to perform x-ray 1219

exams using phantoms. 1220

1221

Recommendation 29. Administrative use of radiation to provide information that is not 1222

necessary for the treatment or diagnosis of the patient shall not be permitted. 1223

1224

Recommendation 30. Students shall not be compelled or permitted to perform 1225

radiographic exposures of humans solely for purposes of education. 1226

1227

Recommendation 31. Candidates shall not be compelled or permitted to perform 1228

radiographic exposures of humans solely for purposes of licensure, credentialing or 1229

other certification. 1230

1231

4.4.2 X-Ray Machines 1232

1233

All x-ray machines should meet the design specifications and all requirements of the 1234

jurisdiction in which they are located. Equipment certified to conform to the federal performance 1235

standard (FDA, 2005) will generally meet these requirements. Equipment of recent manufacture 1236

(especially that manufactured in Europe) may also conform to IEC standards (IEC, 2012) or 1237

regulatory guidance (NRPB, 2001). Specific design considerations are covered in subsequent 1238

chapters that address specific imaging modalities. 1239

1240

Recommendation 32. Personnel responsible for purchase and operation of dental x-ray 1241

equipment shall ensure that such equipment meets or exceeds all applicable U.S. federal 1242


58

government and state requirements and regulations. In addition, the equipment should 1243

conform to current international standards for basic safety and essential performance. 1244

1245

4.4.3 Examinations and Procedures 1246

1247

The general requirements and recommendations in this Report apply to all dental radiological 1248

examinations and procedures. This Section, however, presents additional recommendations 1249

specific for particular radiographic examinations. 1250

1251

4.4.3.1 Intraoral Radiography. Dental intraoral radiographs and chest radiographs have been the 1252

most common diagnostic x-ray procedures in the United States. A 2005 to 2006 ADA survey 1253

(ADA, 2007), based on practitioner logs, found 308,061,820 periapical images and 423,995,407 1254

bitewing images produced annually in private practices, excluding the military, federal agencies, 1255

hospitals, and academic institutions. It is estimated that 493 million intraoral examinations were 1256

performed in the United States in 2014 (NEXT 2015). In both cases patient dose per image and 1257

resulting radiation detriment are low when compared to other x-ray imaging modalities such as 1258

computed tomography. However, the large number of intraoral x-ray procedures performed 1259

annually delivers a notable collective dose to the exposed population. Consequently, this requires 1260

diligence in optimizing the radiation exposure from these procedures so that unnecessary 1261

exposure is avoided and ensuring that such exams are performed only when there is an 1262

anticipated benefit to the patient. 1263

1264

4.4.3.2 Panoramic Radiography. Panoramic images provide curved-plane tomograms of the 1265

teeth and jaws. This imaging method is widely used in dental practice. A 2005 to 2006 ADA 1266

survey (ADA, 2007), based on practitioner logs, found 29,552,920 panoramic images produced 1267

annually in private practices, excluding the military, federal agencies, hospitals, and academic 1268

institutions. The major advantages are rapid acquisition of a single image encompassing the 1269

entire dental arches and their supporting structures. The zone of sharp focus (“focal trough”) is 1270

limited and varies with manufacturer and model. It is designed to accommodate average adults; a 1271

few machines allow adjustment to patient dimensions. Patient positioning is critical and varies 1272

with manufacturer and model. Some machines allow only limited adjustment of beam technical 1273


59

factors such as image receptor speed, patient thickness and tube current. Effective dose to the 1274

patient for a single panoramic image is approximately equal to that from two to four intraoral 1275

images, both using state-of-the-art technique (Gibbs, 2000; White and Pharoah, 2014). 1276

1277

4.4.3.3 Cephalometric Radiography. The cephalometric technique provides geometrically 1278

reproducible radiographs of the facial structures. A 2005 to 2006 ADA survey (ADA, 2007), 1279

based on practitioner logs, found 2,733,040 cephalometric images produced annually in private 1280

practices, excluding the military, federal agencies, hospitals, and academic institutions. The 1281

principal application is evaluation of growth and development, as for orthodontic treatment, and 1282

for orthognathic surgery. The equipment provides for standardized positioning of the patient 1283

together with alignment of beam, subject and image receptor. It is frequently useful for the 1284

cephalometric image to show bony anatomy of the cranial base and facial skeleton plus the soft-1285

tissue outline of facial contours. 1286

1287

4.4.3.4 Fluoroscopy. Real-time imaging, or fluoroscopy, is useful only for imaging motion in 1288

structures. Its use should be limited to those tasks requiring real-time imaging, such as the 1289

injection of radiographic contrast fluids for sialography or temporomandibular joint 1290

arthrography. Fluoroscopy requires electronic image intensification and video display to 1291

minimize patient exposure; this equipment is expensive and not usually found in dental facilities. 1292

Furthermore, dental x-ray machines are not generally capable of providing the required 1293

continuous radiation exposure. 1294

1295

Recommendation 33. Fluoroscopy shall not be used for static imaging in dental 1296

radiography. If fluoroscopy is used for dynamic imaging, the practices in NCRP Report 1297

No. 168 shall be followed. 1298

1299

4.4.3.5 Cone Beam Computed Tomography. The CBCT examination is a complementary 1300

modality to, not a replacement for, two-dimensional imaging modalities. Just as for other dental 1301

radiographic examinations, justification for each patient should be based on their imaging history 1302

and the diagnostic yield not achievable with the 2D modalities. The examination is justified if the 1303

anticipated diagnostic yield outweighs the risks associated with radiation (AAOMR, 2008; ADA, 1304


60

2012; EADMFR, 2009; Farman and Scarfe, 2006; White and Pae, 2009). CBCT should only be 1305

used when the question for which the imaging is required cannot be answered adequately by 1306

conventional, lower dose dental radiography, applying the ALARA principle (NCRP, 2003). 1307

This is especially true for CBCT examinations of children (SPR, 2015). 1308

1309

Prior to the acquisition of a CBCT examination, a dental examination by the ordering 1310

provider should be completed, with a review of the patient’s medical history, as well as the 1311

medical and dental imaging history. Previously acquired dental and medical imaging, which falls 1312

short of yielding the necessary clinical information, may justify the need for the CBCT 1313

examination (ADA, 2012; Farman and Scarfe, 2006). The decision for the clinical indication for 1314

CBCT is the professional determination of the treating clinician. Some of the evidence-based 1315

specific indications for CBCT imaging are provided in Section 9.1.5. 1316

1317

4.4.4 Image Viewing Environment 1318

1319

Poor viewing conditions can suppress the clinician’s ability to perceive important diagnostic 1320

information that is present in the image. This may lead to diagnostic errors or unnecessary repeat 1321

examinations in an attempt to produce an “improved” image to compensate for the poor viewing 1322

conditions. It is essential to assure appropriate viewing conditions to insure optimal 1323

interpretation and to avoid repeating adequate images that appear substandard due to substandard 1324

viewing conditions (Kutcher et al., 2006; Patel, 2000). 1325

1326

For maximum diagnostic yield at minimum exposure, image evaluation and interpretation is 1327

best carried out in a quiet atmosphere, free from distractions. With film radiographs, perception 1328

of image details has been shown to be maximum when the illuminated surface of the view box 1329

that is not covered with films or by the opaque film mounts is masked with opaque material to 1330

eliminate glare. View boxes are available that allow for adjusting the luminance and digital 1331

displays allow for adjusting the image brightness and contrast. These view boxes need to be 1332

maintained by periodic cleaning, visual assessment of uniformity and assessment of luminance. 1333

With digital images, perception of image detail is maximized when the illuminated areas of the 1334

display surrounding the digital image are electronically “masked” to reduce glare. 1335


61

1336

When viewing either film radiographs or digital images, reduced ambient (room) light is 1337

required to maximize the perception of image details. As a rule of thumb, the lighting in the 1338

reading area should be at a reduced level but with sufficient light that one can read a newspaper 1339

page. 1340

1341

4.4.4.1 Viewing Conditions for Digital Images. In addition to the general considerations covered 1342

above, the information obtained from all digital images (intraoral, panoramic, cephalometric, and 1343

CBCT) that are viewed on a computer display are subject to a number of conditions, including 1344

those of the viewing environment. Some conditions that may affect specifically the appearance 1345

of the digital display include: 1346

1347

ambient room lighting conditions; 1348

viewing display quality, position and location, settings, calibration, and defects; 1349

reflections of light sources (i.e., overhead lights, windows); and 1350

computer graphics capabilities. 1351

1352

A discussion of optimal configurations for computer and display hardware is beyond the 1353

scope of this report. However, an aspect of image viewing that can have a substantial impact on 1354

the perceived image quality is the room environment where clinical images are viewed and 1355

assessed. While most computer displays can be configured to provide a nominal brightness under 1356

well-lit room conditions, a darkened room environment provides an improved viewing 1357

experience and higher clinical benefit. Pakkala et al. (2012) investigated the effect of ambient 1358

viewing conditions and computer display brand on sensitivity and specificity for diagnosis of 1359

caries. Based on their findings Pakkala et al. recommend that darkened ambient room conditions 1360

be employed, noting that their data suggests that simply increasing the display brightness was not 1361

a recommended alternative. The authors further note that in those practices where clinical images 1362

are routinely displayed chair-side near the patient (and presumably under room conditions 1363

providing a high level of ambient light), it is advisable to confirm diagnosis under subdued 1364

viewing conditions, as their data regarding sensitivity suggest. 1365

1366


62

In the early days of digital imaging, images were presented on cathode ray tube (CRT) 1367

monitors which have largely been replaced by flat-panel displays. A flat panel displays is 1368

composed of a rectangular array of pixels that determine the spatial resolution of the image. 1369

Spatial distortion is not likely, because the pixels are fixed in position, and spatial resolution is 1370

not likely to vary, because the size of the pixels does not change. However, the luminance of the 1371

backlight tends to decrease with time. There are differences between commercial computer 1372

displays and medical grade displays, although some studies have shown comparable diagnostic 1373

efficacy for detecting anatomic sites and common dental pathology (Kallio-Pulkkinen et al., 1374

2014; Tadinada et al., 2015a). 1375

1376

Recommendation 34. Images shall be viewed in an environment adequate to ensure 1377

accurate interpretation. 1378

1379

4.4.5 Use of Radiation Protective Aprons 1380

1381

Radiation protective aprons for patients were first recommended in dentistry many years ago 1382

when dental x-ray equipment was much less sophisticated and image receptors were much 1383

slower than under current standards and when the primary risks were thought to be heritable 1384

effects. They provided protection in an era of poorly collimated and unfiltered dental x-ray 1385

beams. Gonadal (or whole-body) doses from these early full-mouth examinations, reported as 1386

high as 50 mGy (Budowsky et al., 1956), could be reduced substantially by radiation protective 1387

aprons. Gonadal doses from current panoramic or full-mouth intraoral examinations using state-1388

of-the-art technology and procedures do not exceed 5 µGy (White, 1992). A substantial portion 1389

of this gonadal dose results from internal scattered radiation arising within the patient’s head and 1390

body. Technological and procedural improvements have eliminated the requirement for the 1391

radiation protective apron, provided all other recommendations of this Report are rigorously 1392

followed. However, some patients have come to expect the apron and may request that it be 1393

used. Its use remains a prudent but not essential practice. 1394

1395


63

Recommendation 35. The use of radiation protective aprons on patients shall not be 1396

required if all other recommendations in this Report are rigorously followed unless 1397

required by state regulation Otherwise, a radiation protective apron shall be used. 1398

1399

4.4.5.1 Use of Thyroid Collars. The thyroid gland, especially in children, is among the most 1400

sensitive organs to radiation-induced tumors, both benign and malignant (Appendix I). Even with 1401

optimum techniques, the primary dental x-ray beam may still pass near and occasionally through 1402

the gland. If the x-ray beam is properly collimated to the size of the image receptor or area of 1403

clinical interest, and exposure of the gland is still unavoidable, any attempt to shield the gland 1404

would interfere with the production of a clinically-useful image. However, in those occasional 1405

uncooperative patients for whom rectangular collimation and positive beam-receptor alignment 1406

cannot be achieved for intraoral radiographs, then thyroid shielding may reduce dose to the gland 1407

without interfering with image production. 1408

1409

Recommendation 36. Thyroid shielding shall be provided for patients when it will not 1410

interfere with the examination. 1411

1412

1413

4.4.5.2 Maintenance of Protective Aprons and Thyroid Shields. Minimum acceptable evaluation 1414

of radiation protective aprons and thyroid shields consists of periodic visual inspection for 1415

defects. Fluoroscopic evaluation of lead aprons is not recommended as this exposes the inspector 1416

to substantial scattered radiation (NCRP, 2010). 1417

1418

Recommendation 37. Protective aprons and thyroid shields should be hung or laid flat 1419

and never folded, and manufacturer’s instructions should be followed. All protective 1420

shields should be evaluated for damage (e.g., tears, folds, and cracks) quarterly using 1421

visual and manual inspection. 1422

1423


64

4.4.6 Special Considerations for Pediatric Imaging 1424

1425

Children are not small adults. Some tissues in children, including thyroid and female breast, 1426

are two to ten times more sensitive to radiation carcinogenesis than adults, due to higher levels of 1427

cell proliferation, more cells which are less differentiated, and a much longer proliferative future 1428

(Hall and Giaccia, 2011). Additionally, the thyroid gland in children is higher in the neck than in 1429

adults, thus more thyroid tissue is in the radiation field. It is imperative to child-size all radiation 1430

exposures of children commensurate with the diagnostic need of the examination. 1431

1432

Recent studies have suggested that the lens of the eye may be more susceptible to 1433

cataractogenesis than previously thought (ICRP, 2012). The use of leaded glasses has been 1434

shown to significantly reduce the dose to the lens during cone beam CT examinations (Prins 1435

et al., 2011). Thus, leaded glasses should be considered when the orbital and periorbital regions 1436

are not essential to the image (as they might be for pre-orthognathic surgical treatment planning). 1437

1438

It is essential to assure that pediatric patients are not treated as adult patients with regard to 1439

x-ray techniques. The following guidelines should be observed when imaging pediatric patients 1440

(http://imagegently.org/Procedures/Dental): 1441

1442

select x rays for individual’s needs, not merely as a routine; 1443

use the fastest image receptor possible (E- or F-speed film, or a digital receptor); 1444

collimate beam to area of interest; 1445

always use thyroid collars unless it interferes with imaging the needed anatomy; 1446

child-size the exposure time, i.e., optimize the image quality and patient radiation dose; 1447

and 1448

use cone-beam computed tomography only when clinically necessary. 1449

1450

Further information on imaging pediatric patients can be found on the Image Gently website 1451

(http://imagegently.org/Procedures/Dental.aspx). 1452

1453


65

Recommendation 38. Technique factors and selection criteria shall be appropriate to 1454

the age and size of the patient. 1455

1456

4.5 Protection of the Operator 1457

1458

Equipment and procedures that reduce patient exposure will also reduce exposure of the 1459

operator and the environment. Additional measures, however, will further reduce occupational 1460

and public exposure without affecting patient dose or image quality. 1461

1462

4.5.1 Shielding Design 1463

1464

Attention to office layout and shielding design provides convenient methods for 1465

implementing the ALARA principle. Shielding does not necessarily require lead-lined x-ray 1466

rooms. Normal building materials may be sufficient in most cases. Expert guidance can provide 1467

effective shielding design at nominal incremental cost with protection by barriers, distance from 1468

x-ray source, and operator position. 1469

1470

Recommendation 39. Adequacy of facility shielding shall be determined by the qualified 1471

expert whenever the average workload increases by a factor of two or more from the 1472

initial design criteria. 1473

1474

It is in the economic best interest of the dentist to obtain shielding design by a qualified 1475

expert at the facility design stage. For a new or remodeled facility, proper shielding design can 1476

usually provide radiation protection to meet shielding design goals at little or no incremental 1477

construction cost. However, if post-construction measurements indicate that these goals are not 1478

met, the cost of retrofitting may be considerable. 1479

1480

4.5.2 Barriers 1481

1482

Fixed barriers, generally walls, provide the most economical, effective and convenient means 1483

of excluding the public and nonoperator office staff from the primary x-ray beam as it exits the 1484


66

patient or from radiation scattered from the patient or other objects in the primary beam. 1485

Windows (glass, leaded glass or acrylic) in permanent barriers, mirrors, or remote video 1486

monitoring may be helpful. 1487

1488

Barriers are not necessary for protection of the operator of appropriately designed hand-held 1489

x-ray units as these have a nonremovable circular shield built into the device. 1490

1491

Recommendation 40. Shielding designs for new offices with fixed x-ray equipment 1492

installations shall provide protective barriers for the operator. The barriers shall be 1493

constructed so operators can maintain visual contact and audible communication with 1494

patients throughout the procedures. 1495

1496

Recommendation 41. The exposure switch should be mounted behind the protective 1497

barrier such that the operator must remain behind the barrier during the exposure. 1498

1499

4.5.3 Distance 1500

1501

In some existing facilities, design precludes use of a protective barrier. Appropriate distance 1502

and position relative to the position of the x-ray tube and direction of the x-ray beam must be 1503

maintained in these situations. 1504

1505

Recommendation 42. In the absence of a barrier in an existing facility, the operator 1506

shall remain at least 2 m, but preferably 3 m, from the x-ray tube head during 1507

exposure. If the 2 m distance cannot be maintained, then a barrier shall be provided. 1508

This recommendation does not apply to hand-held units with integral shields. 1509

1510

4.5.4 Position of Operator 1511

1512

If the facility design requires that the operator be in the room at the time of exposure, then 1513

the operator should be positioned not only at maximum distance (at least 2 m) from the tube 1514

head, and also in the direction of minimum exposure (Figure 4.1). Maximum exposure will 1515


67

1516

1517

1518

1519

1520

1521

1522

1523

1524

Fig. 4.1. Recommended positions for operator exposing intraoral images of the central 1525

incisors (left) and molars (right). Operator should stand at least 6 feet from the patient and an 1526

angle of 90 to 135 degrees from the central ray (Richards, 1964; White and Pharoah, 2014). 1527

1528

1529


68

generally be in line with the primary beam as it exits the patient. Maximum scattered radiation 1530

will be backwards, i.e., 90 to 180 degrees from the primary beam as it enters the patient. 1531

Generally the position of minimum exposure will be at 45 degrees from the primary beam as it 1532

exits the patient, see Appendix E2 (de Haan and van Aken, 1990). In particular, the operator 1533

should not stand on the side of the patient opposite the x-ray tube as this would expose them to 1534

the direct x-ray beam exiting the patient. 1535

1536

4.5.5 Personal Dosimeters 1537

1538

Monitoring of individual occupational exposures is generally required if it can be expected 1539

that any dental staff member will receive a substantial dose. Occupational Safety and Health 1540

Administration (OSHA) regulations state that individuals who are occupationally exposed to x 1541

rays and who may receive >25 % of the quarterly occupational dose limit, are required to wear a 1542

dosimeter [29 CFR 1910.1096(d)(2)(i)]. NCRP (1998) recommends that personal dosimeters be 1543

provided to all personnel who are likely to receive an effective dose >1 mSv y–1. It must be 1544

emphasized that this recommendation concerns effective dose, which is generally much less than 1545

the dose measured by personal dosimeters. The most recent available data (Table 3.1) indicate 1546

that the average annual occupational dose in dentistry in the United States in 1980 was 1547

0.2 mSv y-1 (Kumazawa et al., 1984) and in Canada from 1970 to 1987 was 0.045 mSv y–1 1548

(Zielinski et al., 2005). Few dental workers received >1 mSv and 68 % received exposures below 1549

the threshold of detection. 1550

1551

World data for the period 2000 to 2002 show a mean annual occupational dose of 0.06 mSv 1552

for dental workers (UNSCEAR, 2008). These data suggest that dental personnel are not expected 1553

to receive occupational exposures greater than the recommended threshold for monitoring of 1554

1 mSv y-1. However, the limit applicable to pregnant workers of 0.5 mSv equivalent dose to the 1555

fetus per month once pregnancy is known suggest that personal dosimetry may be a prudent 1556

practice for pregnant workers. Current regulations require that dosimeters be obtained from 1557

services accredited for accuracy and reproducibility. These services distribute dosimeters 1558

regularly; the facility returns the dosimeters to the service after use (generally monthly or 1559


69

quarterly) for readout and report. The return frequency for personal dosimeters for pregnant staff 1560

should be monthly or more frequent. 1561

1562

Recommendation 43. Provision of personal dosimeters for external exposure 1563

measurement should be considered for workers who are likely to receive an annual 1564

effective dose in excess of 1 mSv. Personal dosimeters shall be provided for declared 1565

pregnant occupationally-exposed personnel. 1566

1567

Recommendation 44. For new or relocated equipment, the facilities shall provide 1568

personal dosimeters for at least 1 y in order to determine and document the doses to 1569

personnel. 1570

1571

Recommendation 45. The facility shall provide personal dosimeters for all new 1572

operators of hand-held dental x-ray equipment for the first year of use. 1573

1574

4.6 Protection of the Public 1575

1576

For shielding design purposes, the public consists of all individuals, including 1577

nonoccupationally exposed staff, who are in uncontrolled areas such as reception rooms, other 1578

treatment rooms, or in adjacent corridors or offices in the building within or outside of the dental 1579

facility (NCRP, 2005). The popular “open design” dental facility, which places two or more 1580

treatment chairs in a single room, may present problems. 1581

1582

Recommendation 46. In dental facilities using large, multi-patient open bay designs, a 1583

patient in proximity to another patient being radiographed shall be treated as a 1584

member of the public for radiation protection purposes. 1585

1586

Recommendation 47. When portable or hand-held x-ray machines are used, all 1587

individuals in the area other than the patient and operator shall be protected as 1588

members of the public. 1589


70

1590

The annual limit on effective dose to a member of the general public, shielding designs 1591

should limit exposure to all individuals in uncontrolled areas to an effective dose that does not 1592

exceed 1 mSv y–1 (NCRP, 2004a; 2004b). 1593

1594

Recommendation 48. New dental facilities shall be designed such that no individual 1595

member of the public will receive an effective dose in excess of 1 mSv annually. 1596

1597


71

5. Quality Assurance and Quality Control 1598

1599

Image quality must strike a balance between providing the information necessary for the 1600

diagnosis and the lowest possible radiation dose. Reducing the dose excessively at the expense of 1601

producing a nondiagnostic image is not a good practice. Conversely, exposing a patient to 1602

excessive dose to produce an esthetically pleasing image beyond that needed for diagnosis is not 1603

a good practice either. The goal is to strike the appropriate balance between a diagnostically 1604

acceptable image and the lowest possible radiation dose. Quality assurance is the planned and 1605

systematic activities necessary to provide adequate confidence that a product or service will meet 1606

the given requirements. Quality control is the routine performance of equipment function tests 1607

and tasks, the interpretation of data from the tests, and the corrective actions taken (NCRP, 1608

2010). 1609

1610

5.1 Image Quality and Patient Dose Optimization 1611

1612

5.1.1 Image Quality 1613

1614

Image quality that is appropriate for the specific diagnostic task is essential in 1615

dental radiography. Reduced image quality can result in missed or unobservable pathology and 1616

lead to misdiagnosis or mistreatment. However, image quality should not be maximized without 1617

regard for patient dose. Digital intraoral receptors, for example, can produce exceptional image 1618

quality at doses that well exceed optimal values. It is essential to optimize the balance between 1619

image quality and patient dose (Section 4.3). This means that image quality and patient dose go 1620

hand-in-hand, especially in digital modalities. In particular, facilities operating with median 1621

doses above the DRL should explore ways that they can reduce their doses, keeping in mind that 1622

the images must be clinically acceptable (Section 4.2). However, being below the appropriate 1623

DRL, by itself, does not imply that doses have been fully optimized. 1624

1625

The older technology of film-based imaging provided a built-in means for limiting dose: 1626

excessive exposure to the film would generally result in a film so optically dense, or dark, that it 1627

is virtually useless for diagnostic purposes. Under-development of film (low developer 1628


72

temperature or improper replenishment of developer solution) will result in excessive patient 1629

doses and poor image quality (low contrast). 1630

1631

Solid state image receptors can offer a reduction in radiation required to produce an image 1632

(Anissi and Geibel, 2014). Patient skin entrance dose per image can be reduced from ~100 µGy 1633

with F-Speed film to ~40 to 80 µGy with a solid state receptor (Table 6.1) while still producing 1634

diagnostically acceptable images. Surveys have shown, however, that many solid state receptors 1635

are using doses similar to or higher than D-speed film (Walker et al., 2014).1 This has been 1636

primarily attributed to the dentists not changing their x-ray techniques when switching from film 1637

to digital solid state receptors. In addition, Farman and Farman (2005) have shown that 1638

practitioners are using 1.5 to 20 times the exposure necessary to produce a diagnostically useful 1639

image. This overexposure is then compensated for by the digital imaging system software, 1640

thereby providing no indication of overexposure to the user. In addition, it is advisable for the 1641

clinical practice to become familiar with the exposure response of the particular digital system 1642

they implement in order for the patient to benefit from the reduced exposures associated with 1643

digital imaging. 1644

1645

An additional problem with the use of solid state receptors is a consequence of their ease and 1646

speed of use, which make retakes easy and fast. This can result in multiple image acquisitions 1647

and total patient doses greater than when film is used (Berkhout, 2003). Therefore, it is critically 1648

important that repeat images be obtained only when absolutely needed for diagnostic purposes. 1649

1650

Give the rapidly advancing technology of image receptors, with increasing receptor speed, it 1651

is important that newly purchased x-ray machines be able to correctly expose such receptors. 1652

1653

Recommendation 49. X-ray machines should provide a range of exposure times suitable 1654

for twice the speed of the fastest available image receptors. 1655

1656

1 Gray, JE (2015). Personal Communication. (DIQUAD, LLC, Steger Illinois)


73

5.1.2 Patient Dose 1657

1658

Patient doses can be controlled or optimized using many techniques. The speed of the image 1659

receptor is the most important. For example, the use of F-Speed film or digital receptors in place 1660

of D-Speed film can reduce the dose to the patient by ~50 % or more in intraoral imaging. In 1661

panoramic and cephalometric imaging, use of rare-earth screen-film combinations or digital 1662

receptors allows for substantial reduction of patient dose. 1663

1664

Film processing requires careful attention to the concentration and temperature of the 1665

solutions and the time the films spends in each solution. Improper processing can render a 1666

properly exposed image nondiagnostic and useless. It can also lead to an increase in patient 1667

radiation dose—as the developer solution is depleted the x ray exposure time must be increased 1668

to obtain appropriate film density. 1669

1670

In addition to receptor speed, use of rectangular collimation in intraoral imaging reduces the 1671

effective dose to the patient by an additional 80 % (Ludlow, 2008). As an added bonus, 1672

rectangular collimation reduces scatter and improves image quality. 1673

1674

In CBCT imaging, a variety of factors are available to reduce patient dose, including field-of-1675

view, milliampere-seconds, voxel size, and spatial resolution, 360 versus 180 degree movement, 1676

and avoiding the use of machine exam presets such as high definition (HD) only when necessary. 1677

These must be selected judiciously with diagnostic objective and patient dose in mind. 1678

1679

5.1.3 Technique Charts 1680

1681

Regardless of image receptor speed, another method to insure image quality, while reducing 1682

patient dose, is the utilization of size-based technique charts. Technique charts should be 1683

developed for each x-ray unit and image receptor combination. These should include technique 1684

settings for specific anatomical areas in combination with the patient size (small, medium, large) 1685

for adults and children. These should be developed for both intraoral and extraoral imaging, 1686

listing the exam, patient size, along with adult and pediatric settings, and image receptor (film 1687


74

type, digital image receptor). It is not adequate to use equipment manufacturer technique charts 1688

without validation. Technique charts should be posted conveniently near the control panel where 1689

the technique is adjusted for each x-ray unit. With digital workstations, technique charts may 1690

also be readily placed on the workstation’s desktop. When the x-ray unit is replaced, or an image 1691

receptor is added, the chart must be updated (see Section 6.3.2.4 for further information on 1692

technique charts). 1693

1694

5.2 Quality Control 1695

1696

Quality control (QC) is an integral component of a quality assurance (QA) program. As 1697

noted above QA is the overall program for assuring quality outcomes. QC, on the other hand, is 1698

the part of the QA program that employs regular physical testing designed to detect changes in a 1699

radiographic system before they can interfere with diagnostic performance. Lack of a quality 1700

control program often results in poor quality images, lacking clinically necessary details for 1701

diagnostic purposes, increasing radiation doses to the patient and staff, and repeated images 1702

resulting in increased radiation dose. 1703

1704

The QC program for each facility must be customized to the imaging modalities in use, the 1705

staffing capabilities and equipment available. The QC program should be established in 1706

consultation with the qualified expert, documenting specific QC activities, the personnel 1707

responsible for performing each activity (e.g., dental assistant, qualified expert), procedures to be 1708

followed for each activity, acceptable ranges of results, and actions to be taken when results of 1709

any QC activity are not within the acceptable range. Such a program includes daily, weekly, 1710

monthly, quarterly, and annual tests of the various components of the imaging chain. In general, 1711

QC activities that should be performed frequently do not entail complex equipment or 1712

procedures and can be performed by on-site dental assistants or other technical staff. More 1713

complex tasks or those requiring specialized training or equipment should be performed by the 1714

qualified expert at intervals consistent with the probability of undetected failure, the impact of 1715

failure on patient care, and the availability of the qualified expert. 1716

1717


75

All dental facilities utilizing x-ray imaging should be evaluated initially (acceptance testing, 1718

also known as initial equipment performance evaluation) and periodically thereafter by a 1719

qualified expert. This will assure that the image quality and the patient radiation dose are 1720

appropriate, persons in the vicinity of the x-ray equipment are safe, regulatory compliance is 1721

maintained, and that the facility staff is maintaining their portion of the quality control program. 1722

1723

No matter what image receptor is used, the QC program should include periodic testing and 1724

calibration of the x-ray system in order to see that tube-head stability, collimation, tube potential, 1725

half-value layer, exposure time, output reproducibility, and other factors are within the 1726

appropriate tolerances. Once it is ascertained that the x-ray unit is functioning properly, the 1727

image receptor can be evaluated using this calibrated x-ray unit for test exposures. 1728

1729

5.2.1 Radiation Measurements of X-Ray Producing Diagnostic Dental Equipment 1730

1731

The qualified expert is the individual who is responsible for, and qualified to measure 1732

radiation dose, interpret the results, and advise on the clinical implications of dose and image 1733

quality in imaging facilities, including dental facilities. While measuring radiation dose may 1734

appear a simple task, the qualified expert must be familiar with many complex technical factors 1735

when measuring and evaluating dose in dental facilities. Different types of radiation detectors are 1736

suited to different types of radiation measurements, and different units of measure are used for 1737

different modalities. For example, a radiation detector that is suitable for measuring entrance 1738

skin exposure in dental radiography may or may not be suitable for measuring dose in a CBCT 1739

system, depending on the units used and the comparisons to be made. Measurements of exposure 1740

to persons in the vicinity of an x-ray producing device must be made with an entirely different 1741

type of radiation detector. Both types of radiation measurement are required for regulatory 1742

compliance in many jurisdictions. 1743

1744

When changing from film to digital imaging, the settings used for film will typically deliver 1745

unnecessarily high radiation to the patient, often by a factor of two or more. Hence, the qualified 1746

expert should be consulted before converting to digital image receptors, so that the exposure 1747

factors may be reduced before commencing patient imaging. The manufacturer may provide 1748


76

suggestions for technique factors, but only the qualified expert has the knowledge and equipment 1749

needed to accurately measure radiation dose, interpret those data, and to advise the dental 1750

practitioner about the appropriate technique factors to be used with a new digital receptor. 1751

1752

While service engineers can perform radiation measurements in dental imaging facilities, 1753

their results do not replace the testing by a qualified expert. 1754

1755

5.2.2 Phantoms for Quality Control and Dose Measurements 1756

1757

There are a limited number of imaging phantoms that are designed specifically for dental 1758

imaging. When these are not readily available, the qualified expert may adapt conventional 1759

radiography phantoms that are appropriate to the field size and image quality considerations 1760

relevant to dental radiography. 1761

1762

The FDA requires that phantoms be provided by the CBCT manufacturer to assess specified 1763

image quality indicators. Conventional head CT phantoms for image quality and dose 1764

measurements (CTDI) may be used if considered appropriate by the qualified expert. Dose 1765

measurements may also be made in air, without the use of a phantom. Some equipment 1766

manufacturers may provide tabulation of dose-area product for equipment capable of CT-like 1767

imaging. 1768

1769

Recommendation 50. A suitable radiographic phantom shall be used to optimize 1770

radiation dose and image quality, and for continuing quality control measurements. 1771

1772

5.2.3 Quality Control for Film Imaging 1773

1774

For facilities using film-based radiography, the greatest single source of image variability is 1775

film processing. The facility QC program should follow the film processor manufacturer’s 1776

recommendations for quality control. The most critical element of film processing quality control 1777

(whether hand developing or using an automatic film processor) is to assure that the processing 1778


77

chemistry is maintained at the specified temperature (appropriate for the processing time), 1779

remains fresh (i.e., undiluted and uncontaminated), is replenished daily, and replaced regularly. 1780

1781

Film processing solutions are subject to gradual deterioration. The deterioration may go 1782

unnoticed until it becomes severe enough to degrade image quality and require an increase in 1783

exposure time, thus increasing patient dose. Daily measurements are required to prevent this 1784

degradation. 1785

1786

A baseline radiographic image is first produced using fresh solutions at proper temperatures. 1787

A standardized test object [step wedges are commercially available or can be assembled from 1788

discarded lead foil from film packets (Valachovic et al., 1981; White and Pharoah, 2014)] is 1789

placed on the film, exposed, and processed to produce this baseline image. Subsequent images 1790

are produced daily under identical conditions. The follow-up images are compared to the 1791

baseline images and corrective actions are taken if changes in the image quality are noted. The 1792

images are saved for later reference, and records are maintained of any image technical factors 1793

that are measured and any changes or repairs that are made. 1794

1795

Film processing quality control is essential to maintaining optimum quality radiographic 1796

images and assuring patient doses are as low as reasonably achievable. This is required by some 1797

state radiation protection agencies. 1798

1799

Whether using manual- or automatic-film processing, the specified development time and 1800

temperature must be used. If manually processing films, the films must be agitated during 1801

processing according to the film manufacturer’s instructions. 1802

1803

Developer and fixer solutions must be replenished with eight ounces of appropriate solutions 1804

each day before processing patient films (solutions must be stirred to assure the new solutions 1805

are mixed thoroughly with the older solutions). All solutions should be drained, the tanks 1806

cleaned, and refilled with fresh solutions at least every two weeks. 1807

1808


78

The water in the wash tank should be changed daily or after every 30 intraoral films that are 1809

processed, whichever occurs first. For higher volumes or larger films, such as panoramic or 1810

cephalometric, the water should be changed more frequently. 1811

1812

Recommendation 51. Film processing quality shall be evaluated daily, before processing 1813

patient films, for each film processor or manual processing system. 1814

1815

Quality control for film processing is an essential part of assuring optimum film quality while 1816

minimizing radiation dose to the patients and staff. The tests and tasks (Table 5.1) are easy to 1817

carry out and take very little time. 1818

1819

5.2.4 Quality Control for Digital Imaging Receptors 1820

1821

It is important to make sure that the quality of the digital images produced with any type of 1822

image receptor is adequate for diagnostic purposes. Often the quality of the images from the 1823

image receptors or storage phosphor plates are evaluated subjectively, thereby leading to the 1824

possibility that there is no consistency in determining when a storage phosphor plate should be 1825

replaced, when a digital image receptor has been damaged, or the image quality has deteriorated. 1826

Studies have shown that objective evaluation of some critical parameters such as spatial 1827

resolution, contrast detail detectability, and dose-response curve over a wide range of exposures 1828

can be used to confirm the quality of the images made from storage phosphor plates or traditional 1829

digital image receptors. A typical QC phantom for dental digital imaging systems is shown in 1830

Figure 5.1. 1831

1832

While there is no clear standard on how often image quality must be tested on different 1833

digital imaging systems it is recommended to test after 40 exposures on storage phosphor plates 1834

and once every three months for digital image receptors using a phantom which is capable of 1835

testing critical characteristics like spatial resolution, contrast, freedom from artifacts and dead 1836

pixels, and dose response over a wide range of exposures. 1837

1838


79

1839

TABLE 5.1—Frequency of quality control testing for film-based radiography.a 1840

QC Task Frequency Who

Darkroom fog At least annually and when fog is

suspected

Office staff

Developer and fixer replenished with

solution recommended by

manufacturer

Daily Office staff

Change developer and fixer solutions Every two weeks or more frequently

for a busy practice

Office staff

Developer, fixer, wash temperature Check daily before processing films Office staff

Change water in wash tank Daily

If more than 30 films per day, then

after every 30 films

Office staff

X-ray machine performance Not to exceed every 4 y. Annually is

ideal

Qualified expert

1841

aFor more detail, the reader is referred to Appendix A. 1842

1843


80

1844

1845

1846

Fig. 5.1. A phantom for measuring image quality in intraoral digital radiography, constructed 1847

of tissue-equivalent Lucite with test objects imbedded internally. When the position-indicating 1848

device is placed on the four plastic rest tabs as shown, the geometry of intraoral digital 1849

radiography is simulated. 1850

1851


81

There are a few activities that can assist in maintaining a quality digital imaging system. For 1852

PSP-based devices, these include cleaning the sensor plate surface and the transport assembly 1853

regularly and when artifacts are observed (using only cleaners recommended by the 1854

manufacturer), and replacing the plates when they become damaged or stained. For many 1855

technical problems the only course of action is a service visit. Some manufacturers also 1856

recommend that certain mechanical parts within the scanner be replaced every 2 to 4 y. Although 1857

not an aspect of routine quality control, a means for ensuring that the PSP plates are exposed on 1858

the correct side is recommended, given the ease with which a PSP image receptor may 1859

accidentally be exposed on the opposite side, leading to the potential for incorrect viewing and 1860

clinical evaluation. Another issue with PSP plates is the propensity for scratching and fraying of 1861

the edges during handling. Damaged plates must be replaced in order to maintain quality 1862

imaging. 1863

1864

A quality control program can reduce patient dose while optimizing diagnostic quality 1865

images. Figure 5.2, which comes from a study examining implementation of a digital QC 1866

program in private dental offices, demonstrates this well. 1867

1868

5.2.5 Quality Control for CBCT 1869

1870

Facilities utilizing CBCT imaging should follow the imaging equipment manufacturer’s specific 1871

instructions for quality control. CBCT manufacturers are required by the Federal Performance 1872

Standard [21 CFR 1020.33(c)(3)(d)] to provide a CBCT QC manual and appropriate phantom 1873

that evaluates specified elements of image quality. If a CBCT system has been installed without 1874

such a quality assurance manual and phantom, the dental practitioner or administrator should 1875

contact the CBCT manufacturer to obtain the required QC manual and phantom. Both the QC 1876

manual and phantom are essential elements of the QC program. A typical QC phantom for dental 1877

CBCT systems is shown in Figure 5.3 (some phantoms are available with software to analyze the 1878

CBCT QC images). 1879

1880


82

1881

1882

Fig. 5.2. Distribution of skin exposures before and after quality control (adapted from Walker 1883

et al., 2014). The average skin exposure is substantially reduced after a quality control program 1884

is implemented. 1885

1886

For further detail, the reader is referred to Appendix B. 1887

1888


83

1889

1890

1891

1892

1893

1894

1895

1896

1897

1898

Fig. 5.3. A typical dental CBCT phantom for quality measurements, constructed of tissue-1899

equivalent plastic or similar material, and with imaging test objects embedded internally. It is 1900

placed in the machine where the patient’s head would be and then exposed to measure the 1901

various characteristics of the acquired volume. 1902

1903


84

1904

5.2.6 Quality Control for Image Displays 1905

1906

Since digital radiographs are viewed on a computer display, the display must be calibrated 1907

and evaluated. Digital radiographs should be viewed with the center of the display positioned 1908

slightly below eye level. Subdued lighting should be used and every effort should be made to 1909

eliminate glare and reflections from extraneous sources of light such as room lights, view boxes, 1910

and windows. 1911

1912

It is essential that the computer display used to view digital dental images be properly 1913

calibrated in terms of brightness and contrast. The Society of Motion Picture and Television 1914

Engineers (SMPTE) test pattern (Figure 5.4) is almost universally available in the medical 1915

imaging community for this purpose. This pattern should be available on the digital imaging 1916

system, i.e., stored on the computer hard drive. If not, the vendor or manufacturer should be able 1917

to provide a copy. It is also readily available on the internet. 1918

1919

The brightness and contrast controls are adjusted to obtain a display image similar to those in 1920

Figures 5.2. Of particular importance are the 0 % and 95 % patches which are inset in the 5 % 1921

and 100 % squares of the test pattern. Both of these should be visible when the window width is 1922

set to encompass the maximum pixel range for the computer system, usually 0 to 255. 1923

1924

The SMPTE pattern also provides high contrast (black and white) and low contrast resolution 1925

patterns in the center and four corners. The mid-gray cross hatch pattern can be used to measure 1926

distortion of the display from image processing software and for older cathode ray tube (CRT) 1927

displays. 1928

1929

5.2.7 Quality Control Tests and Frequency for Digital Radiography 1930

1931

Quality control tests must be carried out regularly and the results documented. Most of these 1932

tests (Table 5.2) take very little time but assure the quality of the digital radiographic images. 1933

1934


85

1935

1936

1937

1938

1939

1940

1941

1942

1943

1944

Fig. 5.4. Society of Motion Picture and Television Engineers (SMPTE) test pattern provides 1945

a standard image for calibration and evaluation of computer displays. Left arrow— 0 % patch in 1946

5 % square; right arrow— 95 % patch in 100 % square (Gray, 1985). 1947

1948


86

TABLE 5.2—Frequency of quality control tests for digital radiography. 1949

QC Task Frequency Who

X-ray machine performance:

Intraoral, panoramic, cephalometric

Not to exceed every 4 y. Annually is

ideal.

Qualified expert

X-ray machine performance: CBCT Every 1 – 2 y Qualified expert

Display Performance Quarterly Staff (using SMPTE

Test Pattern)

Evaluate images from PSP plates for

artifacts

Visually inspect CR plates with each

use

Evaluate each image for artifacts

Staff

Evaluate digital sensor images for

artifacts

Evaluate each image for artifacts Staff

Evaluate junction between cable and

sensor

Daily Staff

Phantom test PSP plate performance Every 40 exposures per plate Staff

Phantom test CCD or CMOS sensor Quarterly for each sensor Staff

1950


87

5.3 Infection Control 1951

1952

Dental radiologic procedures are conducted using universal precautions that prevent transfer 1953

of infectious agents among patients, operator, and office staff. All equipment and procedures 1954

should be compatible with current infection control philosophy and techniques, while still 1955

maintaining the ALARA principles. It is important that a rigorous, written infection control 1956

policy be developed and routinely applied. These practices apply especially to intraoral 1957

radiography, in which multiple projections are commonly used in a single examination. The 1958

image receptors are placed in a contaminated environment. Gloved hands of the operator who is 1959

observing universal precautions can become contaminated when placing image receptors in the 1960

mouth or removing exposed ones from the mouth. This contamination then can be easily spread, 1961

such as to the x-ray machine and to image processing equipment. Universal precautions are 1962

mandated by the Occupational Safety and Health Administration to prevent dissemination of 1963

contamination (OSHA, 2015). Details for dental imaging infection control procedures can be 1964

found in most oral and maxillofacial radiology textbooks (White and Pharoah, 2014). 1965

1966

Recommendation 52. There shall be an infection control policy to protect staff and 1967

patients that encompasses imaging equipment and procedures. 1968

1969

Recommendation 53. Imaging equipment and devices should be designed to facilitate 1970

standard infection control precautions. 1971

1972


88

6. Image Receptors 1973

1974

6.1 Direct Exposure X-Ray Film 1975

1976

6.1.1 General Information 1977

1978

Patient doses for intraoral film radiography have decreased dramatically since 1920 (Figure 1979

6.1). In fact, the doses today are ~1 % of that used in the early twentieth century (Richards and 1980

Colquitt, 1981). 1981

1982

Since the mid-1950s the most common image receptors for intraoral radiography in the 1983

United States has been direct exposure film of American National Standards Institute (ANSI) 1984

Speed Group D (Goren et al., 1989; Platin et al., 1998). Faster films, ANSI Speed Group E, were 1985

introduced in the early 1980s, with improved versions coming in the mid-1990s. These faster 1986

films have been widely used in Europe (Svenson and Petersson, 1995; Svenson et al., 1996). 1987

Published data show that these faster films provide for patient and staff dose reductions of up to 1988

50 %. However, early E-speed films exhibited decreased contrast and higher sensitivity to 1989

processing conditions than were found with D-speed films (Diehl et al., 1986; Thunthy and 1990

Weinberg, 1982). These problems have been corrected and presently E-speed film can be used 1991

with no degradation of diagnostic information (Conover et al., 1995; Hintze et al., 1994; 1996; 1992

Kitagawa et al., 1995; Ludlow et al., 1997; Nakfoor and Brooks, 1992; Price, 1995; Svenson 1993

et al., 1997a; Tamburus and Lavrador, 1997; Tjelmeland et al., 1998). Digital image receptors 1994

with speeds similar to or faster than E-speed film are available. Intraoral films of speed group F 1995

are commercially available, perform at the same diagnostic levels as both D- and E-speed films 1996

and are suitable for routine use (Farman and Farman, 2000; Ludlow et al., 2001; Thunthy, 2000). 1997

(One manufacturer produces an E-F-speed film. It is E-speed when hand processed and F-speed 1998

when machine processed.) In spite of the fact that use of E and F speed film was a shall 1999

statement in NCRP Report No. 145 (NCRP, 2004), the most recent study of the relative use of D 2000

and F speed films in the United States showed that 78 % of film users continue to use D-speed 2001

film (NEXT, 2015). In fact, D-speed film requires the same exposure to the patient as it did in 2002

2003


89

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

Fig. 6.1. Approximate relative exposures at skin entry for intraoral radiographs, 1920 to 2016

2000. Arrows indicate introduction of faster films (ANSI speed groups A, B, C, D, E and F, as 2017

indicated). The solid line represents smoothed best fit to the data points, illustrating the 2018

exponential downward trend of exposures over time. The exposure required for F-speed film is 2019

~1 % of that required for the first dental films, and 50 % of that required for D-speed film 2020

(Farman and Farman, 2000). 2021


90

1955 (red circle, Figure 6.1). Studies in the United Kingdom show that only a very small 2022

minority of facilities using film for intraoral imaging use D-speed film (Holroyd, 2013). 2023

2024

Film users are urged to update their techniques and technique charts as they adopt faster 2025

image receptors. It is incumbent on manufacturers to assist users in establishing new techniques. 2026

2027

Recommendation 54. Image receptors of speeds slower than ANSI Speed Group E-F 2028

film shall not be used for intraoral radiography, i.e., D-speed film shall not be used. 2029

2030

6.1.2 Equipment and Facilities 2031

2032

After exposure, radiographic film must be processed to produce a diagnostic image. The 2033

equipment and facilities which are needed to process intraoral films must be optimized in order 2034

to generate the diagnostic image. A perfectly placed and exposed film can easily be rendered 2035

nondiagnostic by poor processing. 2036

2037

6.1.2.1 Darkroom. Each darkroom should be evaluated for light leaks and safelight performance. 2038

A “coin test” is performed by placing an unexposed, unwrapped intraoral film at a normal 2039

working position and putting a coin upon it. After 2 min, the film is processed. An image of the 2040

coin indicates a problem with either light leaks or the safelight. Repeating the procedure with the 2041

safelights off will determine if the fog is due to the safelights or light from outside the darkroom. 2042

These tests are should be performed at least quarterly, and preferably monthly (White and 2043

Pharoah, 2014) or following a change in the safelight filter or bulb, or other changes to the 2044

darkroom that could affect its integrity. Direct exposure films have different spectral sensitivities 2045

from those used with screens; a safelight filter appropriate for one may not be adequate for the 2046

other. In addition, the film used with screens must be pre-exposed in the cassette to produce a 2047

uniform, mid-gray density when processed in order to carry out this test. 2048

2049

Daylight loaders are commonly used with automatic dental film processors, eliminating the 2050

need for the darkroom. These systems provide light-tight boxes attached to the processor. Each 2051

box contains a port for placing exposed films (still in their wrappers or cassettes) in the box, 2052


91

ports for inserting the hands so the operator may manipulate films in the box, and a viewing port 2053

through a filter similar to the safelight filter. The processor safelight filter is designed for use in a 2054

room with low-level illumination. It may be necessary to use daylight loaders only in rooms with 2055

reduced illumination. Furthermore, the daylight loader may present difficulties in infection 2056

control with intraoral film wrappers contaminated with oral fluids. Like the darkroom, the 2057

daylight loader may be evaluated for light leaks using the “coin test” (AAPM, 2015). 2058

2059

Recommendation 55. Each darkroom and daylight loader shall be evaluated for fog at 2060

initial installation, and then at least quarterly and following change of room lighting or 2061

darkroom safelight lamp or filter. 2062

2063

6.1.2.2 Storage of Radiographic Film. It is essential to protect radiographic film in storage from 2064

radiation exposure. Radiographic film used in film-screen imaging is less sensitive to direct 2065

radiation exposure today than in the past (Suleiman et al., 1995). 2066

2067

Recommendation 56. Film, including film in cassettes, shall not be exposed to excessive 2068

radiation during the period it is in storage. 2069

2070

6.1.2.3 Film Processors. Film processing is a sequence of chemical reactions that are time and 2071

temperature dependent. Processing solutions must be at the proper concentrations. Solutions that 2072

are either dilute, excessively concentrated, or contaminated will degrade the image quality. Even 2073

with proper solution concentrations and temperatures, film processing depends on a proper 2074

combination of time and temperature. Deviations from proper processing will result in films that 2075

are of reduced contrast, and are either too light or too dark. In addition, poor processing quality 2076

commonly will result in higher radiation doses to the patient as the exposure time will be 2077

increased to obtain a film dark enough to view. 2078

2079

Recommendation 57. Film shall be processed with active, properly replenished 2080

chemicals, and time-temperature control, according to manufacturers’ 2081

recommendations. 2082

2083


92

6.2 Screen-Film Systems 2084

2085


2087

Extraoral exposures, such as for panoramic and cephalometric radiography, utilize light-2088

sensitive film in combination with intensifying screens within a cassette. The film sensitivity 2089

must be spectrally matched to the spectrum of light emitted from the intensifying screens. 2090

2091

The intensifying screens consist of thin layers of phosphor crystals that fluoresce when 2092

exposed to x rays. The film is exposed by light emitted by the intensifying screens. Absorption of 2093

light emitted from the intensifying screens is increased by the addition of dyes to the film 2094

emulsion. The spectrum of light most readily absorbed by the film must be matched to the 2095

spectrum of light emitted by the intensifying screens. 2096

2097

Screen-film systems are widely available with varying speed, contrast, and latitude 2098

characteristics, depending on specific imaging needs. Screen-film combinations are more 2099

sensitive to x rays than direct exposure x-ray film, thus reducing the level of exposure to the 2100

patient. Image sharpness, however, is decreased as a result of diffusion of light emitted from the 2101

intensifying screens to expose the film. 2102

2103

Rare-earth intensifying screens, used in conjunction with properly matched film, are the 2104

fastest screen-film combinations available. Rare-earth screens that emit green or blue light are 2105

more efficient at absorbing radiation that exits the patient and converting x-ray energy to light 2106

energy than the blue-emitting calcium tungstate screens. Patient exposure in panoramic and 2107

cephalometric radiography may be reduced by ~50 % using fast rare-earth versus slower calcium 2108

tungstate screen-film combinations with no significant difference in perceived diagnostic quality 2109

(Gratt et al., 1984; Kaugars and Fatouros, 1982). Use of screen-film systems with flat grain 2110

technology results in increased film speed without a loss of image sharpness. Rare-earth imaging 2111

systems using this film have been shown to be 1.3 times faster than a comparable system using 2112

conventional film emulsion technology without compromising diagnostic quality (D’Ambrosio 2113

et al., 1986; Thunthy and Weinberg, 1986; White and Pharaoh, 2014). 2114


93

2115


2117

Equipment and facilities for screen-film systems are the same as for direct exposure film 2118

(Section 6.1.2). 2119

2120

6.2.2.1 Care of Screen-Film Systems for Film-Based Cephalometric and Film-Based Panoramic 2121

Imaging. Both cassettes and screens may acquire defects during normal use. Integrity of cassettes 2122

is determined by visual inspection and by processing of an unexposed film that has been in the 2123

cassette for at least 1 h while the cassette is exposed to normal room illumination. Light leaks 2124

from the cassette will appear as dark areas or streaks on the film. Screens are evaluated visually 2125

for surface defects such as scratches or fingerprints. Screens should be cleaned periodically, 2126

following the manufacturer’s instructions. 2127

2128

Poor screen-film contact leads to unsharpness in images. Screen-film contact and uniformity 2129

of response are best evaluated by exposing a film (in its cassette) overlaid with a piece of copper 2130

test screen. Visual inspection of the processed film for sharpness and uniformity of the image can 2131

assess performance of the imaging system. Unsharp areas will appear as darker areas on the 2132

image. This is a test the qualified expert can carry out during the periodic evaluation. 2133

2134

6.2.2.2 Screen-Film Speed Recommendations. It is important to use the fastest possible screen-2135

film combination that provides the necessary diagnostic information when acquiring panoramic 2136

and cephalometric images. 2137

2138

Recommendation 58. Screen-film systems of speeds slower than ANSI 400 shall not be 2139

used for panoramic or cephalometric imaging. Rare-earth systems shall be used. 2140

2141


94

6.3 Digital Imaging Systems 2142

2143


2145

Digital radiography involves the acquisition of a digital image consisting of a two-2146

dimensional array of pixels. In direct digital radiography, the latent image is directly recorded by 2147

a suitable sensor. Receptors used in direct digital radiography are photostimulable storage 2148

phosphor plates (PSP) or solid state electronic devices containing either charge-coupled device 2149

(CCD) or complementary metal-oxide semiconductor (CMOS) technology. At times it is 2150

necessary to convert a film image into a digital image—this is referred to as indirect digital 2151

radiography. The resultant electronic image may be presented on a computer display, converted 2152

to a hard copy image, or transmitted electronically. For a historical overview of digital imaging 2153

in dentistry see Appendix C. 2154

2155

6.3.1.1 Proportion of Digital versus Film, Proportion of PSP versus CMOS-CCD. Preliminary 2156

analysis of the data from the 2015 NEXT Dental Survey shows 87 % of the sites surveyed used 2157

digital acquisitions (70 % sensors; 19 % PSP) for intraoral imaging versus 11 % for film. Of 2158

those sites using film, 78 % used D-Speed film and 22 % used F-Speed film. Only 1.2 % of all 2159

sites surveyed used rectangular collimation. 2160

2161

6.3.1.2 Advantages of Digital Imaging Compared to Film Imaging. There are numerous 2162

recognized advantages that digital-based imaging provides over film. Many of the advantages are 2163

very similar to those observed in general radiology such as the elimination of darkroom film 2164

processing, the ability to digitally manipulate images, and the ability to easily store and transmit 2165

copies of patient images. There are also advantages specific to dental radiography. 2166

2167

Recent improvements in the quality of images provided by digital-based image receptors for 2168

dental radiography have permitted the capture of dental x-ray images that provide comparable 2169

clinical value as that for film (Alkurt et al., 2007). From an image quality standpoint the benefits 2170

of digital imaging are numerous. Farman and Farman (2005) published a study of the imaging 2171

characteristics for a number of digital x-ray technologies for dentistry. Their results show a broad 2172


95

range of values for spatial resolution over wide exposure ranges. The majority of systems (some 2173

with more than one configuration) have spatial resolutions >10 cycles per millimeter (c mm–1). 2174

Huda (2010) reported that the human can resolve ~5 c mm–1 at 25 cm, and ~30 c mm–1 at close 2175

inspection. Therefore while film still retains a lead regarding spatial resolution (~20 c mm–1), the 2176

visualization of clinically relevant image detail using digital technology is likely now 2177

comparable to that for film under typical viewing conditions. 2178

2179

Digital images can be modified by a variety of image processing techniques ranging from 2180

simple enlargement of the image to manipulations of image characteristics such as contrast, 2181

sharpness and ransom noise. 2182

2183

The practice of x-ray imaging should include the optimization of equipment and procedures 2184

to minimize radiation dose to the patient while providing image quality that accomplishes the 2185

clinical task. Digital image receptors can provide acceptable images at patient exposures well 2186

below those for film (Section 5.1). 2187

2188

The following summarizes the advantages of digital imaging in dental radiography compared 2189

with film-based imaging: 2190

2191

acceptable image quality at reduced patient x-ray dose; 2192

post processing image manipulation including contrast, density, and edge sharpness; 2193

the ability to make measurements from the image; 2194

3D reconstruction from CBCT acquisitions; 2195

elimination of the darkroom and film processing; 2196

reduction in time spent making radiographs; 2197

space-efficient storage; 2198

teleradiology; and 2199

environmentally friendly, chemical-free imaging. 2200

2201

6.3.1.3 Potential for Dose Reductions for PSP and DR Compared with Film. Like any x-ray-2202

based imaging modality, the clinical benefits of the modality must be weighed against the 2203


96

associated risks. The x-ray system should be optimized to provide the required clinical benefit at 2204

the lowest possible radiation dose. Film used for dental intraoral radiography is directly exposed 2205

by the x-ray beam. Consequently, this direct film exposure results in a tenfold or greater 2206

radiation dose to the patient compared with screen-film combinations as used in panoramic and 2207

cephalometric imaging. 2208

2209

Dental film manufacturers have provided film types of several speed classes with differing 2210

image quality and dosimetric properties. A NEXT survey of dental facilities in 1999 found 2211

median patient entrance air kerma for routine bitewing films to be 1.6 mGy (maximum of 2212

5.5 mGy) for D-speed class film, and 1.2 mGy (maximum of 2.9 mGy) for E-speed class film 2213

(Moyal, 2007). Direct digital and PSP-based image receptors can provide useful clinical images 2214

at substantially lower entrance doses (Table 6.1). 2215

2216

Farman and Farman (2005), documented the ability of most tested, commercially available 2217

digital systems to provide images of acceptable image quality at lower entrance air kerma and a 2218

greater exposure latitude compared to film. This improved x-ray efficiency and the ability to 2219

digitally enhance images can allow images that might be otherwise considered to be under-2220

exposed to still provide clinical value. 2221

2222

With digital imaging systems, there is a significant potential for dose reduction compared 2223

with film-based imaging. Corresponding to the decrease in exposure time, the patient dose for 2224

PSP systems is reduced to approximately one-half or less compared to film. The main issues in 2225

digital technology are positioning errors. The size and rigidity of the image receptors, especially 2226

CCD sensors, can make them uncomfortable for the patient and difficult to accurately position 2227

compared with film packets. Combined with the ease of repeating an image, this can lead to 2228

many additional exposures and a concomitant increase in the total radiation dose to the patient, 2229

despite the reduced radiation dose per image. 2230

2231


97

2232

TABLE 6.1—Typical dental bitewing skin entrance dose ranges. 2233

aGray, J.E. (2015). Personal communication (DIQUAD, LLC, Steger, Illinois) 2234

bBased on 25th and 75th percentile of optimal exposure from Table II from Udupa et al. (2013). 2235

Note—Required exposure for optimal image quality varies with digital image receptor type. Table 6.1 2236

should be considered as a starting point for image quality and dose optimization. 2237

2238

Detector Type Suggested Skin Entrance Dose Ranges

(mGy)

D-speed Film 1.52 – 1.95a

E-F or F-speed Film 0.87 – 1.09a

Digital-PSP 0.52 – 1.04b

Digital- CMOS 0.44 – 0.87b

Digital- CCD 0.35 – 0.52b


98

Patient radiation doses for intraoral images receptors can vary widely based on several 2239

factors. Table 6.1 provides suggested exposure ranges for various detectors. It should be 2240

emphasized that the image quality and patient dose must be optimized with any detector and that 2241

the exposure ranges in Table 6.1 are merely a starting point. 2242

2243

6.3.1.4 Disadvantages and Challenges of Digital Imaging. In contrast to the advantages outlined 2244

above, digital imaging also has some disadvantages. 2245

2246

Presently, most digital image receptors tend to result in some discomfort for the patient. 2247

While patients will usually agree that no imaging device is comfortable, the flexibility of film 2248

packets compared to the rigid construction of most digital image receptors gives film the 2249

advantage with regard to patient comfort. Many sensors now come in a variety of sizes to 2250

accommodate different size patients. Digital image receptor manufacturers are addressing this 2251

issue with image receptors designed for improved patient comfort. Ergonomic ease is not limited 2252

to patient considerations. Some operators find the new digital imaging receptors challenging to 2253

handle during the x-ray examination (Annisi and Geibel, 2014). PSP digital systems offer 2254

flexible image receptors providing a level of patient comfort similar to film. These systems 2255

include a digital image processing stage prior to viewing the final radiograph. The clinical 2256

challenges of examining a patient with digital-based technology will likely improve in part as 2257

educational institutions better prepare dental students for these new technologies, and as 2258

technologies continue to evolve in response to these types of issues. Collectively, these should 2259

lead to a reduction in the number of repeat images. 2260

2261

Digital dental imaging equipment makes it difficult to see the relationship between x-ray 2262

exposure and overall image quality that is readily evident when using film. The relative broad 2263

exposure latitude provided by digital image receptors, especially PSP plates with their unique 2264

linear detector latitude (Farman and Farman, 2005), and the lack of feedback that film provided 2265

regarding over- and under-exposure can lead to patient exposures that are not optimized. Far 2266

from simple, “plug-n-play,” digital imaging systems require proper set-up at installation as well 2267

as continuous monitoring, much like conventional film-based systems. Failure to properly install 2268


99

and optimize these systems can lead to lower quality images and higher patient exposure, 2269

potentially higher than that required for D-speed film. 2270

2271

Recommendation 59. The dental practice should enlist the assistance from a qualified 2272

expert to ensure each new digital system is properly configured with regard to both 2273

patient dose and image quality. 2274

2275

The ease with which digital images can be captured and displayed, particularly for all to see, 2276

could motivate dental practices to acquire more images per patient than normally would be taken 2277

with film. Annisi and Geibel (2014), and Berkhout (2003) found that there was a slight but 2278

notable increase in the rate of images acquired per patient, particularly for CCD-based devices. 2279

This was mainly due to the receptor size and positioning of the image receptor. Therefore the 2280

dental practice should implement and adhere to imaging practices that minimize x-ray dose to 2281

patients to levels needed for the clinical task. 2282

2283

Regardless of the technology used to image patients, the dental practice should ensure the 2284

safe and secure storage of patient records including imaging exams. Unlike hardcopy film, 2285

digital images are merely data bits on a computer. Therefore a challenge to the digital-based 2286

dental office is to establish a routine practice for ensuring secure, long-term electronic storage of 2287

patient digital imaging data. This avoids unnecessary radiation resulting from duplicate 2288

examinations to replace images lost due to computer failure. Routine duplicate backup of patient 2289

images, stored off site, is a highly recommended practice to guard against unanticipated 2290

computer storage failure. Finally, the vulnerability of electronic records (medical or otherwise) to 2291

computer hacking mandates the implementation of secure equipment and records-keeping 2292

procedures to minimize this possibility. 2293

2294

In summary, the disadvantages of digital dental imaging include: 2295

2296

high initial cost; 2297

image receptor dimensions and rigidity can cause patient discomfort ; 2298

difficulty in maintaining infection control; 2299


100

maintaining secure electronic storage of patient records; 2300

ease of repeated images can motivate unnecessary retakes, resulting in increased patient 2301

radiation doses; and 2302

difficulty in identifying excessive doses, especially in the case of PSP, because 2303

unnecessarily high-dose images tend to be clinically acceptable. 2304

2305


2307

Digital imaging in dentistry requires specific equipment and facilities. These include the 2308

following major components: 2309

2310

image receptors (PSP or solid-state sensor); 2311

image processor for PSP; 2312

computer systems; 2313

image display monitors; and 2314

technique charts. 2315

2316

6.3.2.1 PSP Plates. The migration to digital imaging can eliminate certain routine costs such as 2317

the purchase of film and processing chemicals. However, PSP-based image receptors have a 2318

limited lifetime of useful performance and must be periodically replaced. A limited study by 2319

Ergün et al. (2009) on a sample of PSP image receptors showed that the devices can provide 2320

clinically acceptable images over a lifetime of up to 200 exposures. However, the useful life 2321

depends on the appropriate handling of the PSP plates. Figure 6.2 shows and example of a good 2322

quality image, while Figure 6.3 shows some examples of plates that should be replaced as soon 2323

as possible. The cost of replacing PSP plates is in the range of $25 to $30 per plate. However, 2324

producing a quality image should be the priority over the cost of replacement plates. 2325


101

2326

2327

2328

2329

2330

2331

2332

2333

2334

Fig. 6.2. Example of good quality image of test phantom. This phantom consists of a Luxel 2335

dosimeter with an extra filter added. It is placed ~5 cm above the film or digital detector. 2336

2337


102

2338

2339

2340

2341

2342

2343

2344

2345

2346

2347

2348

2349

2350

Fig. 6.3. Examples of damaged PSP plates. (Top left) Scratches and frayed edges; (top right) 2351

Scratches or cracked phosphor; (bottom left) Scratches, stains, and low contrast; (bottom right) 2352

Stains of phosphor plate (coffee, soda?). 2353

2354

2355


103

Photostimulable storage phosphor (PSP) image receptors function similar to conventional 2356

computed radiography (CR) devices in medicine. The receptor consists of a thin imaging plate 2357

encapsulated in a protective, light-proof cover. The receptor is pliable, and, therefore, provides 2358

the patient with a similar experience as with traditional film. Once the x-ray exposure is made, 2359

the plate is read. In this reading process the plate is scanned with a laser and light is emitted in 2360

proportion to the x-ray exposure of the receptor surface, with the amount of light being converted 2361

into pixel intensity values. This image is then stored as a digital image and presented on a 2362

computer display. Unlike direct digital-based technologies where the image is available near-2363

instantly, PSP-based imaging requires a scanning stage before the image can be viewed. 2364

2365

Early PSP devices were capable of spatial resolution of ~6 c mm–1, compared to ~20 c mm–1 2366

for film when exposed and processed properly. One study also found that the latent image on the 2367

PSP plate will degrade if the plate is not processed soon after the exam. Newer PSP-based 2368

systems are capable of resolutions of ~11 c mm–1 or better. Interestingly, even early PSP devices 2369

were shown to have better low-contrast performance than film (Figure 6.4) and to have better 2370

exposure latitude than CMOS based systems (Farman and Farman, 2005) and film (White and 2371

Pharoah, 2014). 2372

2373

There are a number of benefits to PSP-based imaging for dental applications, particularly for 2374

intraoral imaging. The PSP plates are very similar in size and flexibility to film packets and do 2375

not require wires, providing patients an experience similar to film. Although a PSP image reader 2376

is required, the image plates are much less costly to replace than the direct digital image 2377

receptors, and the need for chemicals and film handling facilities (e.g., darkroom) are eliminated, 2378

although a PSP plate scanner and a low light level room are needed for handling the PSP plates. 2379

Sizes of PSP plates available for routine imaging include Size 0 (~35 ・ 22 mm) up to Size 4 2380

(~76 ・ 57 mm). Sizes suitable for cephalometric, panoramic, and temporomandibular joint 2381

(TMJ) imaging are also available. 2382

2383


104

2384

2385

2386

2387

2388

2389

2390

Fig. 6.4. Images of a test phantom showing differences in contrast between a digital image 2391

(left) and film image (right). Smaller inset darker gray area in circle (upper right) is a low 2392

contrast area which is visible in the digital image but not visible in the film image. Likewise, 2393

light gray linear structures are visible on the left and barely visible on the right. 2394

2395

2396


105

6.3.2.2 Solid State Receptors. Unlike PSP-based imaging technology where the latent image is 2397

digitized during the storage plate readout process, the direct digital image receptors for dental 2398

radiography are digitized immediately after exposure within the image receptor, and images are 2399

available almost immediately after the exposure is made. The active receptor layer in direct 2400

digital image receptors are CMOS-based (complementary metal oxide semi-conductor) or CCD-2401

based (charge-coupled device). Early receptor devices provided only a wired connection for data 2402

transfer to a computer for processing and eventual display. Newer systems are now capable of 2403

wireless transmission of image data. Direct digital image receptors are rigid; therefore patients 2404

may not tolerate them as readily as they might with conventional film packets or PSP image 2405

receptors. Aside from some potential patient discomfort, a benefit from direct digital imaging is 2406

the near-instant availability of clinical images. Similar to PSP-based systems, direct digital-based 2407

image capture provides all the benefits of electronic image processing and display, archiving, 2408

and communications of images. 2409

2410

There are a number of benefits to CCD- and CMOS-based imaging for dental applications. In 2411

comparison to film, solid state digital receptors have a much wider dynamic range and are 2412

partially decoupled from the characteristics of the entering x-ray beam. Software applications 2413

allow manipulation of the displayed image to rescue nondiagnostic raw images, thus avoiding re-2414

exposure of the patient. An underexposed receptor image can be manipulated to improve contrast 2415

and density; however, such manipulation will lose fine detail. Conversely, an overexposed 2416

receptor image will yield useful information with post-processing, at the expense of 2417

unnecessarily overexposing the patient (in this case, post-processing is comparable to the 2418

overexposure and underdevelopment of film). 2419

2420

Solid state detectors are subject to damage and other issues associated with electronic 2421

imaging. Some examples detectors that should be replaced are shown in Figure 6.5. 2422

2423

2424


106

2425

2426

2427

2428

2429

2430

2431

2432

2433

2434

2435

Fig. 6.5. Examples of solid state detectors with problems degrading image quality. (Top left) 2436

honey-combed background can be eliminated by appropriate subtraction of flat-field image. This 2437

detector also shows a chip on left, a line across the detector, and a light, cone-shaped area. (Top 2438

right) residual latent image from a high density object (step wedge) due to failure to erase or 2439

clear the sensor image before acquiring the next image. (Bottom left) background pattern of 2440

unknown origin. (Bottom right) pattern caused by short in the cord connecting the detector to the 2441

computer (courtesy of W.D. McDavid and J.E. Gray). 2442

2443


107

2444

6.3.2.3 Converting from Film to Digital Imaging—Potential Dose Reduction. Digital radiography 2445

offers advantages to the dentist and ancillary staff. The image is available almost instantly; there 2446

is no need for a darkroom or film processing; images can be stored and retrieved digitally; and 2447

radiation dose reductions on the order of 40 to 70 %, or more, are possible compared to film 2448

radiography (Table 6.1). However, the ease and speed of acquisition and viewing can lead to 2449

unnecessary re-exposures. In addition, post-processing image manipulation can lead to 2450

inappropriate radiation doses to patients and less than ideal, or even nondiagnostic, images; this 2451

is especially true with PSP plates where inadvertent overexposure is easily done. These two 2452

practice behaviors can lead to systematic overexposures to the patients. 2453

2454

Recommendation 60. When converting from film to digital imaging, the facility shall 2455

make proper exposure technique (time) adjustments, commensurate with the digital 2456

imaging system. 2457

2458

6.3.2.4 Technique Charts. Another method to ensure image quality, while reducing operator 2459

exposure and providing for patient dose optimization is the utilization of size-based technique 2460

charts or protocols. Technique charts should be unique to each x-ray unit and image receptor 2461

combination displaying suggested technique settings for a specific anatomical area along with 2462

the patient size (small, medium, large) for adults and children. These should be developed for 2463

both intraoral and extraoral imaging, listing the exam, patient size, along with adult and pediatric 2464

settings, and image receptor (film type, digital image receptor). Technique charts should be 2465

posted near the control panel where the technique is adjusted for each x-ray unit. With digital 2466

workstations, technique charts may also be readily placed on the workstation’s desktop. When 2467

the x-ray unit is replaced, or an image receptor is added, the chart must be updated. An example 2468

of a technique chart is shown in Figure 6.6. 2469

2470

6.3.2.5 Clinical Image Display Monitors for Digital Imaging. An imaging display is a very 2471

important component in digital radiology. Most image display monitors are liquid crystal 2472

displays (LCD); newer LCD displays have light emitting diode (LED) backlights. Organic light 2473


108

Sample Technique Chart 2474

Brand X Unit, Room 2 2475

Brand Y Digital Image Receptor, Size 2 2476

70 kVp, 7 mA 2477

Exposure Time, sec

Child Adult

(standard)

Adult

(large)

Maxillary

Incisor or Canine 0.05 0.07 0.09

Premolar 0.06 0.09 0.12

Molar 0.07 0.11 0.14

Mandibular

Incisor or Canine 0.04 0.06 0.08

Premolar 0.04 0.06 0.08

Molar 0.05 0.07 0.09

Bitewing

Anterior 0.04 0.06 0.08

Posterior 0.07 0.07 0.09

Occlusal

0.08 0.12 0.16

2478

Fig. 6.6. Sample technique chart indicating the x-ray unit, image receptor, kilovoltage, 2479

milliampere, and exposure time for various projections for adult patients of two sizes and for a 2480

pediatric patient. 2481

2482

2483


109

emitting diode (OLED) displays may soon be commercially available.. Image displays may be 2484

monochrome or color. 2485

2486

The amount of ambient light in an interpretation room has a significant impact on image 2487

interpretation; the ambient light levels must be controlled and only indirect lighting allowed. 2488

2489

Medical grade image displays have several advantages over off-the-shelf display monitors, 2490

including the capability of adjusting the brightness to compensate for variations in the intensity 2491

of the back light and ambient room light. If commercial off the shelf displays are used, it is 2492

important that periodic calibration be performed to maintain optimal performance (Section 2493

5.2.6). A poor display quality may lead to inaccurate diagnosis and may result in inappropriate 2494

treatment for a patient. 2495

2496


110

7. Intraoral Dental Imaging 2497

2498

7.1 General Considerations 2499

2500

7.1.1 Beam Energy 2501

2502

Intraoral dental x-ray machines have been marketed with peak x-ray tube operating 2503

potentials ranging from 40 to >100 kVp. Units operating below 60 kVp result in higher than 2504

necessary radiation doses to the patient (AAPM, 2015). 2505

2506

The operating potentials for intra-oral imaging equipment should be lower than for other 2507

dental imaging because the goal is to deposit x-ray photons into an imaging receptor just behind 2508

the teeth instead of an image receptor on the opposite side of the patient’s head. Published data 2509

show no relationship between peak operating potential and effective dose to the patient with 2510

beam energies ranging from 70 to 90 kVp (Gibbs et al., 1988a). These data apply specifically to 2511

half-wave rectified intraoral dental x-ray machines. Similar beam energy spectra are produced by 2512

modern constant-potential machines operating up to 10 kV below the kilovoltage of full-wave or 2513

half-wave rectified machines. There is little to be gained from operating potentials higher than 2514

80 kVp. In fact, higher kilovoltages decrease the inherent contrast in the images and are, 2515

therefore, detrimental to diagnostic image quality. Most contemporary intraoral x-ray units 2516

operate at a fixed operating potential in the 60 to 70 kV range. 2517

2518

Recommendation 61. The operating potentials of intraoral dental x-ray units shall not 2519

be <60 kVp and should not be >80 kVp. 2520

2521

7.1.2 Position-Indicating Devices 2522

2523

A position-indicating device (PID) provides a visual aid to the operator in aligning the x-ray 2524

beam properly to the structure(s) being imaged. Position-indicating devices are attached to the x-2525

ray tube head, are open-ended, and may be combined with higher atomic number materials that 2526

absorb scattered radiation arising from the patient, collimator, and filter. 2527


111

2528

Recommendation 62. Position-indicating devices shall be open-ended devices and 2529

should provide attenuation of scattered radiation arising from the patient, collimator or 2530

filter. 2531

2532

The length of the position-indicating device determines the source-to-skin distance. Short 2533

source-to-skin distances (or source-to-image receptor distances) produce unfavorable dose 2534

distributions (van Aken and van der Linden, 1966; White and Pharoah, 2014). They will degrade 2535

the sharpness of the images, and also produce excessive magnification or distortion of the image, 2536

sometimes limiting anatomic coverage. 2537

2538

Recommendation 63. Source-to-skin distance for intraoral radiography shall be at least 2539

20 cm and preferably should be at least 30 cm. 2540

2541

7.1.3 Rectangular Collimation 2542

2543

All medical and dental diagnostic x-ray procedures, except intraoral radiography, must be 2544

performed with the beam collimated to the area of clinical interest; in no case can it be larger 2545

than the image receptor (FDA, 2015). Positive beam-receptor alignment is required to ensure that 2546

all exposed tissue is recorded on the image. However, requirements and recommendations to 2547

date have permitted circular beams for intraoral radiography whose area, measured in the plane 2548

of the receptor, may be up to three times the area of a size 2 receptor, and four to five times the 2549

area of a size 0 receptor. Rectangular collimation of the beam to the size of the image receptor 2550

reduces the tissue volume exposed, especially that of the more sensitive parotid and thyroid 2551

gland tissues. This would reduce the effective dose to the patient by a factor of four to five, while 2552

simultaneously improving image contrast and overall diagnostic quality by reducing the amount 2553

of scattered radiation (Cederberg et al., 1997; Dauer et al., 2014; Freeman and Brand, 1994; 2554

Gibbs, 2000; Gibbs et al., 1988; Underhill et al., 1988; White and Pharoah, 2014). 2555

2556

Due to the close tolerances between the x-ray beam and receptor sizes, it may be necessary to 2557

use a positioning device to assure complete coverage of the image receptor by the x-ray beam. A 2558


112

variety of types, known as positioning devices, paralleling devices, or film or image receptor 2559

holders, are available. Rectangular collimation is recommended by the American Dental 2560

Association, the Food and Drug Administration, and the National Council on Radiation 2561

Protection and Measurement (FDA/ADA, 2015a; 2015b; NCRP, 2004). 2562

2563

Rectangular collimators may be attached either to the position-indicating device or may be a 2564

part of the receptor-holding device. Receptor-holding devices are used to both stabilize intraoral 2565

image receptors in the mouth, and help align the position-indicating device on the x-ray tube 2566

head. Receptor-holding devices thus reduce artifacts from motion, misalignment, or other 2567

distortions while making radiographs. Receptor-holding devices should be used whenever 2568

possible. 2569

2570

It should be noted that ~50 % of the dental facilities in Great Britain use rectangular 2571

collimation (Holroyd, 2013).2 Most academic institutions in the United States teach this 2572

technique but the proportion of dentists using rectangular collimation is much lower than in 2573

Great Britain, i.e., on the order of only 15 % (Farris and Spelic, 2015). 2574

2575

Anatomy or the inability of occasional specific patients to cooperate, including some 2576

children, may make rectangular collimation and beam-receptor alignment awkward or 2577

impossible for some projections. The rectangular collimation requirement may be relaxed in 2578

these rare cases. 2579

2580

The amount of the patient’s anatomy exposed to radiation with circular collimation is shown 2581

in Figures 7.1, 7.2, and 7.3. Figure 7.2 also shows that a significant amount of radiation exits the 2582

patient’s head on the side opposite the x-ray tube. It should be noted that not all rectangular 2583

collimators produce the same size x-ray field at the skin surface. Collimators which attach to the 2584

end of existing round position indicating devices will provide smaller fields with longer position 2585

indicating device length. Some commercial rectangular collimators produce inherently larger 2586

2587

2 Gray, J.E. (2015). Personal communication (DIQUAD, LLC, Steger, Illinois)


113

2588

2589

2590

Fig. 7.1. (a) This image shows the entry and exit exposed tissue volumes with round 2591

collimation (above) versus rectangular collimation (below). (b) The area of the primary beam 2592

exiting the round PID is three times greater than the area of a typical size 2 dental film. Thus, 2593

two-thirds of the primary beam without rectangular collimation is not used to create an image 2594

and is an unnecessary radiation exposure to the patient. Thus, the exposed volume is significantly 2595

reduced when rectangular collimation is used (adapted from White and Pharoah, 2014.) 2596

2597

a. b.


114

2598

2599

2600

2601

2602

2603

2604

2605

2606

2607

Fig. 7.2. This image was created by holding a rare-earth screen-film cassette at the exit side 2608

of a patient’s head. The film packet contained a lead foil and one Size 2 intraoral film, shown at 2609

the left. It is clear that the film packet absorbs only a small portion of the x-ray beam and that a 2610

large volume of the patient is exposed to radiation when a rectangular collimator is not used. 2611

This also provides an indication of the unnecessary amount of radiation exiting the patient on the 2612

side opposite the x-ray tube (images courtesy of J.E. Gray) 2613

2614


115

2615

2616

2617

2618

2619

2620

2621

2622

2623

Fig. 7.3. Radiation fields at entry using round collimation versus rectangular collimation 2624

superimposed over a line drawing of a panoramic image. The exposed tissue area and resulting 2625

scatter are significantly reduced when rectangular collimation is used. 2626

2627


116

radiation fields leading to less dose reduction in comparison with alternative rectangular 2628

collimators (Johnson et al. 2014). 2629

2630

Recommendation 64. Rectangular collimation of the x-ray beam shall be used routinely 2631

for periapical and bitewing radiography, and should be used for occlusal radiography 2632

when imaging children with size 2 receptors. 2633

2634

7.1.4 Patient Restraint 2635

2636

It may be necessary, in a limited number of cases, that uncooperative patients be restrained 2637

during exposure or that the image receptor be held in place by hand. A member of the patient’s 2638

family (or other caregiver) should provide this restraint or receptor retention. 2639

2640

Recommendation 65. Occupationally-exposed personnel should not routinely restrain 2641

uncooperative patients and shall not hold the image receptor in place during an x-ray 2642

exposure. 2643

2644

Recommendation 66. Comforters and caregivers who restrain patients or hold image 2645

receptors during exposure shall be provided with shielding, e.g., radiation protective 2646

aprons, and should hold the film holding device. No unshielded body part of the person 2647

restraining the patient shall be in the primary beam. 2648

2649

7.1.5 Diagnostic Reference Levels and Achievable Doses 2650

2651

For intraoral radiography, most published DRLs and ADs are based upon entrance air kerma 2652

(Hart et al. 2012; NCRP, 2012b). NCRP Report No. 172 (NCRP, 2012b) recommends for 2653

intraoral bitewing and periapical radiography a DRL of 1.6 mGy entrance air kerma, which was 2654

the 75th percentile value for E-speed film in the 1999 NEXT dental survey (NCRP, 2012). NCRP 2655

Report No. 172 also recommends an AD of 1.2 mGy; this was the median dose for E-F film in a 2656

State of Michigan survey (LARA, 2015). NCRP Report No. 172 notes, “It is recognized, and 2657

intended, that meeting this standard will most likely require dentists in the United States who use 2658


117

D-speed film to convert to E-F- or F-speed film.” Most digital image receptors should produce 2659

adequate images at entrance air kermas well below these DRLs and Ads, as shown by Table 6.1. 2660

2661

7.1.6 Best Practices 2662

2663

Best practices in intraoral imaging are easily and inexpensively attained with commercially 2664

available equipment with three simple steps: 2665

2666

1. using E-F- or F-speed films reduces the effective dose per image by 50 % or more 2667

compared to D-speed film; 2668

2. using digital image receptors reduces the effective dose per image by 50 to 75 % 2669

compared to D-speed film; 2670

3. using rectangular collimation reduces the effective dose per image by a factor of three to 2671

five, depending on receptor size, compared to round collimation. 2672

2673

Table 7.1 shows the potential for dose reductions by modifying receptor speed and collimation 2674

type. It is clear that simple changes can reduce patient effective dose by as much as 90 %, i.e., 2675

the patient is receiving only 10 % of the effective dose compared to the original technique! 2676

2677

In addition to the significant dose reductions from the use of the fastest receptors and 2678

rectangular collimation, thyroid shielding provides additional protection, especially in children, 2679

where the thyroid is more sensitive to radiation carcinogenesis and is higher in the neck. 2680

2681

7.1.7 FDA Clearance of Dental Imaging Equipment 2682

2683

X-ray units and digital imaging systems used in dental radiography must be cleared by FDA. 2684

The Internet allows purchasing such equipment from suppliers outside of the United States who 2685

may be providing items that have not been cleared by the FDA (Section 10.1). 2686

2687


118

TABLE 7.1—Effective doses for intraoral dental radiographic views.a 2688

Technique Effective Dose (µSv)

FMXb with D-speed film and round collimation 388

FMX with PSP or F-speed film and round collimation 171

FMX with CCD and round collimation (estimated)c 85

FMX with PSP or F-speed film and rectangular collimation 35

FMX with CCD and rectangular collimation (estimated)c 17

Two BWs with PSP or F-speed film and rectangular collimation 5

2689

a Adapted from Ludlow and Ivanovic (2008). 2690

bFMX = full mouth series = consists of 16 to 20 individual intraoral images 2691

c White and Pharoah (2014). 2692

2693


119

7.2 Conventional X-Ray Systems (Wall Mounted and Portable) 2694

2695


2697

Intraoral dental x-ray sources are available in three different configurations. The x-ray source 2698

may be attached to an immovable fixture to the wall or ceiling of the operatory, a mobile unit 2699

supported by a mechanical stand on wheels, or a hand-held device not supported by any 2700

mechanical fixture (Section 7.3). Conventional wall- or ceiling-mounted dental x-ray sources are 2701

the most common type of dental x-ray units. 2702

2703


2705

The wall- or ceiling-mounted x-ray units should have the following components: a control 2706

timer unit mounted to the wall or connected by a retractable coiled cord and an articulating arm 2707

that connects the x-ray tube to the wall or ceiling fixture. The control unit provides options to 2708

select kilovoltage and milliamperage (if these are not fixed), and exposure time. 2709

2710

The control unit shall provide a visual and audible signal during the emission of x radiation. 2711

The x-ray exposure shall be controlled by a dead man’s switch, i.e., the exposure must be 2712

terminated immediately on release of the switch. If the control unit is for a wall or ceiling 2713

mounted x-ray tube, the switch should be positioned behind a barrier so that the operator must 2714

stay behind the barrier during the exposure, i.e., the exposure switch must be at least 1 m from 2715

any outside edge of the barrier. If the system is a mobile x-ray unit, the control unit must be 2716

connected with a retractable cord and the working length of the cord shall be at least 2 m. 2717

2718

Although a wall- or ceiling-mounted unit is preferred, there may be circumstances where 2719

a mobile x-ray unit may be used. The advantage of such units are use in dental operatories that 2720

do not have x-ray units, operating and emergency rooms, or in temporary clinical facilities. A 2721

mobile unit shall have the same safety features as a wall- or ceiling-mounted unit. 2722

2723


120

Recommendation 67. The stand of a mobile unit shall provide adequate support to the 2724

x-ray tube during travel and when the articulating arm is fully extended, and during x-2725

ray exposure. The wheels or the casters shall be equipped with a foot brake to prevent 2726

motion of the unit during exposure. 2727

2728

There are circumstances, such as intra-procedure imaging in an operating room or images 2729

acquired on children who have to be seated in their parent’s lap where it is not reasonable to have 2730

all persons cleared from the area during x-ray exposures. In such instances, the distance 2731

recommendations concerning positioning of the operator should be observed. 2732

2733

Recommendation 68. Only the patient and operator shall be in the area during an 2734

exposure unless special circumstances do not allow this. 2735

2736

7.2.2.1 Protection of the Operator and Shielding. Guidance for protection of the operator and 2737

shielding are in Section 4.5 and Appendix D. 2738

2739

7.2.2.2 Tube Head Positional Stability. The articulated arm that supports the x-ray tube head 2740

must be capable of achieving any position and angulation required for intraoral radiography, and 2741

maintaining it until the exposure is complete. 2742

2743

Recommendation 69. The tube head shall achieve a stable position, free of drift and 2744

oscillation, within 1 s after its release at the desired operating position. Drift during that 2745

1 s shall be no greater than 0.5 cm. 2746

2747

7.2.2.3 Position-indicating Devices. The description and recommendations governing 2748

collimation and tube length of position-indicating devices are covered in Section 7.1.2. 2749

2750

7.2.2.4 Rectangular Collimation. The description and recommendations governing rectangular 2751

collimation are covered in Section 7.1.3. 2752


121

2753

7.3 Hand-Held X-Ray Systems 2754

2755


2757

Recent developments in x-ray sources for intra-oral dentistry have included systems that are 2758

designed to be held by the operator during use. 2759

2760

Optimal use of hand-held dental x-ray sources in intra-oral imaging requires adherence of 2761

equipment to certain design principles beyond those of wall-mounted systems. Traditional 2762

methods of shielding, including the utilization of fixed barriers and maximizing the source to 2763

operator distance, are not applicable to sources that are designed to be handheld. Indeed, the 2764

requirement that the operator never hold the x-ray source does not apply to devices that are 2765

designed to be hand-held. In these cases, due to the proximity of the operator to the x-ray source, 2766

increased radiation risks require additional design considerations. While the recommendations 2767

below are specific to hand-held equipment, other applicable design considerations such as 2768

Federal performance standards, and international standards (IEC, 2012) must still be observed. In 2769

particular, leakage radiation and backscatter radiation potentially pose a greater risk to the 2770

operator when using a hand-held x-ray source because the operator must be near the device for 2771

operation. In order to mitigate these risks, additional shielding is incorporated into the design. 2772

2773

The first contemporary hand-held dental x-ray units were introduced in 2005 and today there 2774

are over 17,500 in use in the United States (with a growth rate of 15 % y–1). Initially the sale of 2775

these units met resistance from the regulatory community due to an old rule of thumb, sometimes 2776

in regulations and other times not, that one should never hold the x-ray tube. This is a valid rule 2777

for conventional x-ray tubes due to leakage radiation from the tubes. However, properly 2778

designed hand-held dental x-ray units are specially shielded to minimize the dose to the hands 2779

and body of the operator (Gray et al., 2012). Many papers have been published by different 2780

investigators demonstrating the safety and effectiveness of a properly shielded hand-held dental 2781

x-ray unit (Danforth, 2009; Goren, 2008; Gray et al., 2012). 2782

2783


122

Figure 7.5 (left) shows a hand-held dental x-ray unit, cleared by FDA for sale in the 2784

United States, that has a leaded-acrylic x-ray shield affixed to the front. This shield protects the 2785

operator’s hands and body from backscattered radiation when properly oriented. Figure 7.5 2786

(right) shows the operator using this hand-held unit to make an intraoral dental radiograph. The 2787

zone that is protected by the leaded acrylic shield can be clearly seen (the green area as opposed 2788

to the red area). 2789

2790

7.3.1.1 Advantages of Hand-Held X-Ray Units. Hand-held units can often be used in 2791

environments or circumstances where use of fixed or mobile units is either extremely 2792

cumbersome or impossible, such as operating rooms, emergency rooms, nursing homes, and 2793

remote locations, and intraoperative endodontic and pediatric dental imaging. In addition, they 2794

are quite useful in forensic investigations and in the identification of remains during a major 2795

catastrophe. The following lists some of the other features and advantages: 2796

2797

They are especially helpful in patients with special needs and in surgical operatories 2798

where traditional x-ray machines cannot be easily used during certain procedures. 2799

Hand-held x-ray units provide low radiation exposure to the operator if appropriate 2800

operating instructions are followed. The radiation dose is comparable to wall-mounted x-2801

ray machines. 2802

They are capable of producing sharp images even with mild operator movement. 2803

They are easy to operate and position. 2804

The quality of the radiographs made from hand-held devices is comparable to traditional 2805

wall-mounted devices. 2806

One hand-held unit can be shared between two or more rooms. 2807

2808

7.3.1.2 Disadvantages of Hand-Held X-ray Units. There are disadvantages to hand-held x-ray 2809

units. Some states may impose restrictions on their use. Some can be operated without a 2810

backscatter shield (none is provided or it can be removed), which increases the radiation dose to 2811

the operator. Other potential disadvantages include: 2812

2813


123

2814

2815

2816

2817

2818

2819

2820

2821

2822

2823

2824

Fig. 7.5. A hand-held unit cleared by FDA for sale in the United States. (Left) unit showing 2825

leaded-acrylic shield on front. (Right) leaded-acrylic shield provides protected zone (in green) 2826

for the user compared to no protection (red-to-pink). In an actual patient image acquisition, 2827

rectangular collimation would be used. In order to best illustrate the effect of the acrylic 2828

shielding, rectangular collimation was not included in this illustration. 2829

2830


124

2831

Misalignment between the unit and the film or receptor, especially if a beam-guiding 2832

device is not used. 2833

The operator must put down the hand-held unit down while positioning film or image 2834

receptor in the patient’s mouth, thus increasing the risk of cross-contamination. 2835

Some are more expensive than traditional x-ray units. 2836

If used incorrectly there can be increased dose to the operator. 2837

Some are heavy and can be awkward and inconvenient to use; using such a machine for a 2838

long time can cause operator fatigue. 2839

Some of the units require connection to a power source which limits their mobility. 2840

While the batteries in the units are capable of powering multiple exposures, they require 2841

an electrical source for recharging and it is possible that there might not be sufficient 2842

power for multiple exposures from a single charge, especially in remote sites. 2843

Infection control is often difficult, especially when a plastic bag is used as the barrier. 2844

Some of the units, especially those available on the Internet, are not cleared by the FDA 2845

for sale in the United States; however, such units are available in the market for purchase 2846

at very low, attractive prices. Such units may exhibit the following problems: 2847

o high leakage radiation; 2848

o no “dead-man switch”; 2849

o actual (measured) kV is far below the indicated value; 2850

o no audible signal of x-ray exposure; 2851

o poor quality components more likely to break down quickly; and 2852

o low image quality due to low x-ray output and resultant long exposure times to 2853

acquire a diagnostic image. 2854

2855

Individuals responsible for the purchase of hand-held x-ray units must be certain that the unit has 2856

been cleared by the FDA. This will be indicated by the label on the device, illustrated in 2857

Figure 10.1. 2858

2859

7.3.1.3 Safety Issues with Improper Handling of Hand-Held X-Ray Equipment. The design of 2860

hand-held x-ray equipment presents different challenges for protecting patients, operators, and 2861


125

the public from unnecessary radiation exposure. In particular, device positioning, weight, and 2862

security and access controls introduce additional radiation safety issues that must be considered 2863

when using hand-held x-ray equipment. 2864

2865

Many of the assumptions about positioning that are made for wall-mounted systems are not 2866

valid when using a hand-held x-ray system. While permanent installation for a wall-mounted 2867

system allows assumptions to be made about minimum distances between the x-ray equipment 2868

and members of the public, and permanent shielding to be placed between the source and other 2869

patients, these are not always true for hand-held systems. 2870

2871

There is no control for the distance between the source and members of the public for hand-2872

held x-ray systems. The operator must ensure that there is proper distance and shielding between 2873

the source and members of the public. When used in a dental facility to replace a wall-mounted 2874

system, using the hand-held system in the same location as a conventional x-ray machine will 2875

provide sufficient radiation protection for members of the public. More information is needed to 2876

develop guidelines for equipment used outside of the dental office where there is most likely 2877

inadequate shielding design. 2878

2879

The hand-held nature and weight of these systems also introduces risks due to operator 2880

fatigue from holding the device for multiple imaging exams. Operator fatigue can lead to poor 2881

positioning of the system, which can lead to poor quality radiographs and the need for repeated 2882

exposures. Additionally, fatigue could cause the operator to hold the device closer to the chest, 2883

possibly moving the backscatter shield sufficiently back to expose parts of the operators head. 2884

Thus, operators of hand-held x-ray equipment must have the physical ability to hold the system 2885

in place for all exams. This should be taken into consideration while evaluating operator 2886

workloads to minimize the need for repeat exposures to patients. 2887

2888

Recommendation 70. Operators of hand-held x-ray equipment shall have the physical 2889

ability to hold the system in place for multiple exposures. 2890

2891


126

Additional training is necessary for all operators of hand-held x-ray equipment to introduce 2892

them to the proper operation of these units. This training should include topics such as proper 2893

positioning with the hand-held unit, variations in positioning which improve radiation safety of 2894

staff, and safe areas relative to the leaded-acrylic shield and the necessity for its use. 2895

2896

Recommendation 71. Manufacturers should provide a training program for users of 2897

hand-held equipment to emphasize the appropriate safety and positioning aspects of 2898

their unit. 2899

2900

Many hand-held systems are designed such that the exposure button can be found intuitively 2901

by nontrained users. This benefits operators and reduces the amount of training necessary, but 2902

also increases the risk of use by a nonqualified operator, and even children. Operators and 2903

manufacturers can both take steps to mitigate this risk. 2904

2905

Methods to prevent the unauthorized use of hand-held x-ray units should be implemented, 2906

e.g., a key lock, or a software key that the operator would be required to enter before the device 2907

could be activated. In addition, an exposure counter would provide information about the total 2908

number of exposures and, along with an exposure log, would allow the practitioner to monitor 2909

the use of the equipment. 2910

2911

Recommendation 72. Operators shall store hand-held x-ray equipment such that it is 2912

not accessible to members of the public when not in use. 2913

2914

Recommendation 73. Manufacturers of hand-held x-ray equipment shall incorporate 2915

either hardware or software interlocks on their devices to prevent unauthorized use. 2916

Hardware interlocks may include physical keys or locks necessary for operation while 2917

software interlocks may include password restrictions. 2918

2919

7.3.1.4 Exception to “Never Hold the X-Ray Unit.” Traditional radiation protection 2920

recommendations instruct users to never hold the x-ray unit. The rationale behind this 2921

recommendation is that leakage radiation from the x-ray unit and backscatter radiation expose 2922


127

the operator to unnecessary radiation. This recommendation is both unnecessary and impractical 2923

for properly designed hand-held x-ray systems that have been FDA-cleared. Properly designed 2924

hand-held x-ray systems include sufficient shielding around the x-ray unit, and backscatter 2925

shielding to protect the operator and mitigate the traditional risks associated with holding the x-2926

ray unit. Properly designed equipment should also include identification of the areas in which it 2927

is safe for the operator to stand during exposures based on the specific protective shielding in the 2928

device design. 2929

2930

Hand-held systems that are not properly designed and not FDA-cleared present the same or 2931

greater risks as traditional x-ray systems and should not be used. More information can be found 2932

in Section 10.1.1 to determine if a particular unit is properly designed and labeled. 2933

2934

Recommendation 74. Instructions supplied with hand-held x-ray equipment shall 2935

include identification of the areas in which it is safe for the operator to stand during 2936

exposures based on the specific protective shielding in the device design. 2937

2938

7.3.2 Equipment 2939

2940

Hand-held x-ray units must include safety interlocks to prevent unauthorized exposures, a 2941

clear shield on the end of the PID to protect the operator from scattered radiation, and additional 2942

shielding to reduce the leakage radiation to the operator. Some states are promulgating specific 2943

hand-held dental radiography regulations; dentists, operators and qualified experts must know 2944

the current regulations in their localities. 2945

2946

7.3.2.1 Backscatter Shield. Since the operator is standing near the patient there is a potential for 2947

increased exposure from back-scattered radiation. 2948

2949

Recommendation 75. Hand-held x-ray devices shall include a clear, external, 2950

nonremovable, radiation protection shield containing a minimum of 0.25 mm lead 2951

equivalence between the operator and the patient to protect the operator from 2952

backscatter radiation. 2953


128

2954

7.3.2.2 Leakage Radiation. Some hand-held dental x-ray units fail to meet FDA standards. In 2955

February 2012, the FDA issued a Safety Communication regarding units made overseas and 2956

being sold on the Internet without FDA clearance (FDA, 2012). In June 2012, the Health 2957

Protection Agency (HPA) of the United Kingdom issued an alert regarding similar equipment 2958

and published a report of their measurements (HPA, 2012). This device was neither cleared by 2959

the FDA (Figure 10.1) nor does it carry a CE mark. In December, 2014, a similar report was 2960

published in the United States concerning yet another similar system (Mahdian et al., 2014). 2961

2962

The HPA report indicates that the unit they evaluated (Figure 7.6) had several problems 2963

including: 2964

2965

1. substantial radiation leakage from the x-ray source in the front of and behind the unit 2966

(Figure 7.7a and 7.7b); 2967

2. no shielding is provided to protect the operator from backscattered radiation (Figure 7.6); 2968

3. the operator’s hands receive a dose of 7.5 mGy for each x-ray exposure; 2969

4. exposure times were long, e.g., 3 s, which could result in motion and blurred images; and 2970

5. operator annual dose for 100 x-ray exposures per week was estimated at 40 Sv equivalent 2971

dose to the hands and 30 mSv effective dose to the body. 2972

2973

7.3.2.3 Radiation Protective Equipment and Personal Radiation. Hand-held systems with 2974

internal and backscatter shielding have been shown (Danforth, 2009; Goren, 2008; Gray et al., 2975

2012) to be effective in protecting the operator from radiation exposure. Operator exposure when 2976

using these hand-held systems according to the manufacturer’s instructions is generally 2977

comparable to the operator exposure associated with wall mounted systems. Due to the 2978

effectiveness of internal and backscatter shielding of properly designed equipment, personal 2979

protective shielding is not necessary for the operator of hand-held x-ray units. 2980

2981


129

2982

2983

2984

2985

2986

2987

2988

2989

2990

Fig. 7.6. Example of hand-held dental x-ray system, not cleared by FDA. This device, 2991

manufactured outside the United States, does not carry a CE mark and has not been cleared by 2992

the FDA. It is marketed under several names. (This device was sold in the United States even 2993

though it was not FDA cleared.) 2994

2995


130

2996

2997

2998

2999

3000

3001

3002

3003

3004

3005

3006

Fig. 7.7. (a) Radiographic image showing the radiation from the front of a non-FDA cleared 3007

hand-held x-ray unit. In addition to the primary beam there is a substantial amount of leakage 3008

radiation also exposing the patient. (b) Radiographic image showing the radiation leaking from 3009

the back of this hand-held x-ray unit which would expose the user to unnecessary radiation 3010

(courtesy of the Health Protection Agency of the United Kingdom). 3011

3012

Primary

Leakage

a b


131

3013

Recommendation 76. The operator of a hand-held x-ray unit shall not be required to 3014

wear a personal radiation protective garment. 3015

3016

Likewise, there is no need for personal radiation monitoring with hand-held x-ray equipment 3017

as long as the whole-body effective dose to the operator is below 1.0 mSv y-1. It is prudent for 3018

operators to use personal monitors when initially using hand-held x-ray units (e.g., for six 3019

months) to confirm their radiation exposure levels. 3020

3021

7.3.2.4 Appropriate Use of Hand-Held X-Ray Machines in Dental Offices. Comparison to 3022

European Recommendations. The Heads of the European Radiological Protection Competent 3023

Authorities (HERCA) June, 2014 position statement on the use of hand-held x-ray equipment 3024

discourages their use except in special circumstances such as nursing homes, residential care 3025

facilities, or homes for persons with disabilities; forensic odontology; and military operations 3026

abroad without dental facilities (HERCA, 2014). The NCRP feels that the HERCA criteria are 3027

overly restrictive and that there are additional circumstances where the use of hand-held x-ray 3028

equipment may be suitable or advantageous (Section 7.3.1.1). The Committee anticipates the 3029

possibility that as hand-held x-ray equipment becomes less expensive, easier to use, and 3030

maintains or improves its safety characteristics, these units may supplant fixed or mobile x-ray 3031

equipment in general dental practice. 3032

3033

7.3.3 Position-Indicating Devices 3034

3035

The description and recommendations governing collimation of position-indicating devices 3036

are covered in Section 7.1.2 Hand-held x-ray units have built-in position indicating devices of 3037

various lengths. 3038

3039

7.3.4 Rectangular Collimation 3040

3041

Rectangular collimators are available as a part of the receptor-holding device on hand-held 3042

x-ray systems. 3043


132

3044

Recommendation 77. Rectangular collimation shall be used with hand-held devices 3045

whenever possible. 3046

3047

The description and recommendations that apply to rectangular collimation are covered in 3048

Section 7.1.3 3049

3050


133

8. Extraoral Dental Imaging 3051

3052

8.1 Panoramic 3053

3054


3056

Panoramic dental units produce a curved-surface tomogram of the oral and maxillofacial 3057

image. The tomographic focal trough follows the curved contours of the jaws, in general 3058

extending from ear to ear and from below the chin to the lower portion of the orbits. 3059

3060

Despite the advantage of imaging the entire dentomaxillofacial anatomy in one sweep, there 3061

are inherent limitations in the anatomical representations due to the very motion necessary to 3062

produce the panoramic image. Vertical image magnification is independent of horizontal 3063

magnification. The degree of magnification varies with position in the dental arch. This image 3064

distortion varies with anatomic area in a given patient and from patient to patient using the same 3065

panoramic x-ray machine. Furthermore, repeat images of the same patient may show differing 3066

distortion because of slight differences in patient positioning. In addition, image resolution is 3067

limited by the imperfect movement of source and image receptor required for the tomographic 3068

technique. Resolution with panoramic imaging (both film and digital) is less than with intraoral 3069

imaging (film and digital, respectively), resulting in diminished diagnostic accuracy of incipient 3070

caries, beginning periapical lesions, or marginal periodontal disease (Farman, 2007; Flint et al., 3071

1998; Rumberg et al., 1996; White and Pharoah, 2014). 3072

3073

Active development of improved projection geometry, digital tomosynthesis and the use of 3074

photon-counting detectors in panoramic imaging are likely to appear soon and should improve 3075

the quality and utility of panoramic imaging in dentistry. 3076

3077

8.1.1.1 Diagnostic Reference Levels and Achievable Doses. For panoramic imaging, NCRP 3078

Report No. 172 uses the air kerma-area product as the dose metric for its recommended DRL and 3079

AD. NCRP Report No. 172 recommends a DRL of 100 mGy cm2 and an achievable dose-area 3080

product of 76 mGy cm2 (NCRP, 2012b). Both are based upon European surveys. 3081


134

3082

8.1.1.2 Bitewings from Digital Panoramic Machines. Numerous manufacturers of panoramic 3083

equipment have devised imaging techniques that produce an image similar to a bitewing 3084

projection. The use of these images may be indicated for patients that cannot tolerate an intraoral 3085

bitewing radiograph. Situations such as hyperactive gag reflex, trismus, or large tori are 3086

suggested as indications for the use of these “extraoral bitewings.” Currently, there is only one 3087

study comparing the diagnostic efficacy of specific panoramic bitewing technique images with 3088

intraoral images and claimed that the intraoral bitewings were superior in caries detection. The 3089

data analysis was not robust, and, therefore, the conclusions are suggestive but equivocal 3090

(Kamburog-lu et al., 2012). Further studies are needed in order to make specific 3091

recommendations on the use of panoramic bitewing programs for caries detection, and likely 3092

periodontal evaluations. 3093

3094


3096

Panoramic dental units employ a stationary anode radiographic x-ray tube operating at tube 3097

peak potentials in the 70 to 100 kVp range. These systems utilize a narrow vertical collimator to 3098

produce a correspondingly narrow x-ray beam that passes through the patient. During a 3099

panoramic x-ray exposure the moving x-ray beam paints the image on the image receptor as the 3100

x-ray tube rotates around the patient. In the case of film-screen imaging, the screen-film cassette 3101

shifts during panoramic motion, resulting in exposure of the entire film. This produces a curved-3102

surface tomogram of the dentomaxillofacial structures. Panoramic x- ray beams must be no 3103

larger than the area of receptor exposed to the beam at any point in time. This area is defined by 3104

the slit collimator at the tube head. 3105

3106

Digital panoramic images can be produced by replacing the screen-film cassette with a 3107

cassette containing a photostimulable phosphor plate. Direct digital panoramic x-ray units utilize 3108

a narrow CCD or CMOS receptor array to create the familiar panoramic image. As with any 3109

digital imaging modality, digital panoramic x-ray unit displays allow the user to vary the 3110

brightness and contrast appearance of the image by adjusting window and level settings. Some 3111


135

direct digital panoramic units allow adjustment of the position of the image layer after the image 3112

has been acquired reducing the impact of patient positioning on image quality. 3113

3114

Recommendation 78. The x-ray beam for rotational panoramic tomography shall be 3115

collimated such that its vertical dimension is no greater than that required to expose the 3116

area of clinical interest and shall not exceed the size of the image receptor. 3117

3118

Older machines were designed for use with medium-speed calcium tungstate screen-film 3119

systems. In some cases the required reduction in x-ray output for use with high-speed rare-earth 3120

screen-film systems may only be accomplished by electronic modifications or addition of 3121

filtration at the x-ray tube head. Electronic modifications are permitted by the manufacturer if the 3122

modified device is cleared by the FDA through the 510(k) process. A manufacturer can modify 3123

an installed device in this manner. Added filtration, unless compensated by lower kilovoltage, 3124

hardens the beam spectrum, resulting in decreased image contrast. The dentist must be aware of 3125

these limitations in selecting and maintaining panoramic equipment or prescribing panoramic 3126

examinations. Otherwise, the limited diagnostic information obtained from the panoramic image 3127

may necessitate additional imaging. Periapical views alone may be adequate. 3128

3129

Recommendation 79. The fastest imaging system consistent with the imaging task 3130

(equal to or greater than ANSI 400 speed, or digital) shall be used for all panoramic 3131

radiographic projections. 3132

3133

Power for panoramic units may be an important factor. Panoramic units should not be on the 3134

same power supply as high power devices, e.g., elevators and air conditioners. Operation of other 3135

high power consuming devices can cause a fluctuation in the voltage to the panoramic unit and, 3136

hence, a fluctuation in the kilovoltage output. 3137

3138

Recommendation 80. Panoramic machines shall be on a dedicated electrical circuit. 3139

3140


136

8.2 Cephalometric 3141

3142


3144

Cephalometric equipment provides for positioning (and repositioning) of the patient together 3145

with alignment of beam, subject and image receptor. The source-to-skin distance is on the order 3146

of 150 cm or more, minimizing geometric distortion (magnification) in the image. It is frequently 3147

useful for the cephalometric image to show bony anatomy of the cranial base and facial skeleton 3148

plus the soft-tissue outline of facial contours, requiring image receptors of wide latitude. 3149

Additional filtration can further enhance soft tissue contours on the same image as the bone 3150

details (Section 8.2.2). 3151

3152

8.2.1.1 Diagnostic Reference Levels and Achievable Doses. For cephalometric radiography, 3153

NCRP Report No. 172 provides DRLs and ADs for entrance air kerma and air-kerma area 3154

product, both for the lateral projection. For the DRL, the report recommends, for the entrance air 3155

kerma, 0.14 mGy and for the air-kerma area product, 26.4 mGy cm2 for children and 32.6 mGy 3156

cm2 for adults. For ADs, the report recommends for the entrance air kerma 0.09 mGy and for the 3157

air-kerma area product 14 mGy cm2 for children and 17 mGy cm2 for adults. 3158

3159


3161

The area of clinical interest in cephalometric radiography is usually significantly smaller than 3162

the image receptor. Thus, collimation to the size of the image receptor does not meet the intent of 3163

restricting the beam to image only those structures of clinical interest (FDA/ADA, 2015a). The 3164

central axis of the beam is usually aligned through external auditory canals, which are positioned 3165

by the ear rods of the cephalostat. Imaging of structures superior to the superior orbital rim, 3166

posterior to occipital condyles, and inferior to the hyoid bone is clinically unnecessary. 3167

Therefore, the beam should be collimated such that these areas are shielded from exposure. Thus, 3168

the desired collimation is asymmetric, and the central axis of the beam is not centered on the 3169

image receptor. Further, it is usually desirable to image the soft-tissue facial profile along with 3170

the osseous structures of the face; this is accomplished by reducing exposure to the anterior soft 3171


137

tissues using filters that are placed between the x-ray source and the patient (Freedman and 3172

Matteson, 1976; Tanimoto, 1989). Placement of filters at the image receptor instead of at the x-3173

ray source does not reduce the dose to the patient and is inappropriate. 3174

3175

Recommendation 81. The fastest imaging system consistent with the imaging task 3176

(ANSI 400 speed or greater, or digital) shall be used for all cephalometric radiographic 3177

projections. 3178

3179

Recommendation 82. X-ray equipment for cephalometric radiography shall provide for 3180

asymmetric collimation to limit the beam to the area of clinical interest. 3181

3182

Recommendation 83. Filters for imaging the soft tissues of the facial profile together 3183

with the facial skeleton shall be placed between the patient and at the x-ray source 3184

rather than at the image receptor. 3185

3186


138

9. Cone-Beam Computed Tomography 3187

3188

3189

9.1 General Information 3190

3191

Dental cone-beam computed tomography (CBCT) has expanded the field of oral and 3192

maxillofacial imaging enhancing diagnostic information for the dental clinician through three-3193

dimensional volumetric image data of dental and maxillofacial structures (ADA 2012; Tyndall 3194

et al 2012). Since its introduction in 1997, CBCT has gained an increasing role in dentistry, 3195

transitioning from two- to three-dimensional imaging. By providing diagnostic images without 3196

magnification, distortion, superimposition, and misrepresentation of structures, CBCT imaging 3197

provides increased diagnostic accuracy, enhancing treatment outcomes. CBCT is also used by 3198

head and neck radiologists and ear-nose-throat, or otolaryngologist, physicians to assess midface, 3199

and middle and inner ear, throat, and other skull base structures (Cakli et al., 2012; Miracle and 3200

Mukherji, 2009a; 2009b). 3201

3202

The value of CBCT image data may be augmented with sophisticated software applications 3203

which enhance images and permit merging of images with complementary data sets. An example 3204

of this is the combination of CBCT images with photographic images of the teeth and soft tissues 3205

acquired with intraoral cameras. Merging of these data sets provides an accurate representation 3206

of the hard and soft tissues and their relationship to each other, enabling visualization of not only 3207

implant position, but also the final restoration. In addition, CBCT scans through computer aided 3208

design and manufacturing (CAD-CAM) technology can provide surgical guides for implant 3209

placement. Several CBCT equipment manufacturers and software vendors provide the capability 3210

of integrating 3D scans with CAD-CAM technology by CBCT impression scanning of 3211

conventional dental impressions so that crowns can be designed and milled chairside. 3212

3213

Many CBCT systems present an appearance that is similar to panoramic dental units. Indeed 3214

there are many similarities, including patient positioning, approximate imaging time, kilovoltage 3215

and milliamperage. From an imaging perspective, the most substantive difference is the 3216

availability of reconstructed images of various slice thicknesses, viewable in many planes, 3217


139

orientations or 3-dimensional renderings . From a safety perspective, substantial differences in 3218

the size and shape of the x-ray beam affect the dose to the patient, dose to the operator, and 3219

people who may be nearby. Median effective dose imparted by a standard CBCT examination 3220

with a medium field of view is ~107 µSv. Typical conventional panoramic doses are 20 % of this 3221

value (Ludlow et al., 2015). 3222

3223

CBCT scanners differ from conventional CT scanners [multi-detector CT (MDCT)] primarily 3224

in image data acquisition. In a conventional CT scanner, the x-ray beam emerges from the x-ray 3225

source as a flat fan beam. Data is acquired as a series of consecutive slices of the patient’s head 3226

acquired from multiple rotations of the x-ray source around the patient. In some MDCT scanners 3227

the width of the beam can be as large as 160 mm, enabling acquisition of individual organs in a 3228

single sweep. In contrast, the x-ray beam in a dental CBCT scanner diverges from the x-ray 3229

source as a cone or pyramid. Data is acquired as a series of area projections made with small 3230

angular differences as the beam rotates around the patient’s head. Scanners acquire image data 3231

(termed basis images) through a single rotation of at least 180 degrees and up to 360 degrees 3232

around the patient’s head. Images are reconstructed through algorithms, producing three-3233

dimensional images. Due to hardware differences CBCT scan acquisition times may range from 3234

10 to 70 s. Similar volume sizes may be acquired with MDCT, while decreasing acquisition 3235

times to as little as 1 s or less. The radiation dose to the patient from CBCT may be up to 10 3236

times less than that from a similar MDCT examination; however, some CBCT units and 3237

examination protocols produce doses comparable to MDCT scans (Ludlow and Ivanovic. 2008) 3238

and, in some cases, doses which may exceed those of MDCT scans (Ludlow et al., 2014). 3239

3240

Most CBCT systems employ fixed anode x-ray tubes similar to those in panoramic x-ray 3241

machines, operating in the 70 to 100 kVp range. Instead of a narrow vertical aperture, CBCT 3242

systems employ collimation that permits larger area exposures. These beam limiting devices 3243

have varying degrees of adjustment selectable by the operator. Several manufacturers provide 3244

systems with a choice of several beam sizes, allowing the operator to select both beam height 3245

and width appropriate for few teeth or the full maxillofacial region. 3246

3247


140

CBCT image receptors are essentially direct digital radiography receptors that employ flat 3248

panels. The larger image receptors are generally capable of collecting smaller x-ray fields of 3249

view. 3250

3251

9.1.1 Dose Comparisons for CBCT and MDCT Machines 3252

3253

Although CBCT radiation doses are usually less than those produced during MDCT, the 3254

radiation doses to tissue are usually higher than those of conventional dental radiographic 3255

modalities. The effective dose of an optimized CBCT examination is 2 to 5 % of a conventional 3256

CT of the same region, but approximately seven times greater than that from a panoramic image 3257

(Ludlow and Ivanovic, 2008). 3258

3259

Table 9.1 shows approximate effective doses from CBCT and MDCT units, operating with 3260

different fields of view. The values are averaged from wide ranges of exposures, depending on 3261

the specific units measured and the acquisition parameters. 3262

3263

Recommendation 84. CBCT should be used for cross sectional imaging as an alternative to 3264

conventional computed tomography when the radiation dose of CBCT is lower and the 3265

diagnostic yield is at least comparable. 3266

3267

Doses for CBCT devices vary widely, but median, typical protocol adult doses are ~60 µSv 3268

for small FOVs, 107 µSv for medium FOVs and 151 µSv for large FOVs (Figure 9.1). Similar 3269

patterns of increased dose with increased FOV size are seen for child phantom exposures (Figure 3270

9.2). 3271

3272

In summary, Figures 9.1 to 9.3 show that the effective dose varies by FOV size for both 3273

adults and children. Furthermore, these also show the relative contributions of bone marrow, 3274

brain, and thyroid decrease with decreasing FOV size. However, the relative contributions of 3275

salivary gland and remainder tissues increase with decreasing FOV size. 3276

3277

3278


141

3279

TABLE 9.1—Approximate effective doses from CBCT and MDCT examinations. 3280

Examinationa Effective Dose

(µSv)

CBCT small FOV 60

CBCT medium FOV 107

CBCT large FOV 151

MDCT mandible (isotropic voxels) 427

MDCT jaws 697

MDCT head 1,088

3281

aCBCT doses are from Ludlow et al., 2015. MDCT doses are from Tables F1 and F2 in Appendix F 3282


142

3283

3284

3285

3286

3287

3288

3289

3290

3291

3292

Fig. 9.1. Effective doses of typical CBCT examinations by field of view size for adult 3293

phantom exposures. Median and inter-quartile spread are shown (Ludlow et al., 2015). 3294

3295


143

3296

3297

3298

3299

3300

3301

3302

3303

3304

3305

Fig. 9.2. Effective doses of typical CBCT examinations by field of view size for child 3306

phantom exposures. Median and inter-quartile spread are shown (Ludlow et al., 2015). 3307

3308

3309


144

3310

3311

3312

3313

3314

3315

3316

3317

3318

3319

3320

Fig. 9.3. Relative organ contributions to effective dose by FOV size (Ludlow et al., 2015). 3321

3322


145

3323

Recommendation 85. CBCT examinations shall use the smallest field of view (FOV) and 3324

technique factors that provide the lowest dose commensurate with the clinical purpose. 3325

3326

9.1.2 Use of Simulated Bitewing, Panoramic, and Cephalometric Views from CBCT Data 3327

3328

Cephalometric images produced with conventional x-ray equipment using rare earth screens 3329

and matched film or digital technologies produce typical adult effective doses around 5 µSv. 3330

Standard panoramic doses vary for different devices, but typical adult doses are between 15 and 3331

25 µSv. 3332

3333

While bitewing projections, panoramic image layers, and cephalometric projections can be 3334

reconstructed from a CBCT image volume, low resolution and artifact from nearby metal 3335

restorations limit the usefulness of these reconstructions for diagnosis of dental caries. In 3336

addition, radiation doses are substantially greater than needed to produce conventional 3337

panoramic and cephalometric images (Table 9.2). As such, they cannot replace the use of 3338

conventional bitewing, panoramic, and cephalometric images in dental practice. 3339

3340

Table 9.2 presents patient effective doses reported in the literature for CBCT, compared with 3341

other common x-ray imaging exams. 3342

3343

Recommendation 86. CBCT examinations shall not be obtained solely for the purpose 3344

of producing simulated bitewing, panoramic, or cephalometric images. 3345

3346

9.1.3 Number of CBCTs in the United States and Growth Rate 3347

3348

The just-completed 2015 Nationwide Evaluation of X-Ray Trends (NEXT) survey examined 3349

the use of x-ray diagnostics in dentistry (Farris and Spelic, 2015). Preliminary analysis estimates 3350

there are 5,500 dental CBCT units in the United States. It also estimates 300,000 pediatric CBCT 3351

examinations annually and 3,876,000 adult and adolescent CBCT examinations annually. 3352

3353


146

3354

TABLE 9.2—Comparison of effective doses for CBCT. MDCT, and conventional radiographic 3355

examinations (EC, 2012). 3356

3357

3358

3359

3360

3361

3362

3363

3364

3365

3366

3367

Modality Median (µSv) Range (µSv)

CBCT, dento-alveolar 61 11 – 674

CBCT, craniofacial 87 30 – 1,073

Intraoral radiograph — <1.5

Panoramic radiograph — 2.7 – 24.3

Cephalometric radiograph — <6.0

MDCT maxillo-mandibular — 280 – 1,140


147

3368

CBCT in dentistry has grown rapidly over the past decade through its features of short 3369

scanning times, increased diagnostic yield relative to radiation exposure, high resolution, and 3370

geometric accuracy. A 2011 study found 15 different manufacturers offer 24 CBCT models in 3371

the United States and many more worldwide (Ludlow, 2011). This suggests an impressive 3372

continuing demand for this technology. With its increasing application in dentistry, there has 3373

been a focus to develop guidelines for its safe and effective use, along with the development of 3374

selection criteria, quality assurance programs and clinical optimization in through evidence based 3375

research. National and international groups have provided basic principles (White and Pharoah, 3376

2014), selection criteria and professional guidelines (EC, 2012) for CBCT in dentistry. Position 3377

statements (AAE/AAOMR, 2011; AAOMR, 2013; Tyndall et al., 2012) and CBCT guidance 3378

documents (EC, 2012) have been developed by dental specialty organizations. 3379

3380

9.1.4 Efforts Regarding CBCT in Europe—SEDENTEXCT and Evidence-Based Guidelines 3381

3382

The SEDENTEXCT project of the European Commission (2008 to 2011) was a widespread 3383

effort by stakeholders throughout the European Union (partnership from the United Kingdom, 3384

Greece, Romania, Belgium, Sweden, and Lithuania) to develop guidelines for the safe and 3385

effective use of cone beam CT in maxillofacial imaging. The final report, entitled Radiation 3386

Protection No 172. Cone Beam CT for Dental and Maxillofacial Radiology. Evidence-Based 3387

Guidelines was published in 2012 (EC, 2012) and contains exhaustive data and discussion on all 3388

aspects of CBCT imaging, including radiation dose and risk, basic principles of CBCT imaging, 3389

selection criteria, quality assurance, and protection and training of staff. Additionally, a CBCT 3390

quality assurance protocol and phantom were developed. The reader is referred to this robust 3391

document for further details as well as the SEDENTEXCT website www.sedentexct.eu. A 3392

comprehensive review of CBCT indications and use has been published recently (Horner et al., 3393

2015). 3394

3395


148

9.1.5 Patient Selection Criteria for CBCT 3396

3397

The CBCT examination is a complementary examination to, not a replacement for, two-3398

dimensional imaging modalities. Just as for other dental radiographic examinations, justification 3399

for each patient should be based on their imaging history and the diagnostic yield not achievable 3400

with the 2D modalities. The examination is justified if the anticipated diagnostic yield outweighs 3401

the risks associated with radiation (AAOMR, 2008; ADA, 2012; EADMFR, 2009; Farman and 3402

Scarfe, 2006; White, 2009). CBCT should only be used when the question for which the imaging 3403

is required cannot be answered adequately by conventional, lower dose dental radiography, 3404

applying the ALARA principle (NCRP, 2003). 3405

3406

Prior to the acquisition of a CBCT examination, a dental examination by the ordering 3407

provider should be completed, with a review of the patient’s medical history, as well as the 3408

medical and dental imaging history. Previously acquired dental and medical imaging, which falls 3409

short of yielding the necessary clinical information, may justify the need for the CBCT 3410

examination (ADA, 2012; Farman and Scarfe, 2006). The decision about the clinical indication 3411

for CBCT is the professional determination of the treating clinician. 3412

3413

Recommendation 87. CBCT shall not be used as the primary or initial imaging 3414

modality when an alternative lower dose imaging modality is adequate for the clinical 3415

purpose. 3416

3417

Some of the evidence-based specific indications for CBCT imaging follow. 3418

3419

9.1.5.1 Implants. The initial overall evaluation of a potential dental implant patient should be 3420

completed using panoramic imaging. CBCT is widely considered as the imaging modality of 3421

choice for preoperative, cross-sectional imaging of potential implant sites (Tyndall et al., 2012). 3422

CBCT demonstrates bone volume, quality or topography, and relationships to vital anatomical 3423

structures such as nerves, vessels, nasal floor, and sinus floors. Implant planning using CBCT 3424

must take into consideration the restorative process for which implants are being planned. For 3425

this reason, when treatment of multiple implant sites is being planned, radiographic guides 3426


149

should be considered prior to any CBCT for implant planning. This also insures that patient 3427

radiation dose is optimized when planning multiple sites. 3428

3429

CBCT may also be considered when clinical conditions suggest a need for augmentation or 3430

site development before placement of implants. CBCT should be considered if bone 3431

reconstruction and augmentation procedures have been performed. In the absence of clinical 3432

signs or symptoms, intraoral periapical imaging should be used for the postoperative assessment 3433

of implants. Panoramic radiographs may be indicated for more extensive implant therapy cases. 3434

CBCT should be considered if implant retrieval is anticipated (ADA, 2012; Almog et al., 1999; 3435

Benavides et al., 2012; Ebrahim et al., 2009; Harris et al., 2012; Tyndall and Rathore, 2008; 3436

Tyndall et al., 2012; Wang et al., 2011). 3437

3438

Use of CBCT immediately post-operatively may be indicated if the patient presents with 3439

implant mobility or altered sensation, particularly if the fixture is in the posterior mandible 3440

(Harris et al., 2012; Tyndall et al., 2012). CBCT imaging is not indicated for the periodic review 3441

of clinically asymptomatic implants. 3442

3443

9.1.5.2 Oral and Maxillofacial Surgery. Many surgical procedures involving bony components 3444

of the jaws and maxillofacial structures may benefit from CBCT. CBCT images often provide 3445

valuable information for surgical planning and follow-up. Before ordering CBCT imaging, the 3446

clinician should evaluate other imaging modalities requiring less radiation that may provide 3447

sufficient diagnostic information. Where soft tissue evaluation is essential to diagnosis and 3448

treatment planning, CBCT is inappropriate because of poor soft tissue resolution. In such 3449

circumstances, MDCT, MRI, or ultrasound are likely to be more appropriate and efficacious. 3450

3451

In treatment planning the surgical removal of third molars or other impacted teeth, 3452

conventional imaging may suggest a direct inter-relationship between the teeth and surrounding 3453

key anatomic areas such as the maxillary sinus, adjacent teeth, and mandibular nerve. Limited 3454

CBCT may be indicated for pre-surgical assessment of an impacted or unerupted tooth as an 3455

adjunct to conventional imaging (Becker et al., 2010; Neugebauer et al., 2008; Suomalainen 3456

et al., 2010; White, 2008). 3457


150

3458

Limited-volume, high-resolution CBCT may also be indicated for evaluation of intraosseous 3459

pathological entities when the initial imaging modality used for diagnosis and staging does not 3460

provide satisfactory three-dimensional information (Rosenberg et al., 2010; Simon et al., 2006; 3461

White, 2008). In evaluating lesions in the maxilla and mandible, intraoral or panoramic 3462

radiographs show only two dimensions of the lesion. CBCT imaging may provide additional 3463

information on the extent of the lesion, cortical expansion, internal or external calcifications, and 3464

proximity to teeth as well as other vital anatomy. In surgical planning, a lesion must be measured 3465

from different angles. CBCT measurements, when compared to the gold standard dry skull have 3466

been shown to be acceptably accurate with <1 % error (Ludlow et al., 2007; Stratemann et al., 3467

2008). 3468

3469

Initial assessment of a simple dental or jaw fracture, and in some cases complex jaw fracture, 3470

may also be achieved with periapical or panoramic radiographs. However, vertical root fracture 3471

(Wang et al., 2011) or multiple jaw fractures (Palomo and Palomo, 2009; Shintaku et al., 2009) 3472

may be better visualized with CBCT images. In such cases, CBCT may be a valid alternative 3473

imaging modality to MDCT, considering image quality and radiation dose (Tyndall, 2008; 3474

White, 2008). 3475

3476

CBCT may be utilized for pre-operative orthognathic surgical planning (Farman and Scarfe, 3477

2006). DICOM data from CBCT can be used to fabricate physical stereolithographic models or 3478

to generate virtual 3D models (O’Neil et al., 2012), which have been useful for orthognathic 3479

assessment of morphology, spatial relationship, and growth and developmental anomalies. The 3480

3D reconstructions from CBCT are useful in the diagnosing and treatment planning of facial 3481

asymmetry cases. Follow-up CBCT imaging is useful in evaluating the success of orthognathic 3482

surgery, as well as to measure the displacement of the surgical segments in all three orientations 3483

(Cevidanes et al., 2007). 3484

3485

9.1.5.3 Periodontal Indications. CBCT is not indicated for routine evaluation of the 3486

periodontium. When clinical examination and conventional imaging studies do not provide the 3487

information needed for the management of infra-bony defects and furcation lesions, limited 3488


151

volume, high resolution CBCT may be indicated (Tyndall et al., 2008; Vandenberghe et al., 3489

2008; Walter et al., 2010; White, 2008). In CBCT fields of view that include images of teeth, 3490

periodontal bone should be evaluated for periodontal disease. 3491

3492

9.1.5.4 Endodontic Indications. CBCT is not indicated as a standard method for demonstration of 3493

root canal anatomy. Limited volume, high resolution CBCT may be indicated when conventional 3494

intraoral imaging provides inadequate information, contradictory clinical signs and symptoms 3495

are present, evidence of inflammatory root resorption, internal resorption, suspected root 3496

fracture, combined periodontal-endodontic lesions, perforations or atypical pulp anatomy 3497

(AAE/AAOMR, 2011; 2015; Tyndall et al., 2008). In CBCT fields of view that include images 3498

of teeth, periradicular bone should be evaluated for periapical disease. 3499

3500

9.1.5.5 Temporomandibular Joint Indications. The high spatial resolution of CBCT makes it 3501

ideal for detailed evaluation of osseous changes in the temporomandibular joint. While 3502

panoramic imaging often gives a limited overview of the status of these bone components, 3503

CBCT is indicated when a more detailed examination is needed. This would be most often 3504

indicated for severity assessment of arthritides, evaluation of erosive or proliferative bone 3505

lesions, or intracapsular condylar trauma (Alexiou et al., 2009; dos Anjos Pontual et al., 2012; 3506

Librizzi et al., 2011; Palomo and Palomo, 2009). 3507

3508

CBCT is not appropriate for evaluation of internal derangements due to its poor contrast 3509

resolution and inability to demonstrate the soft tissue structures (Marques et al., 2010). 3510

3511

9.1.5.6 Caries Diagnosis Indications. CBCT is not an acceptable diagnostic examination for 3512

occlusal (Rathore et al., 2012) or proximal (Wenzel et al., 2014) carious lesions (Section 9.1.2). 3513

3514

9.1.5.7 Sinonasal Evaluation Indications. Spatial and contrast resolution of CBCT is acceptable 3515

for evaluating osseous and gross soft tissue changes of the sinusonasal complex (Tadinada, 3516

2015b; Xu et al., 2012). In particular, details of the integrity and configuration of the borders of 3517

these structures are clearly shown on CBCT images. Compared to current gold standard of 3518

sinonasal imaging by MDCT, CBCT provides substantial dose reduction (Guldner et al., 2013) . 3519


152

3520

Compared to panoramic radiographs, CBCT provides better information about the 3521

relationship of the sinus floor to the roots of molars (Jung and Cho, 2012; Shahbazian et al., 3522

2014). Inflammatory diseases of the sinus can be evaluated with CBCT (Ritter et al., 2011). 3523

Sinusitis related to apical periodontitis can be identified with CBCT (Lu et al., 2012; Maillet 3524

et al., 2011; Shanbhag et al., 2013). However, soft tissue tumors, fluid or blood cannot be 3525

differentiated based solely on CBCT (Ritter et al., 2011). 3526

3527

9.1.5.8 Craniofacial Disorders Indications. Compared to traditional dental imaging, CBCT can 3528

provide additional information for the treatment planning and complex management of 3529

craniofacial disorders and syndromes. CBCT volume renderings allow complete representation 3530

of the altered three-dimensional anatomy that is the hallmark of most craniofacial disorders. 3531

Additionally, CBCT is useful for evaluating positions and orientations of impacted teeth, extent 3532

and involvement of bony structures with palatal or alveolar cleft, and variations of normal bony 3533

structures (Kuijpers et al., 2014). 3534

3535

9.1.5.9 Orthodontics. Children and young adolescents, who comprise the substantial majority of 3536

patients receiving orthodontic treatment, have increased sensitivity to cancer induction by 3537

radiation. Estimates range from at least two times greater sensitivity (NA/NRC, 2006; 3538

UNSCEAR, 2013) to 10 times greater than adults (NA/NRC, 2006), depending on the tissue 3539

irradiated and the age of the patient. Additionally, most orthodontic CBCT imaging, excluding 3540

small volume acquisitions for localizing impacted teeth, involves large fields of view, including 3541

structures in the skull base and neck. Thus, it is incumbent on professionals using CBCT to 3542

image children and young adolescents to be especially judicious in their use of this imaging 3543

modality. 3544

3545

The recent position paper of the AAOMR presented the following evidence-based guidelines 3546

for CBCT use in orthodontics (AAOMR, 2013): 3547

3548

1. image appropriately according to clinical condition; 3549

2. assess the radiation dose risk; 3550


153

3. minimize patient radiation exposure; and 3551

4. maintain professional competency in performing and interpreting CBCT studies . 3552

3553

These AAOMR guidelines are consistent with the 2012 American Dental Association (ADA) 3554

advisory statement regarding the use of CBCT in dentistry and the general principles 3555

promulgated in the joint ADA-FDA guidelines (ADA, 2015a; 2015b). However, they are less 3556

explicit than the recommendations found in the European SEDENTEXCT report (EC, 2012). 3557

The SEDENTEXCT guidelines clearly state that “CBCT examinations should not be repeated 3558

‘routinely’ on a patient without a new risk-benefit assessment having been performed, and that 3559

using CBCT for routine or screening imaging is unacceptable practice. 3560

3561

Recommendation 88. CBCT examinations shall not be used for routine or serial 3562

orthodontic imaging. 3563

3564

9.1.5.10 Obstructive Sleep Apnea. CBCT can be useful in the management of obstructive sleep 3565

apnea. CBCT volumes have been used to assess dimensional and morphologic changes in the 3566

upper airway, as well as to assess changes in these parameters after appliance or surgical therapy. 3567

While current studies suggest such efficacy of CBCT imaging, further evidence is needed to 3568

document its impact on patient outcomes (Alsufyani et al., 2013). 3569

3570

9.2 Equipment and Facilities 3571

3572

The amount of scattered radiation produced when a radiation beam is incident on the human 3573

head at a given distance depends on the kilovoltage, milliampere-seconds, and the volume of 3574

tissue irradiated. Panoramic dental radiographic units produce relatively little scatter because the 3575

beam is only ~3 ・ 100 mm at the patient's head. In CBCT systems, the x-ray beam may entirely 3576

cover the maxillofacial region and is commonly as large as 80 ・ 80 mm at the patient's head. 3577

Scattered radiation exposure at a fixed distance (e.g., 1 m) will be approximately 300 times 3578

higher for a CBCT system, compared with a panoramic x-ray system. 3579

3580


154

Scattered radiation will increase linearly with the workload, i.e., the total milliampere-3581

seconds used per week. Panoramic dental radiography is a well-established imaging modality, 3582

and workloads may be reliably estimated from the literature (MacDonald et al., 1983; Reid and 3583

MacDonald, 1984; Reid et al., 1993) CBCT, however, is a relatively new imaging modality and 3584

its clinical indications continue to expand. It is likely that increased efficacy of CBCT will result 3585

in continued increases in its clinical utility. As new indications for appropriate use of CBCT are 3586

added, the CBCT workload in dental clinics will increase proportionally. 3587

3588

Preliminary assessment of the data from the 2015 NEXT Survey (Farris and Spelic, 2015) 3589

show proportionately lower exposures for children compared with adults: average milliamperage 3590

for children, 6.8 mA, and for adults, 8.3 mA; scan time for children, 7.7 s, and for adults, 12.1 s. 3591

The substantial majority of examinations were performed on adults: 11.6 per week versus 1.3 per 3592

week for children. 3593

3594

Although it may be tempting to physically replace a panoramic radiographic device with a 3595

CBCT system by simply removing the old unit and installing the CBCT gantry, this method 3596

creates the potential for substantial radiation exposure to people in the vicinity of the CBCT 3597

system. Some panoramic x-ray units have been installed in dedicated, shielded dental x-ray 3598

rooms. It is not uncommon, however, to find panoramic radiographic units installed on an open 3599

space within the dental suite, often a remote corner or alcove. The small field size and resultant 3600

minimal scatter from panoramic units may permit such installations while maintaining radiation 3601

exposures to persons in the vicinity well below permissible levels. 3602

3603

However, CBCT systems placed in the location formerly occupied by a panoramic dental 3604

unit will generate substantially more scattered radiation per exam, and may not result in 3605

exposures that are ALARA. The combination of substantially greater volume of tissue irradiated 3606

and potentially much higher workload must be considered when assessing radiation safety 3607

requirements for a CBCT installation. It is preferable to install a CBCT unit in a dedicated room 3608

that meets these safety requirements. 3609

3610


155

Using the NEXT data of 11.6 adult CBCT examinations per week and 1.3 pediatric CBCT 3611

examinations per week, and assuming a very heavy workload and tripling these exam 3612

frequencies, the resulting number of exams would be 45 per week. Even with this estimated 3613

weekly workload, the occupational exposure would be well below the regulatory limits for a 3614

well-designed CBCT facility. However, for a poorly designed CBCT installation, exposures to 3615

the general public, office staff, and occupationally exposed personnel could potentially exceed 3616

the respective regulatory maximums. Hence, we recommend an initial radiation shielding design 3617

be performed by a qualified expert before installation of a CBCT, and that the qualified expert 3618

annually assess the radiation safety of the installation by validating the workload assumptions 3619

and recalculating exposures when indicated. 3620

3621

9.2.1 Radiation Dose Structured Report Equivalent Needed for CBCT 3622

3623

Modern medical CT units provide a DICOM radiation dose structured report that allows 3624

determination of the patient dose from individual examinations. Differences in acquisition 3625

physics and data structures between CBCT and MDCT prevent the same method of 3626

determination and require development of a new method of determination for CBCT. 3627

3628

In addition, there is presently much discussion among medical and health physicists, and 3629

radiation biologists, regarding effective dose versus dose area product as a metric for expressing 3630

dose and risk to the patient from a particular examination (NCRP, 2012b). In this report, we have 3631

elected to use effective dose because it provides units in terms of risk and because the 3632

presentation of dose and risk in the dental literature is entirely in terms of effective dose. 3633

3634

While the use of dose area product (DAP), also known as the Kerma Area Product (PKA) has 3635

been advocated as a measure of dose for CBCT units, their accuracy as a measure of risk for the 3636

small volumes acquired for dental diagnostic imaging is debatable (EC, 2012; HPA, 2010). In 3637

relating DAP to effective dose, a conversion coefficient must be used. Illustrating this problem, 3638

one study using a single CBCT unit calculated conversion coefficients for DAP to effective dose 3639

for large to small FOVs and found that a 3.8-fold range of values was required for different field 3640

sizes and anatomic locations (Kim et al., 2014). A 7.5-fold range of DAP to effective dose ratios 3641


156

were calculated from the adult phantom data in a recent study encompassing a large number of 3642

measurements on CBCT devices of varying beam energies (Ludlow et al., 2014). The use of 3643

volume height in the place of projection area in this study resulted in statistically improved 3644

accuracy in the estimation of effective dose but still led to a range in the conversion coefficient 3645

of 2.4-fold for adult phantom imaging. This improvement is intriguing as beam height may be 3646

easily substituted for beam area in dose calculations. While use of volume height in place of area 3647

in dose calculation warrants further investigation, it is apparent that development of universal 3648

conversion coefficients to translate simple measures of exposure to patient dose with the goal of 3649

risk estimation is problematic. In addition to Kerma Area Product or dose area product or dose 3650

height product (DHP) for different scan parameters, it would be useful for manufacturers to 3651

provide machine specific coefficients for the conversion of PKA, DAP or DHP into effective dose 3652

so that an estimate of risk associated with an examination would be available for the clinician 3653

and patient. 3654

3655

Recommendation 89. Manufacturers should develop PKA values for CBCT acquisitions 3656

and provide conversion coefficients or other dose metrics necessary for the calculation 3657

of effective dose in order to allow an estimate of risk for each acquisition. 3658

3659

9.2.2 Advantages of Pulsed Systems over Continuous Radiation Exposure Systems 3660

3661

Dental radiographic x-ray generators use transformers and other circuits to step-up the 120 3662

volts AC source provided by the utility to the kilovoltage range needed for x-ray imaging. In 3663

recent decades, dental radiographic x-ray generators have most often been designed to produce 3664

relatively continuous waveforms at a fixed milliamperage. Varying the exposure time is typically 3665

used to change the amount of radiation used to expose the patient and create the image. For ease 3666

of use and consistency, many generators display different patient sizes (pediatric, small, medium 3667

and large adult) so that the operator may select the most appropriate technique. 3668

3669

Most image receptors used in CBCT applications are unable to record x-ray exposure during 3670

the period when the image detector integrates (processes) the x-ray energy absorbed in individual 3671

receptor pixels and transfers this signal to the computer. Continued x-ray exposure during signal 3672

integration contributes to patient dose but adds nothing to image formation. To eliminate this 3673


157

unnecessary patient exposure, many CBCT units utilize a pulsed x-ray source, where x-ray 3674

emission is intermittently turned off during the image acquisition process. This feature can 3675

significantly reduce patient exposure when appropriately applied and is explicitly engineered 3676

into CBCT equipment. For example, a pulsed generator operating at 7 mA for 20 s may deliver 3677

substantially <140 mAs. This methodology for pulsing the x-ray beam in sequence with active 3678

pixel measurement should not be confused with half-wave rectification found in some older 3679

dental x-ray machines. Whether an x-ray generator produces continuous or pulsed x-ray beams, 3680

it is critical that the total dose be measured by the qualified expert and compared with published 3681

benchmarks to assure that patient image quality is optimized and the dose ALARA. The 3682

qualified expert should ensure that his/her measuring instrumentation is capable of capturing data 3683

from both continuous and pulsed x-ray systems. 3684

3685

9.2.3 Advantages of 180 Degree Scan versus 360 Degree Scan 3686

3687

Some newer CBCT machines have an optional acquisition mode that rotates the x-ray source 3688

and detector through a 180 degree arc rather than a 360 degree arc. This reduces the radiation 3689

dose by close to 50 % at the expense of a somewhat noisier image. However, an in vitro study on 3690

detection of artificially created TMJ bone defects (Yadav et al., 2015) showed no differences in 3691

detection efficacy between the two rotational acquisition modalities. If the results of this study 3692

are confirmed and are shown to apply to other diagnostic tasks, such as implant site dimensional 3693

measurements and precise relationships between mandibular third molar roots and mandibular 3694

canals, this could become the technique of choice in some well-defined situations to substantially 3695

reduce radiation dose while maintaining diagnostic efficacy. 3696

3697

9.2.4 Location of Equipment and Requirements for Shielding 3698

3699

Requirements for equipment location and shielding for CBCT facilities are based upon CT 3700

requirements as promulgated in NCRP Report No. 147 (NCRP, 2004a). There are special 3701

considerations for CBCT operation, based on machine location, machine settings, imaging 3702

geometry, position of the patient, and workload. These issues are dealt with in general terms in 3703

Sections 4.1.1 and 4.5.1, and are given in greater detail in Appendix D. 3704


158

10. Administration and Education 3705

3706

10.1 Administrative and Regulatory Considerations 3707

3708

Regulatory, accreditation, and professional organizations provide the oversight and guidance 3709

needed to meet accepted image quality standards, safety standards, and standards of care. The 3710

requirements of such bodies are accomplished through the practitioner’s or facility’s quality 3711

control program (NCRP, 2010). Operators of radiation-emitting devices such as dental x-ray 3712

machines must be familiar with and comply with applicable federal, state, and local regulations. 3713

3714

10.1.1 Compliance with FDA Medical Device Regulations and Electronic Product Radiation 3715

Control Performance Standards 3716

3717

The FDA Center for Devices and Radiological Health “is responsible for regulating firms 3718

who manufacture, repackage, relabel, and-or import medical devices sold in the United States,” 3719

including dental x-ray unit (http//www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/ 3720

Overview/default.htm). 3721

3722

Legally marketed dental x-ray devices comply with federal regulations for medical devices 3723

and radiological health. Under the medical device regulations (21 CFR Subchapter H), dental x-3724

ray devices must be cleared by the FDA before being offered for sale in the United States. These 3725

regulations are intended to provide reasonable assurance of safety and effectiveness for medical 3726

devices marketed in the United States. To verify that a particular device has been reviewed by 3727

the FDA, practitioners can search the FDA’s online searchable database for Medical Device 3728

Premarket Notifications at http//www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfPMN/pmn.cfm. 3729

3730

The radiological health regulations (21 CFR Subchapter J) are intended to protect the public 3731

from hazardous or unnecessary radiation exposure from radiation emitting-electronic products. 3732

These regulations require that manufacturers of radiation emitting electronic products adhere to 3733

specific reporting, recordkeeping, and labeling requirements as well as comply with applicable 3734

performance standards in 21 CFR 1020.30 through 1020.33. Diagnostic x-ray devices that 3735


159

comply with the radiological health regulations will include certification, identification, and 3736

warning labels. These labels will be permanently affixed, legible, and readily accessible to view 3737

when the device is fully assembled for use [21 CFR 1010.2(b) and 1010.3(a)]. Figure 10.1 shows 3738

identification and certification labels. 3739

3740

A radiation-emitting device that meets the FDA requirements will be deemed “cleared by the 3741

FDA.” It is worth noting that the appropriate terminology uses the word “cleared”. The FDA 3742

does not “approve” radiation-emitting devices. An FDA cleared device meets the stringent 3743

design requirements necessary to minimize the dose to the operator with proper use of the 3744

equipment. 3745

3746

When new technology is introduced, especially in the current global marketplace, it is 3747

critical that buyers and operators be certain that the devices they are purchasing and using are 3748

cleared by the FDA. 3749

3750

10.1.2 General Considerations 3751

3752

The following are good imaging practices in a dental setting: 3753

3754

1. Clear policies and procedures governing safe and effective use of radiation in the dental 3755

practice. For example, quality assurance and quality control (Section 5.2), and radiation 3756

safety of the patient and operators (Sections 4.4 and 4.5). 3757

2. Selection criteria for all imaging procedures (see Sections 4.4.1 for general radiology and 3758

9.1.5 for CBCT). 3759

3. Recording of the date, number, types, retakes, and operator for each examination. 3760

4. Maintenance of all records at least as long as required by the administrative authority, 3761

e.g., state dental or medical board, or other government agencies. 3762

3763


160

3764

3765

3766

3767

3768

3769

3770

3771

3772

3773

3774

3775

3776

3777

3778

3779

3780

3781

3782

Fig. 10.1. FDA required identification and certification x-ray equipment labels. Top and 3783

middle photos show the two labels required for FDA-cleared equipment (indicated by 3784

compliance with DHHS Rules 21CFR, subchapter J). Bottom photo shows placement of the two 3785

labels on an x-ray tube. 3786

3787


161

10.1.3 Hand-Held X-Ray Devices 3788

3789

There are several handheld x-ray units for sale in the United States. The design of the internal 3790

components of these machines varies tremendously, as do the dose levels and exposure times. 3791

FDA’s performance standards for intra-oral imaging devices, including hand-held systems are 3792

included in sections 21 CFR 1020.30 and 1020.31. These performance standards address 3793

requirements such as control and indication of technique factors, reproducibility, and source-to-3794

skin distance. Some units offered for sale, primarily through the Internet, have not been cleared 3795

by the FDA and present radiation hazards to the operator and the patient (Sections 7.3.2.3 and 3796

10.1.1). 3797

3798

Recommendation 90. Only hand-held dental x-ray devices cleared by FDA for sale in 3799

the United States shall be used. 3800

3801

Some regulatory organizations have implemented rules and regulations preventing the user 3802

from holding the x-ray tube. These rules and regulations are unnecessary and impractical for 3803

FDA-cleared hand-held x-ray systems. The risks associated with holding the x-ray tube are 3804

mitigated by properly designed and labeled hand-held x-ray systems. Because properly designed 3805

and labeled hand-held systems can offer a cost-effective, flexible, and safe alternative to wall-3806

mounted systems, these rules and regulations should be relaxed for equipment that is designed to 3807

be hand-held. 3808

3809

Recommendation 91. Regulations preventing the user from holding the x-ray unit 3810

should not apply to equipment cleared by FDA that is designed to be hand-held. 3811

3812

10.1.4 CBCT Units 3813

3814

FDA’s performance standards specific to CT systems are included in 21 CFR 1020.33. Of 3815

particular importance to CBCT systems is the requirement to include quality assurance and 3816

control information (21 CFR 1020.33d). CT manufacturers are required to provide an image 3817

quality phantom, instructions for using the phantom, and a schedule for its use. 3818


162

3819

Considerable variability exists in the way state radiation control programs address CBCT 3820

systems, if at all. At the time of this writing, most states do not have specific requirements for 3821

dental CBCT systems and consider CBCT to be a form of dental radiography or panoramic 3822

radiography, although some states view CBCT to be a form of medical CT. The FDA classifies 3823

CBCT systems the same as conventional CT systems. The committee thinks that dental CBCT 3824

occupies a unique niche in the imaging world; CBCT should be considered neither a traditional 3825

dental equipment (intraoral, cephalometric or panoramic equipment) nor a conventional medical 3826

CT system. 3827

3828

The CRCPD Suggested State Regulations (SSR), Part F (Diagnostic and Interventional X-3829

Ray & Imaging Systems; http://crcpd.org/SSRCRs/default.aspx.), were revised in 2015 and 3830

include specific recommendations for CBCT units. At the time of writing, four states have 3831

adopted the SSR and others are considering it. 3832

3833

Recommendation 92. States shall develop and apply specific regulations for the dental 3834

uses of CBCT. 3835

3836

The radiation safety officer (RSO), which in a typical dental practice is the dentist, is 3837

responsible for remaining aware of current and potentially evolving changes in regulatory 3838

requirements for CBCT. The qualified expert may provide valuable help in this ongoing process. 3839

3840

Even in the complete absence of any specific state requirements for CBCT use, the RSO 3841

remains responsible for the safe use of radiation at the facility. Hence, it is prudent for the RSO 3842

to remain aware of the evolving state of the practice regarding state and local CBCT regulations 3843

as well as CBCT quality and safety practices, and to establish procedures in the dental clinic with 3844

these in mind. An experienced qualified expert can be a valuable resource in this important 3845

ongoing activity and may serve as the RSO. 3846

3847


163

Independent of any federal or state regulations, each dental practice employing CBCT 3848

should establish and maintain policies and procedures that address at least the following: 3849

3850

1. qualifications (including training and continuing education requirements) of individuals 3851

who may perform or read CBCT exams; 3852

2. personnel monitoring of occupational exposure, including periodic review by the 3853

radiation safety officer (RSO) or qualified expert; 3854

3. a CBCT quality assurance program, including both equipment related QC and clinically 3855

related QA activities; 3856

4. radiation safety and regulatory compliance program; 3857

5. standard CBCT protocols for common clinical indications; and 3858

6. periodic review of CBCT protocols by the dental practitioner and the qualified expert. 3859

3860

10.1.4.1 Advanced Diagnostic Imaging Accreditation. The Medicare Improvements for Patients 3861

and Providers Act of 2008 requires the accreditation of suppliers of the technical component of 3862

advanced diagnostic imaging services in order to obtain payment from the Centers for Medicare 3863

and Medicaid Services (CMS). For more information go to the CMS website (www.cms.gov) 3864

and search for “advanced diagnostic imaging accreditation.” 3865

3866

This provision of the act went into effect January 1, 2012, and includes dentists who obtain 3867

and bill Medicare for the technical component of CBCT examinations. The accreditation 3868

standard applies only to the suppliers of the images themselves, and not to the clinician’s 3869

interpretation of the images. The purpose of the accreditation is to ensure that quality images are 3870

produced in a safe and effective manner that benefits the patient. 3871

3872

Some states and private payers have adopted similar regulations. Clinicians and imaging 3873

facilities that utilized CBCT are advised to consult with local officials or representatives of the 3874

individual insurance company or payer for details specific to their location or situation. 3875

3876


164

10.2 Education and Training 3877

3878

NCRP Report No. 127 and Report No.134 (NCRP, 1998; 2000;) and ICRP Publication 3879

113 (ICRP, 2009) recommend that all dental personnel be appropriately trained in radiation 3880

protection. Basic familiarity with radiation protection can be expected in those who by education 3881

and certification are credentialed to expose radiographs, i.e., dentists, registered dental 3882

hygienists, certified dental assistants, and radiologic (or dental radiologic) technologists. 3883

Curricula for their education are subject to recommendations by various professional 3884

organizations and requirements of accrediting and credentialing agencies (IAC, 2015; ICRP, 3885

2009). These recommendations included credentialing of faculty and adequacy of resources and 3886

curricula for predoctoral and postdoctoral education, and required frequency of continuing 3887

education. Others have shown that dentists who are better informed in radiation science are more 3888

likely to adopt modern dose-optimization technology (Svenson et al., 1997b; 1998). 3889

3890

The ability of office personnel to understand and implement all of the recommendations 3891

in this Report cannot be assumed. Other personnel, e.g., secretaries, receptionists, laboratory 3892

technologists, who are not credentialed for performing radiographic procedures may be subjected 3893

to incidental exposure to radiation. These personnel are likely to have received little or no 3894

training or experience in radiation protection. 3895

3896

The required training may be provided by any combination of self-instruction (including 3897

reading), group instruction, online instruction, mentoring, or on-the-job training. Periodic 3898

evaluation of staff practices will determine the need, if any, for retraining. Essential topics to be 3899

covered in the training program include: 3900

3901

the ALARA principle; 3902

risks related to exposure to radiation and to other hazards in the workplace; 3903

dose limits; 3904

sources of exposure; 3905

basic protective measures; 3906

secure access to radiation equipment; 3907


165

warning signs, postings, labeling, and alarms; 3908

responsibility of each person; 3909

overall safety in the workplace; 3910

specific facility hazards; 3911

special requirements for women of reproductive age; 3912

regulatory and licensure requirements; and 3913

infection control. 3914

3915

This training may be expedited by the development and maintenance of a site-specific 3916

radiation protection manual. 3917

3918

Recommendation 93. Radiation safety training shall be provided to all dental staff and 3919

other personnel, including secretaries, receptionists, and laboratory technologists. This 3920

training shall be commensurate with the individual’s risk of exposure from ionizing 3921

radiation. 3922

3923

Recommendation 94. Every person who operates dental x-ray imaging equipment or 3924

supervises the use of such equipment shall have current training in the safe and 3925

efficacious use of such equipment. 3926

3927

When new imaging technology is introduced into a dental practice it is essential that the 3928

dentist and all operators be properly trained so as to be thoroughly familiar with the safe and 3929

efficient operation of the equipment. Continuing education resources are generally available to 3930

keep the dentist apprised of new developments. 3931

3932

Recommendation 95. The dentist should regularly participate in continuing education 3933

in all aspects of dental radiology, including radiation protection. 3934

3935

Recommendation 96. Opportunities should be provided for auxiliary personnel to 3936

obtain appropriate continuing education credits. 3937


166

3938

10.2.1 Digital Imaging 3939

3940

In addition to the basic education and training required for film-based imaging, the operator 3941

should be trained in the use of the radiographic imaging software that is used to acquire and 3942

manipulate the images. This training should be provided by the manufacturer or vendor of the 3943

equipment. 3944

3945

Furthermore, the operator should be educated and trained in the appropriate quality assurance 3946

and quality control protocols to assure the optimal performance of the film or digital imaging 3947

equipment components (Sections 5.2.4 and 5.2.6). 3948

3949

10.2.2 Hand-held Imaging Systems 3950

3951

Hand-held dental x-ray units are relatively new to the marketplace and require specific 3952

additional education for their safe and efficient operation. 3953

3954

10.2.2.1 Practitioner—Additional Safety Concerns. Practitioners should be aware of the potential 3955

for misuse of hand-held x-ray equipment and assure that the appropriate safeguards are in place. 3956

In addition, there is a potential for increased operator radiation exposure if the device is not used 3957

properly. 3958

3959

10.2.2.2 Operator Training. The hand-held x-ray equipment manufacturer must provide training 3960

materials for the operator. A DVD or online source could be used for operator training. 3961

3962

Operator training materials should include the basics of x-ray production and scatter (some 3963

operators such as dental assistants may not have had formal radiation safety training) and 3964

information on proper positioning. The positioning information should include the position of the 3965

patient, operator, location, and orientation of the hand-held device, and operator’s hand 3966

positioning on the device. This training should emphasize that the operator be positioned in a 3967

way that minimizes their exposure to backscattered radiation. In addition, the value of the x-ray 3968


167

shield which is an integral part of the unit should be emphasized, i.e., the shield must always be 3969

in place. 3970

3971

It is critical that operators follow the positioning instructions. Failure to follow proper 3972

positioning techniques can result in an increased exposure to backscattered radiation to the 3973

operator. 3974

3975

Recommendation 97. The manufacturer shall provide training pertaining to the safe 3976

operation of the hand held unit. 3977

3978

10.2.2.3 Qualified Expert—Required Information. The primary training issue for the qualified 3979

expert is the radiation safety of the hand-held x-ray unit. 3980

3981

Recommendation 98. The manufacturer of hand-held dental x-ray units shall provide 3982

information suitable for the qualified expert regarding radiation leakage, backscatter 3983

radiation, and the importance of the integral radiation shield. 3984

3985

10.2.3 CBCT Imaging Systems 3986

3987

CBCT units are an order of magnitude more sophisticated than any of the other dental 3988

imaging modalities and they require specific additional education for their safe and efficient 3989

operation. 3990

3991

In addition, the operator should be educated and trained in the appropriate quality control 3992

protocols to assure the optimal performance of the digital imaging equipment components 3993

(Sections 5.2.5). 3994

3995

10.2.3.1 Training for Practitioners 3996

3997

The complexity of CBCT image acquisition, and the subsequent multiplanar demonstration 3998

of patient anatomy, are far more complex than any imaging previously employed in dentistry. 3999


168

Thus, it is incumbent on practitioners to ensure that they receive proper training in the safe and 4000

effective use of this modality and provide opportunity for appropriate levels of training for the 4001

staff. 4002

4003

Recommendation 99. The predoctoral dental curricula shall include didactic and 4004

clinical education on physics of CBCT image production, artifacts that can lead to 4005

image degradation, indications, and limitations of CBCT in dental practice, and the 4006

effects of acquisition parameters on radiation dose. 4007

4008

Recommendation 100. Postdoctoral or clinical residency curricula shall expand upon 4009

the predoctoral education and include discipline-specific indications and limitations of 4010

CBCT imaging and the effects of acquisition parameters on radiation dose. 4011

4012

Recommendation 101. Dental practitioners who own CBCT units or use CBCT data 4013

sets in their clinical practice and who have not received CBCT education as part of 4014

their predoctoral, postdoctoral, or equivalent to predoctoral education shall acquire 4015

equivalent understanding of the basic radiation safety aspects of CBCT imaging and 4016

sufficient knowledge in the indications and limitations of CBCT imaging. 4017

4018

Recommendation 102. Dental personnel who operate CBCT units shall be adequately 4019

trained in the proper operation and safety of the units. They should demonstrate 4020

adequate knowledge of different protocols affecting the image quality and radiation 4021

dose to the patient. 4022

4023

Inadequate knowledge of the anatomy or not providing a proper interpretation of the image 4024

data set would negate and render moot any radiation protection benefits gained from safe and 4025

effective image acquisition. Thus, it is critical that the practitioner receive appropriate education 4026

and training in the interpretation of the anatomy as displayed on multiplanar and post-processed 4027

three-dimensional images. 4028

4029


169

10.2.3.2 Training for Operators. The operators of CBCT equipment are those licensed by the 4030

state in which they practice to operate dental radiographic equipment. Operators often select the 4031

equipment settings and perform image acquisition. In most states, operators of CBCT equipment 4032

are usually dental hygienists or dental assistants. 4033

4034

Recommendation 103. Prior to working with CBCT equipment, operators shall receive 4035

education on the basics of CBCT technology, the risks associated with radiological 4036

imaging, and training on the effective operation of CBCT equipment. This education 4037

must include principles of CBCT image formation, equipment settings and their impact 4038

on patient dose, and common artifacts associated with CBCT images. 4039

4040

Recommendation 104. All operators shall complete training on each individual CBCT 4041

system they will be using, as provided by the manufacturer. This device specific 4042

training must include patient positioning, the range of user selectable exam settings, 4043

and their effect on dose, protocol selection, image processing options, and periodic 4044

maintenance schedules. 4045

4046

10.2.3.3 Training for Qualified Experts. To be qualified for evaluation of CBCT equipment an 4047

individual must be a qualified expert with a minimum of 3 h CBCT training (available as online 4048

training) and have evaluated at least three CBCTs under the supervision of an experienced 4049

qualified expert. 4050

4051

Recommendation 105. A qualified expert shall have appropriate training and mentored 4052

experience in the evaluation of dental CBCT facilities prior to functioning 4053

independently. 4054

4055

10.2.3.4 Continuing Education for Practitioners, Operators, and Qualified Experts. CBCT 4056

technology is continually improving and practitioners, operators, and qualified experts must stay 4057

up-to-date. Manufacturers may provide software updates that substantially change the operation 4058

of the CBCT unit, which may require re-education and re-training of all parties. Similarly, 4059

hardware updates, while occurring less frequently, will also require additional education and 4060


170

training. It is the responsibility of the dentist to ensure that all office personnel are properly 4061

educated and trained in the safe and efficient operation of the equipment. 4062

4063

Recommendation 106. Every person who operates CBCT equipment, supervises the use 4064

of CBCT equipment or tests and evaluates the functions of CBCT equipment shall have 4065

ongoing continuing education in the safe and effective use of that equipment. 4066

4067


171

11. Summary and Conclusions 4068

4069

Oral and maxillofacial radiology encompasses a wide variety of techniques, ranging from 4070

traditional intraoral, panoramic and cephalometric imaging to more recently introduced digital, 4071

hand-held, and CBCT imaging. 4072

4073

While significant advances have been made in radiation dose reduction to patients and the 4074

public, there are still many examples of the utilization of equipment, supplies, and applications 4075

that are outdated and inappropriate. 4076

4077

Attention must be paid not only to how a radiographic image is captured but also to when the 4078

image should be captured. The dental clinician can minimize the exposure to the patient while 4079

maintaining diagnostic yield by utilizing the following: 4080

4081

1. selection criteria – have a good reason for acquiring any image; 4082

2. fastest available image receptor; 4083

3. optimized exposure technical factors; 4084

4. rectangular collimation with intraoral imaging; 4085

5. thyroid shielding for all intraoral images, and for other examinations as appropriate; 4086

6. smallest FOV and lowest dose acquisition parameters commensurate with the diagnostic 4087

task in CBCT; 4088

7. continuous quality control programs for equipment, techniques, film processing, and 4089

image receptors; and 4090

8. up-to-date training for all personnel. 4091

4092

Dentists who conduct their radiology practices in accordance with the requirements and 4093

suggestions in this Report can obtain maximum benefit to the oral health of their patients and 4094

minimum radiation exposure to patients, operators, and the public. All of the factors addressed in 4095

this Report are important and interrelated; quality practice dictates that no shall statement be 4096

neglected and that should statements be incorporated whenever possible. The technical factors, 4097

including office design and shielding, equipment design, clinical techniques, image receptors, 4098


172

darkroom procedures, quality control, and quality assurance are essential. However, the 4099

professional skill and judgment of the dentist in prescribing radiologic examinations and 4100

interpreting the results are paramount. 4101

4102

While radiogenic harm due to most very low-dose dental x-ray examinations may not be 4103

unequivocally demonstrable, recent epidemiological studies have shown an association between 4104

low-dose exposures associated with CBCT (doses on the order of those found with MDCT) and 4105

increased cancer risk across the population (Appendix I). 4106

4107

Given the uncertainty regarding the estimated risk from low-doses such as those found in 4108

diagnostic imaging (NCRP, 2010b; UNSCEAR, 2012), there is disagreement about the 4109

application of the risk estimates to policy development and radiation protection issues (AAPM, 4110

2012; HPS, 2016). However, given the large number of dental images taken annually, the 4111

possibility that the risks are real, especially for CBCT imaging, demands that they be taken 4112

seriously in the interest of patient, staff, and public safety. 4113

4114


173

Appendix A 4115

4116

Quality Control for Film Processing 4117

4118

Radiation exposure to the patient, operator, and public can be reduced by minimizing the 4119

need for repeat exposures because of inadequate image quality (NRPB, 2001). In addition, the 4120

chemical solutions must be maintained at the proper activity level. As the chemicals are depleted 4121

or oxidized, the films will be lighter resulting in an increased exposure times and higher doses to 4122

the patients and staff. Film processing chemistry and procedures, image receptor performance 4123

characteristics, and darkroom integrity must be evaluated at appropriate intervals. These routine 4124

quality control procedures can be performed by dental office staff. 4125

4126

A.1 Five Basic Rules for Film Processing 4127

4128

1. Films should be processed at the time and temperature specified by the film 4129

manufacturer. 4130

Film processing is a chemical reaction requiring accurate control of the processing time 4131

and temperature. 4132

An important part of processor quality control is maintaining the appropriate 4133

developer and fixer activity. This is accomplished through replenishing of the solutions in 4134

the developer and fixer tanks. 4135

2. The developer and fixer must be replenished regularly to maintain diagnostic image 4136

quality, and minimize patient dose. 4137

Eight ounces of replenisher should be added every day, assuming 30 intraoral or five 4138

panoramic films. An additional eight ounces of replenisher should be added per day for 4139

each additional 30 intraoral or five panoramic films processed (White and Pharoah, 4140

2014). Manufacturer’s instructions should be followed where applicable. 4141

3. Never top off the chemical tanks with water. 4142

This dilutes the chemicals, reduces image quality, and could lead to an increase in patient 4143

radiation dose. 4144

4145


174

4. Developer and fixer solutions should be changed every two weeks. 4146

Over time the solutions tend to collect bits of debris from the film, become depleted, and 4147

oxidize. Consequently, it is necessary to drain the solutions, clean the tanks, and fill the 4148

tanks with fresh chemicals. 4149

5. The water in the wash tank should be changed daily for up to 30 films developed per 4150

day. For higher volumes, the water should be changed after every 30 films. (Some 4151

processors have water flowing through the wash tanks—the water in these processors 4152

does not have to be changed due to the continuous flow of fresh water.) 4153

Improper washing of films will result in premature fading and staining of the images.3 4154

4155

A.2 Quality Control 4156

4157

A.2.1 Sensitometry and Densitometry 4158

4159

The most sensitive and rigorous method of quality control requires the use of a sensitometer, 4160

a precise optical device to expose a film to produce a defined pattern of optical densities in the 4161

processed film. These densities are then measured with a densitometer, and compared to the 4162

densities of a similarly exposed film previously processed in fresh solutions under ideal 4163

conditions. These values are placed on a control chart. Any change beyond pre-specified limits 4164

indicates a problem with processing which could be a result of changes in development time or 4165

temperature, or due to depleted or contaminated solutions. This method requires additional 4166

equipment but only a few minutes of operator time to execute. It is highly recommended for the 4167

busy facility, but simpler, less costly methods may be adequate for average dental offices. 4168

4169

A.2.2 Dental Radiographic Quality Control 4170

4171

Two devices are available from most dental supply companies for simple quality control of 4172

film processors—a dental radiographic quality control device (DRQCD) and an aluminum step 4173

wedge. In addition to daily QC, the DRQCD assists in selecting appropriate exposure time to 4174

3 Gray, JE (2015). Personal Communication. (DIQUAD, LLC, Steger Illinois)


175

assure that patients are receiving an appropriate radiation dose. A third test device can be 4175

constructed from the leaf foils in dental film packets. 4176

4177

A.2.3.1 Dental Radiographic Quality Control Device. This device consists of a small sheet of 4178

copper and a comparison optical density step wedge. For quality control, an exposure is made 4179

with a film packet under the copper, the film is processed, and then compared to the step wedge. 4180

If the film density changes by more than one step then a change in photographic processing has 4181

occurred and it will be necessary to determine and correct the cause. 4182

4183

This device is also useful in establishing the appropriate exposure time for dental 4184

radiographs. In this case, a film packet is exposed under the copper plate and compared to the 4185

optical density step wedge. The appropriate exposure time results in the film density matching 4186

the middle step of the step wedge. 4187

4188

A.2.3.2 Aluminum Step Wedge. An aluminum step wedge with 1 mm steps can be used for film 4189

processor quality control. A film packet is exposure under the aluminum step wedge and the film 4190

is processed with fresh film processing chemistry. This film becomes the comparison or baseline 4191

film. For daily quality control purposes, the procedure is repeated with the resultant film being 4192

compared to the baseline film. If the steps of the baseline film and the recently exposed film are 4193

not similar then it will be necessary to determine and correct the cause. 4194

4195

A.2.3.3 Lead Foil Step Wedge. A step wedge can be made of multiple layers of the lead foil from 4196

dental film packets (Valachovic et al., 1981). Overall size of the stepwedge should be similar to 4197

that of a standard intraoral film. It is made to resemble stairs. There should be at least six steps. 4198

4199

The lead foil step wedge is used in the same manner as the aluminum step wedge. 4200

4201

A.2.3.4 Reference Film. Use of a properly exposed and processed intraoral film as a reference 4202

has been proposed as another method of quality assurance (Valachovic et al., 1981). When using 4203

this method, a high-quality film is attached to a corner of the view box. Subsequent clinical films 4204

can then be compared with this reference film. This method is not as sensitive or reliable as the 4205


176

use of the DRQCD device, or a stepwedge, and is not recommended for routine use. In rare 4206

circumstances it may be used as a stopgap measure, usually in facilities with very low 4207

radiographic workload (fewer than 10 intraoral films per week). 4208

4209


177

Appendix B 4210

4211

Quality Control for Digital Imaging Systems 4212

4213

B.1 Quality Control of Digital Intraoral Systems 4214

4215

Quality control testing of digital systems requires: 4216

4217

1. computer display adjusted to display a high-quality radiographic image and viewed under 4218

optimal conditions; 4219

2. suitable phantom or test object to be used for the assessment of image quality; 4220

3. procedure providing verification that the radiographic technique being used yields the 4221

maximum diagnostic information at an acceptable level of dose (optimization); 4222

4. exposure of a baseline image to serve as a reference for subsequent images; 4223

5. exposure of follow-up radiographs at regular intervals; and 4224

6. system of record keeping for purposes of documentation. 4225

4226

B.1.1 The Display 4227

4228

Since digital radiographs are viewed on a computer display, it should be verified that the 4229

display is viewed under optimal conditions. The display should be tested to verify that it is 4230

functioning optimally and the brightness and contrast are properly adjusted. 4231

4232

Digital radiographs should be viewed with the center of the display positioned slightly below 4233

eye level. Subdued lighting should be used and every effort should be made to eliminate 4234

reflections from extraneous sources of light such as room lights or view boxes. 4235

4236

The display should be checked periodically using the Society for Motion Picture and 4237

Television Engineers (SMPTE) Medical Diagnostic Imaging Test Pattern or the equivalent. The 4238

overall image should be inspected to insure the absence of gross artifacts such as blurring or 4239

bleeding of bright display areas into dark areas. All the provided gray levels should be visible 4240


178

and both the 5 % and the 95 % areas should be seen as distinct from the surrounding 0 % and 4241

100 % areas. Brightness and contrast should be adjusted until these conditions are met (Gray, 4242

1992; Gray et al., 1985). 4243

4244

B.1.2 Quality Control Phantoms 4245

4246

A thorough evaluation of image quality requires a phantom containing suitable test objects 4247

for assessing low-contrast detectability and spatial resolution as well as a step wedge or some 4248

other suitable object covering the relevant range of radiographic attenuation (Mah, 2011; Udupa, 4249

2013). The phantom should be exposed using the source-to-image distance used clinically and 4250

the test objects should be positioned at the same distance from the x-ray source and image 4251

receptor as the relevant anatomy. 4252

4253

B.1.3 Baseline Exposure Assessment 4254

4255

The object of the original baseline assessment is to evaluate the technique being used for 4256

routine exposures and to improve on it, if possible. The objective is to determine the lowest 4257

exposure at which the greatest number of low-contrast details are visualized and the highest 4258

resolution is obtained while continuing to display the full range of clinically relevant gray levels. 4259

Established guidelines for Diagnostic Reference Level and Achievable Dose set limits on the 4260

exposures that should be used, even when the image receptor is capable of producing high 4261

quality images at levels of radiation exposure exceeding these guidelines. NCRP 172 establishes 4262

the DRL and AD for intraoral imaging at 1.6 and 1.2 mGy, respectively (NCRP, 2012b). 4263

4264

A starting point for baseline exposure assessment can be obtained from Table 6.1 of this 4265

report. This phase is a process of trial and error but it is a necessary step before quality control 4266

monitoring begins. 4267

4268


179

B.1.4 Baseline Image 4269

4270

Once the baseline exposure time is established, the test image should be saved for future 4271

reference. Any information extracted from the image, as well as the geometry and exposure 4272

factors should be recorded. 4273

4274

A new baseline exposure assessment should be performed and a new baseline image acquired 4275

if any components of the x-ray equipment are altered, repaired, or adjusted, or if any changes are 4276

made to the hardware or software used for image capture. 4277

4278

B.1.5 Follow-up Images 4279

4280

Following the baseline assessment, the phantom should be radiographed at regular intervals 4281

using the standard exposure geometry and baseline exposure factors. The image should be 4282

compared to the baseline image. A significant deviation from the baseline indicates that a change 4283

has occurred that should be investigated. Corrective action should be taken as needed. The test 4284

should also be performed if damage to the image receptor is suspected after an event such as 4285

dropping the image receptor, biting the image receptor, running over the cord with chairs or 4286

equipment, snagging the electrical cord, etc. 4287

4288

B.1.6 Record Keeping 4289

4290

A permanent record should be kept of baseline and follow-up data. The date of the test and 4291

the name of the person performing the test procedure should be included. The nominal 4292

kilovoltage and milliamperage as well as the baseline exposure time should be noted as well as 4293

the technical factors that are measured. A separate log should be maintained for every x-ray unit 4294

and image receptor combination and, in the case of a practice using PSP plates, every x-ray unit 4295

and scanner combination. The following is a quality control record containing the essential 4296

elements discussed above: 4297

4298


180

Quality Control Record 4299

4300

Image receptor (Manufacturer, Model, Serial #) ________________________________ 4301

4302

X-ray Machine (Manufacturer, Model, Serial #) _________________________ 4303

4304

kVp ___________ 4305

4306

mA ___________ 4307

4308

Baseline Quality Control Exposure. ________ sec 4309

4310

Baseline

Date

Name Steps Line-Pairs Top Row

of Contrast

Holes

Second Row

of Contrast

Holes

4311

4312

Date Name Steps Line-Pairs Top Row

Of Contrast

Holes

Second Row

of Contrast

Holes

4313

4314


181

Appendix C 4315

4316

Historical Aspects of Digital Imaging 4317

4318

The benefits to the practice of dentistry from capturing “skiagrams”, as x-ray images were 4319

called at the time, were realized soon after the discovery of x rays. During the following 100 y 4320

substantial technological improvements advanced most aspects of radiological imaging; 4321

however, the film based format of radiographic image capture, display, and archiving remained 4322

largely unchanged throughout most of the 20th century. Xeroradiography, with its capture of 4323

image detail, was a somewhat viable alternative to film based methods; however, initial 4324

investment cost, unique equipment requirements, and perhaps a reluctance of radiologists to 4325

interpret a blue radiographic image on dull white paper likely played a role in the mainstay of 4326

radiographic film into the 21st century. Digital imaging has been a facet of general radiological 4327

practice since the 1980s, first with computed radiography (using PSP technology) and later with 4328

direct digital radiography in various forms (although one can argue that computed tomography 4329

was actually the first digital oriented radiological imaging procedure based on the digital 4330

acquisition and computational nature of this modality). Recent technological advances have 4331

allowed x-ray imaging in the dental practice to quickly embrace digital technology. 4332

4333

Digital based x-ray imaging for dental applications has been a part of clinical practice since 4334

the early 1990s. There are likely a number of reasons for the increase in the number of dental 4335

practices that have switched to digital imaging for intraoral and extraoral modalities. A recent 4336

study found that 87 % (n = 81) of facilities in the United States are now using digital imaging for 4337

intraoral examinations (Farris and Spelic, 2015). A second study in the United States found that 4338

85.8 % (n = 1,312) for facilities are using digital intraoral imaging.4 This same study found that 4339

the percentage of facilities using digital intraoral imaging in the United States was increasing by 4340

~8 % y–1 from 2010 through 2015. Another study conducted recently of dental practices in New 4341

Zealand found that the majority of dental practices had implemented digital x-ray imaging, and 4342

not surprisingly, younger practitioners were more likely to be using digital imaging. Among the 4343

4 Gray, J.E. (2015) Personal communication (DIQUAD, LLC, Steger, Illinois).


182

reasons that dental practices preferred digital imaging were the chemical free imaging process, 4344

lower dose that digital imaging could offer, the rapid availability of the image, and the ability to 4345

digitally archive patient imaging records. Practices surveyed that were still using film tended to 4346

be satisfied with the modality and felt that switching to digital imaging would be costly. One 4347

survey finding that supports the assumption that digital imaging is a more timely modality than 4348

film was the finding that practices using digital imaging tended on average to acquire more 4349

images per day. 4350

4351

Digital imaging first became available for dentistry in the late 1980s when technology was 4352

sufficient to allow the digital image capture devices to be packaged suitably for dental 4353

applications. In 1987 the French company Trophy introduced their product, RadioVisioGraphy, 4354

as a digital based tool for dental x-ray imaging. Although early digital technologies were not 4355

capable of the high spatial detail that traditional film provides, these technologies continued to 4356

mature, and some device manufacturers now offer a wireless means of image capture. One study 4357

demonstrated that 2D imaging with digital technology for bone lesions provided better clinical 4358

performance than traditional film imaging. Today the digital technologies for oral radiography 4359

fall into two broad categories of image receptors: solid state (predominantly CCD or CMOS 4360

based) devices and photostimulable storage phosphor (PSP) technology. 4361

4362

Although the spatial resolution of digital systems may be inferior to film, the contrast 4363

resolution, i.e., the ability to see small density differences, is better for digital imaging (Figure 4364

C.1). 4365

4366

Similar to imaging equipment available for general radiological imaging, digital based x-ray 4367

equipment generally is either PSP based or solid state receptor based. While the fundamental 4368

technologies of these two equipment types are different, there are a number of common benefits 4369

that these two systems offer. 4370

4371


183

4372

4373

4374

4375

4376

4377

4378

Fig. C.1. (Left) film image; (right) digital image. Low contrast area on the digital image (red 4379

arrow) is not visible on the film image. Low contrast area consists of 1 mm aluminum disk with 4380

a circular hole in two layers of tape. 4381

4382


184

4383

One benefit to embracing digital imaging in clinical practice is the elimination of chemical 4384

film processing. Film processing can be a time consuming and laborious aspect of x-ray imaging 4385

to maintain at an acceptable level of quality. A survey of dental facilities in 2014 4386

(http://imagegently.org/) showed broad ranges for clinical image quality including film 4387

background optical density, film contrast, and the quality of film processing. Poor film 4388

processing (generally considered to be the under-development of film) can affect clinical image 4389

quality and also leads to higher patient doses to compensate. The same 2014 survey found that 4390

even for those surveyed sites using D-speed film, patient exposures varied broadly, with the first 4391

and third quartiles for patient exposure differing by a factor of 2.3 and 45 % failed an acceptance 4392

criteria of 2.6 mGy, i.e., exceeded this radiation exposure level. (The range of exposures for D-4393

speed film was from 50 to 800 mR.) Although arguably PSP based systems still require digital 4394

image “processing”, the general need to provide a darkroom environment for handling film and 4395

maintaining a chemical based processing environment are eliminated. Digital images can be 4396

easily and quickly transferred to other clinical practices as DICOM standard formatted images 4397

using the Internet. 4398

4399

Likely one of the most substantial benefits of capturing radiographs using digital technology 4400

is the ability to conduct digital image processing. Although (intraoral) dental film offers 4401

tremendous spatial resolution of 20 c mm–1 or greater, digital image processing can provide a 4402

system of tools that offer the clinician the ability to manipulate the image to suit the clinical task 4403

at hand. In general the near instant availability of digital images provides a level of convenience 4404

for both the dental practitioner and the patient. However, when considering a migration to digital 4405

based imaging, clinical considerations are helpful in determining the particular system 4406

requirements that are suitable for the practice, such as the routine imaging of challenging 4407

anatomical presentations, and the workload for pediatric exams. 4408

4409


185

Appendix D 4410

4411

Shielding Design for Dental Facilities 4412

4413

NCRP Report No. 147 entitled, Structural Shielding Design for Medical X-Ray Imaging 4414

Facilities (NCRP, 2004), discusses shielding design for x-ray sources with operating potentials in 4415

the range from 25 to 150 kVp. Techniques used for calculating shielding barriers for diagnostic 4416

medical x-rays also have been discussed in the literature (Dixon and Simpkin, 1998; Simpkin 4417

and Dixon, 1998). Since dental radiography uses equipment similar in radiation quality to that 4418

used in diagnostic medical x-ray facilities, this appendix will provide information regarding the 4419

unique features of dental radiography equipment so that the qualified expert will be able to 4420

design shielding using the methodology described in NCRP Report No. 147 (NCRP, 2004). 4421

4422

Conventional building materials in partitions, floors, and ceilings may provide adequate 4423

radiation shielding for dental installations. However, assuming that conventional or pre-existing 4424

barriers provide sufficient shielding without a qualified expert performing a careful review of the 4425

required shielding based on current equipment, current workloads, and occupancy of surrounding 4426

areas can lead to exceeding permissible levels of radiation exposure in public and controlled 4427

areas, and therefore is ill advised. 4428

4429

Implementing several of the recommendations of this report (e.g., eliminating the use of D-4430

speed film, using digital imaging, and using rectangular collimators for intraoral imaging) may 4431

decrease the total amount of amount scattered radiation produced for each intraoral radiographic 4432

image. Diagnostic quality images may be produced using a lower radiation exposure for each 4433

image with photostimulable phosphor or direct digital imaging receptors instead of film for 4434

intraoral imaging. Whether converting to F-speed film or digital image receptors, where such 4435

technique factor reductions are implemented clinically, the attenuation requirements for 4436

structural shielding will be proportionally reduced if the total number of exams remains 4437

unchanged. 4438

4439


186

Despite the common misconception that CBCT systems are “nothing more than fancy 4440

panoramic x-ray systems and no shielding is needed,” scattered radiation from CBCT is 4441

substantially higher than from panoramic x-ray systems, typically by approximately a factor of 4442

10 times or more. Compared with panoramic x-ray installations, the substantially higher 4443

scattered radiation levels in CBCT installations require significantly greater shielding to maintain 4444

radiation exposures to nearby persons ALARA. Because CBCT systems are often replace 4445

existing panoramic systems, it is especially critical to have a qualified expert assess the adequacy 4446

of shielding prior to the CBCT installation. While some panoramic x-ray systems can be 4447

operated in a corridor or alcove without exceeding permissible radiation levels to nearby 4448

individuals, CBCT systems installed in a corridor or alcove will often expose nearby persons to 4449

doses that exceed permissible levels. Typically, CBCT systems should be installed in an enclosed 4450

room, with the thickness of shielding materials determined by a qualified expert. Figure D.1 4451

depicts typical configurations for CBCT systems 4452

4453

D.1 General Shielding Principles 4454

4455

In dental radiology, the beam energy is determined by the demands of radiographic contrast, 4456

but typically ranges from 60 to 70 kVp for intraoral dental radiography. Recently manufactured 4457

dental intraoral radiography units do not exceed 80 kVp. [Most intraoral dental units utilize fixed 4458

kilovoltage (70 kVp) and fixed milliamperage.] Panoramic x-ray units operate from 70 to 4459

100 kVp. Cephalometric systems are similar to standard radiographic systems and operate from 4460

60 to 90 kVp. Cone beam computed tomography (CBCT) systems generate significant higher 4461

levels of scattered radiation since the entire image receptor is irradiated continuously during the 4462

exposure, as opposed to irradiation from a small slit aperture in panoramic imaging. CBCT 4463

systems operate from 70 to 120 kVp. 4464

4465

4466


187

4467

4468

4469

4470

4471

4472

4473

4474

4475

Fig. D.1. Diagram illustrating primary barrier B, protecting person at C from useful beam at 4476

a distance dP from dental x-ray source A. 4477

4478


188

D.2 Shielding for Primary and Secondary Radiation 4479

4480

The primary beam is the intense, collimated radiation field that emanates from the x-ray tube 4481

focal spot and tube port, and is incident upon the patient. Figure D.1 illustrates a primary 4482

protective barrier B in the useful beam that attenuates the beam before it reaches a person located 4483

at C. In most situations, the primary beam also is attenuated by the patient before impinging on 4484

the primary barrier. The theory of shielding primary radiation from diagnostic x-ray facilities has 4485

been discussed by Dixon and Simpkin (1998) and in NCRP Report No. 147 (NCRP, 2004a). 4486

4487

Experimental evidence using the Rando phantom (de Haan and van Aken,1990) suggests that 4488

the intensity of the primary beam exiting the patient may be approximately twice that of the 4489

scattered radiation (Figure D.2). However, additional attenuation from the image receptor and 4490

bony anatomy of the human head, coupled with the relatively small beam size and logistical 4491

aspects of intraoral imaging5 serve to mitigate the primary beam effect. In addition, Figure 7.2 4492

indicates that the radiation exposure exiting the patient is ~0.5 to 1.0 mR for D-speed intraoral x-4493

ray film. (The image in Figure 7.2 was produced using a 400-speed screen-film system which 4494

requires ~0.5 mR to produce an optical density of 1.00 on the film.) Entrance exposures are even 4495

lower for digital imaging systems so the exit exposure from the patient would be approximately 4496

one-quarter to one-half of that with D-speed film. [The recent NEXT survey found that 87 % of 4497

facilities in the United States are now using digital imaging (Farris and Spelic, 2015)]. 4498

4499

Neglecting the primary beam in shielding calculations for dental facilities will not affect the 4500

calculated barrier thicknesses or resultant exposures to persons who occupy areas nearby the 4501

intraoral radiographic installation. 4502

4503

Consequently, the NCRP recommends that primary radiation can be neglected in dental 4504

imaging. Only scattered radiation must be considered in shielding design for dental facilities. 4505

4506

5 Unlike conventional radiology, the primary beam in dental imaging is placed at different locations and angles for intraoral radiography for each image. This results in the radiation being at projected at multiple locations on barrier B in Figure D.1.


189

Proposed CBCT

4507

4508

a. 4509

4510

4511

4512

4513

4514

4515

4516

4517

4518

4519

4520

4521

4522

4523

4524

4525

4526

4527

b. 4528

4529

Proposed CBCT


190

4530

4531

c. 4532

4533

4534

4535

4536

4537

4538

4539

4540

4541

4542

4543

Fig. D.2. (a) Initially proposed installation of CBCT system, to replace existing panoramic 4544

unit. This installation provides suboptimal radiation protection and would require administrative 4545

occupancy restrictions in the hallway during x-ray exposure. (b, c) Options for preferred 4546

installation of CBCT system in a different area of the suite, providing significant improvement in 4547

radiation protection and eliminating the need for administrative controls on hallway occupancy 4548

during x-ray exposure needed for the initially proposed installation. 4549

4550


191

4551

D.3 Shielding Principles 4552

4553

Shielding design goals for dental x-ray sources are practical values that result in the 4554

respective limits for effective dose in a year to workers and the public not being exceeded, when 4555

combined with conservatively safe assumptions in the structural shielding design calculations 4556

(NCRP, 2004). The shielding design goal is expressed as a weekly value, consistent with 4557

workload and occupancy factor data 4558

4559

D.4 Occupancy Factors, Use Factors, and Workloads 4560

4561

D.4.1 Occupancy Factors 4562

4563

Suggested occupancy factors are provided in Table D.1. 4564

4565

D.4.2 Use Factors 4566

4567

Since one need consider only scattered radiation for shielding design in dental radiography, 4568

the use factor is not applicable. 4569

4570

D.4.3 Workloads 4571

4572

Suggested workloads for intraoral (IO) imaging are provided in Table D.2. 4573

4574

Suggest workloads for panoramic, cephalometric, and CBCT imaging are given in Table D.3 4575

(see also MacDonald et al., 1983; Reid and MacDonald, 1984; Reid et al., 1993). 4576

4577

4578


192

TABLE D.1—Suggested occupancy factorsa (for use as a guide in planning shielding where 4579

other occupancy data are not available) (NCRP, 2004). 4580

4581

Location Occupancy

Factor (T)

Administrative or clerical offices; laboratories, pharmacies and other work areas

fully occupied by an individual; receptionist area, attended waiting rooms,

children’s indoor play areas, adjacent x-ray rooms, reading area, nurse’s stations, x-

ray control rooms

1

Patient examination and treatment rooms 1/2

Corridors, patient rooms, employee lounges, staff toilets 1/5

Public toilets, unattended vending areas, storage rooms, outer areas with seating,

unattended waiting rooms, patient holding areas 1/20

Outdoor areas with only transient pedestrian or vehicular traffic, unattended parking

lots, vehicular drop off areas (unattended), attics, stairways, unattended elevators,

janitor’s closets

1/40

aWhen using a low occupancy factor for a room immediately adjacent to an x-ray room, care should

be taken to also consider the areas further removed from the x-ray room that may have significantly higher

occupancy factors and may, therefore, be more important in shielding design despite the larger distances

involved.


193

TABLE D.2—Suggested workloads for intraoral (IO) units. 4582

Type of Unit Images w-1 kVp mAs per

Image

Film or Image Receptor

Speed

Low Volume IO 25 70 4.5 F or Digital

Medium Volume IO 100 70 4.5 F or Digital

High Volume IO 200 70 4.5 F or Digital

4583

4584


194

TABLE D.3—Suggested workloads and technique factors for cephalometric, panoramic, and 4585

CBCT examinations. 4586

Panoramic Cephalometric CBCT

Low volume facility

(exams w-1) <15 <10 <10

Medium volume facility

(exams w-1) 15 – 30 10 – 20 10 – 20

High volume facility

(exams w-1) >30 >20 >20

kVp 85 – 100 80 – 90 90 – 120

mAs per image for 400-speed

film or digital image receptor 50 – 1006 7 – 25 60 – 1607

4587

6 Slot beam. Depends on pulsed or nonpulsed beam, pulse width, and patient size. 7 Depends on pulsed or nonpulsed beam, pulse width, field of view, resolution, and patient size.


195

D.5 Summary 4588

4589

Shielding in dental radiography facilities is not as complex as for medical facilities. 4590

However, sufficient consideration must be given to future workloads to assure that 4591

shielding is adequate. Particularly for new construction and typical circumstances, 4592

appropriate shielding adds little to the cost of construction. Prior to facility operation, a 4593

performance assessment by a qualified expert is necessary to confirm that occupational and 4594

public effective dose limits will not be exceeded. The recommendations in this Report are 4595

to be applied to upgraded or new shielding designs, but not necessarily to existing barriers 4596

that otherwise met prior requirements. 4597

4598


196

Appendix E 4599

4600

Dosimetry, Intraoral and Panoramic Imaging 4601

4602

E.1 Patient Dosimetry 4603

4604

Dental radiographic procedures are very common but the associated x-ray doses are 4605

quite low. Application of the ALARA principle to reduction of these doses is justified. For 4606

intraoral radiography, changing from D- to E-F-speed film or to digital image receptors 4607

results in dose reduction by factors of at least two. Introduction of rectangular collimation 4608

to replace the 7-cm round beam reduces dose by factors of four to five. Both of these are 4609

accomplished at little or no cost, and together may result in ten-fold reductions in effective 4610

doses. 4611

4612

This Section provides the dentist with data, e.g., Tables E.1 and E.2, on the magnitude 4613

of effective doses from typical dental x-ray procedures. General statements are given in 4614

this Section that can be used to inform the patient about the radiation doses from dental x-4615

ray procedures and the nature of risk associated with these doses. Additional background 4616

on radiation risk assessment is found in Appendix I. Dentists are encouraged to use this 4617

information to educate their patients as opportunity provides. 4618

4619

Tables E.1 and E.2 are taken from literature reporting 2007 ICRP calculations of 4620

effective dose. 4621

4622

Figure E.1 shows the distribution of absorbed radiation doses throughout structures in 4623

the maxillofacial region following a full mouth series (Gibbs et al., 1987). While this is an 4624

old figure using D-speed film, it is the only such figure in the literature. The doses for 4625

E-F-speed film or digital imaging would be approximately one-half of the printed values. 4626

4627

4628


197

TABLE E.1— Effective dose of dental panoramic radiography units. 4629

Unit Manufacturer kVp mA Time

(s)

Effective

Dose

(µSv)

Reference

Veraviewepocs 3De Morita 78 10 7.4 11 Al-Okshi (2013)

ProMax 3D Planmeca 66 9 16 8 Al-Okshi (2013)

ProMax Planmeca 74 12 16 14 Al-Okshi (2013)

OP200 Instrumentarium 66 10 17.6 11 Han (2013)

Orthophos CD Sirona 71 15 13.9 14 Han (2013)

Orthophos XG plus Sirona 69 15 14.1 19 Han (2013)

ProMax Planmeca 66 12 16 26 Grünheid T (2012)

OP100 Instrumentarium 73 12 17.6 22 Ludlow (2011)

Orthophos XG Sirona 64 8 14.1 14 Ludlow (2011)

ProMax Planmeca 68 13 16 24 Ludlow (2011)

Kodak - 9000 Carestream 70 10 14.3 15 Ludlow (2011)

SCANORA 3D Soredex 73 6.3 15 13 Ludlow (2011)

OP 200 VT Instrumentarium 66 8.9 16.8 15 Ludlow (2011)

Average 70 11 15 16

Standard deviation 4.1 2.6 2.7 5.4


198

TABLE E.2— Effective Doses for plain dental radiographic views. 4630

Technique Effective Dose

(µSv)

FMX with D Speed film and Round Cone† 388

FMX with PSP or F-Speed film and Round Cone 171

FMX with PSP or F-Speed film and Rectangular Collimation 35

BWs with PSP or F-Speed film and Rectangular Collimation 5

PA Cephalometric - PSP 5.1

Lateral Cephalometric - PSP 5.6

4631

4632


199

4633

4634

4635

4636

4637

4638

4639

4640

4641

4642

4643

4644

4645

Fig. E.1. Isodose curves calculated for full-mouth intraoral examinations obtained at 4646

80 kVp using optimum exposures for D-speed film. Lines without numeric annotations 4647

indicate skin surface and internal hard tissue surfaces. Numeric annotations indicate 4648

absorbed dose in microgray (1,000 µGy = 1 mGy). For example, the tissues contained 4649

within the contour labeled 5,000 receive an absorbed dose of at least 5 mGy (5,000 µGy). 4650

(A) Transverse section through the occlusal plane, 7 cm round beams. Note that the teeth 4651

receive absorbed doses of at least 12 mGy, and all tissues anterior to the cervical spine 4652

receive at least 5 mGy. (B) Same plane with rectangular collimation. Areas contained 4653

within each isodose contour are smaller than in A. Absorbed dose is generally confined to 4654

the facial area, with posterior regions receiving absorbed doses no >1 mGy (Gibbs et al., 4655

1987). 4656

4657


200

E.2 Operator Dosimetry 4658

4659

Figure E.2 provides the supporting evidence for recommendation that the operator 4660

exposing intraoral images should stand at an angle of 90 to 135 degrees from the central 4661

ray (Figure 4.1). 4662

4663


201

4664

4665

4666

4667

4668

4669

4670

4671

4672

4673

4674

4675

4676

Fig. E.2. Operator exposure as a function of position in a room relative to patient and 4677

primary beam for intraoral imaging. View from above for a left molar bitewing. The heavy 4678

line in the polar coordinate plot indicates dose by its distance from the center of the plot. 4679

Maximum dose is in the exit beam on the side of the patient opposite the x-ray tube. The 4680

recommended positions for minimum exposures (crosses) are at 45 degrees from the exit 4681

beam. Note that most scattered radiation is backward toward the x-ray tube (de Haan and 4682

van Aken, 1990). 4683

4684


202

Appendix F 4685

4686

Dosimetry for Multidetector-Multislice Imaging of Dentomaxillofacial Areas 4687

4688

TABLE F.1— Effective dose from MDCT scanning of dental and maxillofacial areas. 4689

Unit Exam kVp mA Time

(s)

Voxel

(mm)

Height

(cm)

Effective

Dose

(µSv)

Somatom Emotion 6 - low

dose (Jeong, 2012) Mandible 110 3.1 16 0.6 5 199

Somatom Sensation 10

(Jeong, 2012) Mandible 120 23.8 8.4 0.6 5 426

Somatom VolumeZoom 4

(Loubele, 2009) Mandible 120 90 15 0.75 7 494



Mx8000 IDT


Somatom 64 - low dose

(Ludlow, 2008) Jaws 120 48 – 64 1 0.6 12 534

Somatom 64

(Ludlow, 2008) Jaws 120 90 1 0.6 12 860

Somatom VolumeZoom 4

(Loubele, 2009) Head 120 90 44 0.75 23 1,110


(Loubele, 2009) Head 120 90 29 0.75 23 995

Mx8000 IDT

(Loubele, 2009) Head 120 140 30 0.75 23 1,160

4690

4691


203

TABLE F.2—Summary of effective doses from MDCT scanning of dental and maxillofacial 4692

areas. 4693

MDCT - Isotropic Voxels

Average

Effective Dose

(µSv)

Low

(µSv)

High

(µSv)

Mandible 427 199 541

Jaws 697 534 860

Head 1,088 995 1,160

4694


204

Appendix G 4695

4696

Dosimetry for Dental Cone Beam CT Imaging 4697

4698

The effective dose data in Tables G1 through G6 as well as the salivary gland, thyroid 4699

gland, and brain components of effective dose (recorded without weighting as equivalent dose) 4700

were assessed using one-way ANOVA (Tables G7 to G11), followed by pairwise comparisons 4701

when appropriate (Tukey HSD). 4702

4703

4704


205

TABLE G.1— Effective doses for standard or default exposures for large FOV CBCT units 4705

(>15 cm height). 4706

Unit Name (reference)

Manufacturer

FOV Size

H ・ Wa

(cm)

kVp mAs Effective

Dose (µSv)

3D eXam (Rottke, 2013)

Imaging Sciences 17 ・ 23 120 18.5 78

3D eXam (Schilling, 2013)


CB Mercuray (Librizzi, 2011; Jadu, 2010)

Hitachi 19 ・ 19b 120 150 924c

CB Mercuray (Ludlow, 2008; Jadu 2010)

Hitachi 19 ・ 19b 100 100 518c

CS 9500 (Ludlow, 2011; Pauwels, 2012; Rottke, 2013)

Carestream 18 ・ 20 90 108 150c

DCT PRO (Qu, 2012a)

VATECH 19 ・ 20 90 105 254

i-CAT FLX (Ludlow, 2013)


i-CAT NG (Davies, 2012. Grunheid, 2012; Ludlow, 2008; Morant, 2013; Roberts, 2009)

Imaging Sciences 17 ・ 23 120 18.5 71c

Iluma Elite (Ludlow, 2008)

Imtec 19 ・ 19 120 152 498

NewTom 3G (Ludlow, 2008)

Cefla 19 ・ 19b 110 8.1 68

NewTom 9000 (Qu, 2012b)

Cefla 19 ・ 19b 110 automatic 95

SkyView (Pauwels, 2012)

Cefla 17 ・ 17b 90 51.5 87

ProMax Mid – stitched (Ludlow, 2015)

Planmeca 16 ・ 16 90 325 283

4707

a H ・ W = height x width. 4708

b Spherical field of view. 4709

c Extrapolated or averaged dose. 4710


206

4711

TABLE G.2— Effective doses for standard or default exposures for medium FOV CBCT 4712

units (10 to 15 cm height). 4713

Unit Name (reference)

Manufacturer

FOV Size

H ・ Wa

(cm)

kVp mAs Effective

Dose (µSv)

3D Accuitomo 170 (Theodorakou, 2012; Ludlow, 2015)

J Morita 10 ・ 14 90 87.5 229

3D Accuitomo 170 (Theodorakou, 2012; Ludlow, 2015)

J Morita 12 ・ 17 90 87.5 271

3D Accuitomo 170 (Ludlow, 2015)

J Morita 10 ・ 10 90 87.5 257

3D eXam (Schilling, 2014)


CB Mercuray (Jadu, 2010; Ludlow, 2008; Librizzi, 2011)

Hitachi 15 ・ 15b 120 150 514†

CB Mercuray (Lukat, 2013)

Hitachi 15 ・ 15 b 100 96 227

CS 9300 (Ludlow, 2015)

Carestream 13.5 ・ 17 90 45.2 184

CS 9300 (Ludlow, 2015)

Carestream 11 ・ 17 90 51.5 204

CS 9300 (Ludlow, 2015)

Carestream 10 ・ 10 90 25 76

CS 9500 (Ludlow, 2011)

Carestream 9 ・ 15 85 108 98

DCT PRO (Qu, 2012a)

VATECH 10 ・ 16 90 105 249

Galileos Comfort (Ludlow, 2008; Pauwels, 2012)

Sirona 15 ・ 15 b 85 21 67c

i-CAT Classic (Ludlow, 2008)


i-CAT FLX Imaging Sciences 11 ・ 16 120 18.5 79


207

(Ludlow, 2013)

i-CAT FLX (Ludlow, 2013)


i-CAT NG (Morant, 2013)


i-CAT NG (Morant, 2013)


i-CAT NG (Davies, 2012; Ludlow, 2008; Morant, 2013; Pauwels, 2012; Roberts, 2009; Theodorakou, 2012)


Iluma Elite (Pauwels, 2012)

Imtec 14 ・ 21 120 76 368

NewTom VG (Pauwels, 2012)

QR, Verona 10 ・ 15 110 10.4 83

NewTom VG (Theodorakou, 2012)

Cefla 11 ・ 15 110 auto 81

NewTom VGi (Pauwels, 2012; Ludlow, 2012)

QR, Verona 15 ・ 15 110 8.8 147 c

OP300 Maxio Instumentarium 13 ・ 15 90 45 102

Scanora 3D (Pauwels, 2012)

Soredex 13.5 ・ 14.5 85 48 68

4714

a H ・ W = height ・ width. 4715



4718


208

TABLE G.3— Effective doses for standard or default exposures for dento-alveolar centered small FOV CBCT units (<10 cm height). 4719

Unit Name Manufacturer

FOV Size

H ・ Wa

(cm)

kVp mAs Effective

Dose (µSv) Reference

3D eXam Kavo 8 ・ 16 120 18.5 88b Schilling (2013)

3D eXam Kavo 8 ・ 8 120 18.5 62 Schilling (2013)

i-CAT FLX Imaging Sciences 8 ・ 16 120 18.5 70 Ludlow (2013)



i-CAT NG Imaging Sciences 8 ・ 16 120 18.5 65 Grunheid (2012)

i-CAT NG Imaging Sciences 8 ・ 8 120 18.5 29 Morant (2013)

Kodak 9500 Carestream 8 ・ 15 90 108 92 Pauwels (2012)

NewTom VGi QR, Verona 8 ・ 12 110 6.14 42b Pauwels (2012)

Prexion 3D TeraRecon 8 ・ 8 90 76 189 Ludlow (2008)

ProMax 3D Planmeca 8 ・ 8 84 72 581b Suomalainen (2009); Ludlow (2008)

Promax 3D-upgraded filtration

Planmeca 8 ・ 8 84 169 138b Pauwels (2012); Theodorakou (2012)

4720


209


b Extrapolated or averaged dose. 4722

4723


210

4724

TABLE G.4— Effective doses for standard or default exposures for small FOV CBCT units (<10 cm height) maxillary views. 4725

Unit Name Mfg.

FOV Size

H ・ Wa

(cm)

Region of Interest

kVp mAs Effective


3D Accuitomo 170 J Morita 5 ・ 10 Maxilla 90 87.5 54 Pauwels (2012)

3D Accuitomo 170 J Morita 5 ・ 14 Maxilla 90 87.5 70 Theodorakou (2012)

3D eXam Kavo 4 ・ 16 Maxilla 120 18.5 33 Schilling (2013)

CB Mercuray Hitachi 10b Maxilla 120 150 125 Jadu (2010)

i-CAT FLX Imaging Sciences 6 ・ 16 Maxilla 120 18.5 32 Ludlow (2013)

i-CAT NG Imaging Sciences 6 ・ 16 Maxilla 120 18.5 36.8c Davies (2012; Morant (2013); Pauwels (2012); Roberts (2009); Theodorakou (2012)

Pan eXam Plus 3D Kavo 6 ・ 4 Maxilla 90 23 40 Schilling (2013)

Pan eXam Plus 3D Kavo 6 ・ 8 Maxilla 90 47 79 Schilling (2013)


Planmeca 5 ・ 8 Maxilla 84 192 115c Qu (2010)

Scanora 3D Soredex 7.5 ・ 10 Maxilla 85 30 46 Pauwels (2012)

3D Accuitomo 170 J Morita 4 ・ 4 Maxillary anterior

90 87.5 32 Theodorakou (2012)


211

CS 9000 Carestream 4 ・ 5 Maxillary anterior

70 107 19 Pauwels (2012)

PaX-Uni3D VATECH 5 ・ 5 Maxillary anterior

85 120 44 Pauwels (2012)


Planmeca 4 ・ 5 Maxillary anterior

84 120 10 Al-Okshi (2013)

Veravieweposcs 3D J Morita 4 ・ 4 Maxillary anterior

80 47.5 21 Al-Okshi (2013)

4726




4730


212

TABLE G.5— Effective doses for standard or default exposures for small FOV CBCT units (<10 cm height) mandibular views. 4731

Unit Name Manufacturer

FOV Size

H ・ Wa

(cm)

Region of Interest

kVp mAs Effective


3D eXam Kavo 4 ・ 16 Mandible 120 18.5 38 Schilling (2013)

3D eXam Kavo 5 ・ 10 Mandible 120 18.5 56b Jeong (2012)

AZ3000CT Asahi 7 ・ 7 Mandible 85 102 332 Jeong (2012)

CB Mercuray Hitachi 10 Mandible 120 150 414b Jadu (2010); Ludlow (2008)

DCT PRO VATECH 7 ・ 16 Mandible 90 105 180 Qu (2012a)

i-CAT FLX Imaging Sciences 6 ・ 16 Mandible 120 18.5 61 Ludlow (2013)

i-CAT NG Imaging Sciences 6 ・ 16 Mandible 120 18.5 53b Davies (2012); Morant (2013); Pauwels (2012); Roberts (2009); Theodorakou (2012)

Implagrapy VATECH 5 ・ 8 Mandible 80 66.5 83 Jeong (2012)

Pan exam Plus 3D Kavo 6 ・ 4 Mandible 90 23 49 Schilling (2013)

Pan exam Plus 3D Kavo 6 ・ 8 Mandible 90 47 110 Schilling (2013)

Picasso Trio VATECH 7 ・ 12 Mandible 85 91 81 Pauwels (2012)


Planmeca 5 ・ 8 Mandible 84 192 150b Qu (2010)


213

Scanora 3D Soredex 7.5 ・ 10 Mandible 85 30 47 Pauwels (2012)

3D Accuitomo 170 J Morita 4 ・ 4 Mandibular posterior

90 87.5 43 Pauwels (2012)

CS 9000 Carestream 4 ・ 5 Mandibular posterior

70 107 40 Pauwels (2012)

Veravieweposcs 3D J Morita 4 ・ 4 Mandibular posterior

80 47 22 Al-Okshi (2013)

4732


bExtrapolated or averaged dose. 4734


214

TABLE G.6— Effective doses for standard or default exposures for small FOV CBCT Units (<10 cm height) mandibular views. 4735

Unit Name Manufacturer FOV Size

H ・ Wa (cm) Region of Interest

kVp mAs Effective


3D eXam Kavo 4 ・ 16 Mandible 120 18.5 38 Schilling (2013)

3D eXam Kavo 5 ・ 10 Mandible 120 18.5 56 b Jeong (2012)

AZ3000CT Asahi 7 ・ 7 Mandible 85 102 332 Jeong (2012)

CB Mercuray Hitachi 10 Mandible 120 150 414 b Jadu (2010); Ludlow, 2008)

DCT PRO VATECH 7 ・ 16 Mandible 90 105 180 Qu (2012a)

i-CAT FLX Imaging Sciences 6 ・ 16 Mandible 120 18.5 61 Ludlow (2013)

i-CAT NG Imaging Sciences 6 ・ 16 Mandible 120 18.5 53 b Davies (2012); Morant (2013); Pauwels (2012); Roberts (2009); Theodorakou (2012)

Implagrapy VATECH 5 ・ 8 Mandible 80 66.5 83 Jeong (2012)

Pan eXam Plus 3D Kavo 6 ・ 4 Mandible 90 23 49 Schilling (2013)

Pan eXam Plus 3D Kavo 6 ・ 8 Mandible 90 47 110 Schilling (2013)

Picasso Trio VATECH 7 ・ 12 Mandible 85 91 81 Pauwels (2012)


Planmeca 5 ・ 8

Mandible 84 192 150 b Qu (2010)


215

Scanora 3D Soredex 7.5 ・ 10 Mandible 85 30 47 Pauwels (2012)

3D Accuitomo 170 J Morita 4 ・ 4

Mandibular posterior

90 87.5 43 Pauwels (2012)

CS 9000 Carestream 4 ・ 5

Mandibular posterior

70 107 40 Pauwels (2012)

Veravieweposcs 3D J Morita 4 ・ 4 Mandibular posterior

80 47 22 Al-Okshi (2013)

4736


b Extrapolated or averaged dose. 4738


216

TABLE G.7— Effective dose was statistically associated with FOV size (p = 0.0109) Tukey HSD 4739

demonstrated substantial differences between large and small FOVs. 4740

Level Least Sq Mean (µSv)

Large A 240

Medium A B 149

Small B 92

4741


217

TABLE G.8— Salivary gland dose was not associated with FOV size (p = 0.8701). 4742

Level Least Sq Mean (µGy)

Large A 3,336

Medium A 2,779

Small A 2,754

4743


218

TABLE G.9—Thyroid dose (µGy) was statistically associated with FOV size (p = 0.0299). 4744

Tukey HSD demonstrated substantial differences between large and small FOVs. 4745


Large A 1,450

Medium A B 645

Small B 475

4746


219

TABLE G.10—Brain dose (µGy) was statistically associated with FOV size (p = 0.0047). Tukey 4747

HSD demonstrated substantial differences between large and small FOVs. 4748


Large A 2,159

Medium A B 1,101

Small B 211

4749


220

TABLE G.11—Small FOV maxillary versus mandibular doses were not statistically different by 4750

effective dose (p = 0.0566), brain (p = 0.3696), or salivary glands (p = 0.1987). Substantial 4751

differences in thyroid dose are present (p = 0.0407). 4752


Mandible 616

Maxilla 121

4753


221

Appendix H 4754

4755

Dental X-Ray Evaluation by Qualified Expert 4756

4757

H.1 Radiation Safety 4758

4759

Radiation Safety should be evaluated based on integrated exposure measurements using a 4760

dosimeter, taken at various locations within and near the x-ray source. It may be necessary to 4761

increase the milliamperage-seconds to obtain a reading on your survey instrument. Inquire about 4762

workload with the staff, controlled or noncontrolled occupancy of areas near x-ray sources, and 4763

verify by reviewing representative patient logs. These should be readily available on digital 4764

systems. The qualified expert should document that radiation exposures to occupationally 4765

exposed persons and the general public are in compliance with the applicable regulations. 4766

4767

CBCT systems are often located where panoramic units were previously installed. However, 4768

the scattered radiation dose from CBCT is substantially higher than for panoramic units (about 4769

an order of magnitude), due to the significantly larger field of view exposed in CBCT systems. 4770

Calculate the exposure to persons in the vicinity of the x-ray source following the principles of 4771

NCRP Report No. 147 and information provided in this report. While exposures and workloads 4772

may remain consistent from year-to-year for intraoral x-ray units, increased utilization of CBCT 4773

systems in recent years make it essential for the qualified expert to evaluate personnel exposure 4774

during each annual survey. At the very least, the qualified expert should recalculate estimated 4775

weekly exposures using initial area survey measurements and recent workload data. Results 4776

should be compared with requirements from the local jurisdiction. Pay particular attention to 4777

personnel who may be working within line of sight of a CBCT unit or in an adjacent room, and 4778

make appropriate recommendations to assure ALARA. 4779


222

4780

H.2 Evaluation of the Image Receptor and Dose 4781

4782

If the facility is using dental film, determine whether they are using D-speed film, E-speed 4783

film, F-speed film , or what is referred to as “E-F-speed” film. This may require some detective 4784

work, if the film is purchased by mail in bulk. While many facilities have converted to digital 4785

image receptors, recent data shows that among those still using film 78 % continue to use D 4786

speed film (Farris and Spelic, 2015). The image quality for E-, F-, and E-F-speed films is similar 4787

to that obtained with D-speed film (Bernstein, 2003; FDA, 2014; Ludlow, 2001; Syriopoulos, 4788

2001) at approximately one-half of the radiation dose (Table H.1). More information on the 4789

different speed films and image quality can be found at http://diquad.com/Tips.html. 4790

4791

Table H.1 provides other helpful information.. The average exposure for D-speed film is 4792

~2.3 mGy. This is much higher than necessary. D-speed film should be on the order of 1.50 to 4793

1.95 mGy (Table 6.1). In other words, there is no justifiable reason for dental doses to routinely 4794

exceed 1.95 mGy for D-speed film. Facilities that are using ‘D’ speed film should be advised of 4795

the lower doses possible with the use of ‘E’ or ‘F’ speed films. They should also be advised of 4796

the potential for low doses with digital-based equipment as shown in the table. 4797

4798

H.3 Film Processing Conditions and Quality 4799

4800

Processing conditions and quality have been found to vary considerably in the dental imaging 4801

community. Verify that proper time-temperature developing is being used. Film processing tips 4802

are included in http://diquad.com/Tips.html. Film processing is usually the weakest link in the 4803

imaging chain, with under-processing resulting in low contrast radiographs and increased 4804

patient doses. The histograms from the recent NEXT survey (Farris and Spelic, 2015) clearly 4805

demonstrate the broad range of patient doses and suboptimal film processing (approximately 4806

one-third of the facilities produce films with inferior contrast). To assist with testing processing 4807

conditions, consider an inexpensive step wedge or dental radiographic quality control device for 4808

4809

4810


223

TABLE H.1— Dental bitewing x-ray exposures (mR) for 2001, 2005, 2009.a 4811

Dental Bitewing for 2009 (n = 7,205)

Speed Total % of Total Average SD Highest

D 3,483 55 % 256 99 2,150

E 1,001 16 % 162 72 1,320

F 774 12 % 148 63 520

Digital 1,947 31 % 105 59 693

4812


Type Total % of Total Average SD Highest

D 3,084 49 % 258 93 860

E 1,118 18 % 162 70 786

F 500 8 % 140 67 952

Digital 1,623 26 % 106 58 712


Type Total % of Total Average SD Highest

D 5,127 81 % 262 106 3,308

E 1,674 26 % 161 68 675

F 510 8 % 148 58 650

Digital 1,289 20 % 110 64 560

4813

aCourtesy New York State Department of Health. 4814

4815


224

dental film processing quality. The dental radiographic quality control device is also helpful in 4816

assuring appropriate initial film exposure technique selection and processing conditions 4817

(Valachovic, 1981). 4818

4819

H.4. Evaluation of the X-Ray Generator and Output 4820

4821

The x-ray generator can be evaluation using standard techniques. Be sure that the radiation 4822

detector is properly positioned, and sized appropriately to include the complete x-ray beam. 4823

Modern units typically operate at only a single kilovoltage, 60 to 70 kVp, and a single 4824

milliamperage, 6 to 10 mA. Be sure to account for any effect of very short radiographic 4825

exposure times, i.e., overshoot of output for the first few milliseconds.. 4826

4827

H.5 Evaluation of the Beam Collimation 4828

4829

For intraoral radiographic units, consider recommending rectangular collimation, which has 4830

been shown to reduce effective dose four to five times by providing an x-ray beam that more 4831

closely approximates the rectangular image receptor (White and Pharoah, 2014). The qualified 4832

expert’s experience with the benefits (image quality and radiation safety) derived from 4833

collimating the x-ray beam to the image receptor in body radiography and fluoroscopy (for 4834

example), will be directly applicable here. 4835

4836

Evaluating collimation for panoramic or CBCT systems requires some pre-planning, and 4837

may be accomplished using GAF Chromic Film and the equipment manufacturer’s 4838

specifications for geometry. Figure H.1 shows how this may be accomplished. 4839

4840

H.6 Occupational Radiation Exposure Assessment 4841

4842

While many dental offices are not required to use personal dosimetry, increased utilization 4843

of digital and CBCT imaging may warrant a renewed assessment of occupational exposure with 4844

personnel dosimetry. The qualified expert should advise the facility management whether 4845

occupational dosimetry is appropriate or is required by state or local regulations. 4846

4847


225

4848

4849

4850

4851

4852

4853

4854

4855

4856

Fig. H.1. The photo on the left shows the self-developing x-ray film taped to the surface of 4857

the x-ray tube cover. The images at the right show two strips, following exposure (photos 4858

courtesy R. Pizzutiello). 4859

4860


226

Appendix I 4861

4862

Radiation Risk Assessment 4863

4864

I.1 Introduction 4865

4866

The assignment of risk of biological damage from radiation has long been an arena of 4867

considerable controversy. Damage from moderate to high doses are well documented and the 4868

risk well quantified. However, risks from small and very small doses are inferred from data for 4869

moderate to high doses based on one of several risk models. While there is growing new 4870

evidence, and strengthening of existing evidence, for damage from very low doses of radiation, 4871

there is considerable controversy over the methodology and conclusions in many of these 4872

studies, and the application of these population risks to individuals HPS, 2016; NCRP, 2010b; 4873

UNSCEAR, 2012). This is especially true in oral and maxillofacial imaging, where radiation 4874

doses (except for high resolution moderate-to-large field-of-view cone-beam CT imaging) are 4875

considerably smaller than in other fields of medical imaging. Nonetheless, dentistry as a 4876

profession has a responsibility for the radiation safety of the population-at-large as well as for 4877

the individual seeking care. 4878

4879

In the time since NCRP-145, Radiation Safety in Dentistry, there have been significant 4880

advances in the understanding of radiogenic DNA damage and repair, based on considerable 4881

laboratory research in genetics and molecular biology. Solidification of long-term studies of 4882

Japanese atomic bomb survivors, have increased confidence in risk estimates at low radiation 4883

doses. The understanding of genetic instability has given us a better understanding of the long 4884

latent periods associated with radiation carcinogenesis and heritable defects. Substantial 4885

publications elucidating the uncertainties in risk estimation have recently been published 4886

(NA/NRC, 2006; UNSCEAR, 2015b). Recent retrospective studies on large populations of 4887

head-irradiated children in the UNITED KINGDOM and in Australia, while eliciting some 4888

controversy over their epidemiologic methodology, have supported the existing risk modeling 4889

for radiogenic brain, thyroid, salivary gland and leukemia neoplasms (Brenner and Hall, 2007; 4890


227

Mathews et al., 2013). A recent publication provides a clear and comprehensive review of 4891

cancer risks from diagnostic imaging (Linet et al., 2012). 4892

4893

There must always be a balance between the benefit to the patient and the risk of damage to 4894

the patient when diagnostic x-radiation is used for imaging. There are many steps, 4895

recommended in this report, to maintain, or improve, the diagnostic quality of the images while 4896

minimizing the radiation dose to the patient – a patient care application of the ALARA 4897

principle. The goal is always to maximize diagnostic efficacy while minimizing radiation dose. 4898

4899

I.2 Definitions 4900

4901

I.2.1 Stochastic Effects 4902

4903

These low-dose effects consist almost entirely of cancer and mutation. They are generally 4904

rare events, occurring only after a latent period of years to decades for cancer and generations 4905

for genetic effects. Thus, they present practical problems in the design of studies for their 4906

investigation. In the cohort of 87,000 Japanese atomic-bomb survivors, there were 9335 deaths 4907

from solid cancers between 1950 and 1997 attributable to radiation exposure (Preston et al., 4908

2003). Recent analyses have confirmed and reinforced the risk estimates from the atomic-bomb 4909

survivor studies (Douple et al., 2011; Preston et al., 2007). 4910

4911

Risks from low doses have been estimated by extrapolation from high dose data (ICRP, 4912

1991; NA/NRC, 1990; 2006; NCRP, 1993b; UNSCEAR, 2000; 2015a). There has been 4913

considerable disagreement in the literature concerning the model used for such extrapolation to 4914

dose levels used in diagnostic imaging (AAPM, 2012). For radiation protection purposes, 4915

NCRP and most regulatory agencies worldwide use the most conservative, patient- and 4916

population-oriented modeling, and recommend use of the linear nonthreshold dose-response 4917

model for estimating the nominal risk of low doses (Douple et al., 2011; NA/NRC, 2006; 4918

NCRP, 1993b, 2009; Puskin, 2009; UNSCEAR, 2015a). 4919

4920


228

I.2.2 Deterministic Effects (Tissue Reactions) 4921

4922

Deterministic effects (also referred to as tissue reactions) result from structural or functional 4923

damage to tissue caused by irradiation. The type and amount of tissue damage increases with 4924

dose once a threshold is passed. When sufficient numbers of functional parenchymal cells in a 4925

given organ or tissue are killed, then the function of that organ or tissue may be impaired or 4926

destroyed. If that function is vital, then the injury may be life threatening to the organism. 4927

Classic examples of tissue reactions are the acute radiation syndromes (Rubin and Casarett, 4928

1968), non-melanotic skin carcinogenesis and cataractogenesis. The dose thresholds for tissue 4929

reactions are sufficiently large that it is highly unlikely that a dental worker or a patient would 4930

suffer a tissue reaction, provided that common radiation safety precautions are followed. 4931

4932

I.2.3 Dose Language 4933

4934

In this document, and throughout radiation biology and radiation health physics literature, 4935

the terms high, moderate, low and very low radiation doses or exposures are used. In this 4936

document, the terms are defined in effective dose units as follows (UNSCEAR, 2015a): 4937

4938

average annual background radiation dose in the United States = 6.2 mSv; 4939

high = greater than ~1 Sv; 4940

moderate = ~100 mSv to ~1 Sv; 4941

low = ~10 to ~100 mSv (dose to an individual from multiple whole-body CT scans 4942

and from multiple large field-of-view, high resolution CBCT scans); and 4943

very low = less than ~10 mSv [dose to an individual from conventional radiology (i.e., 4944

without CT or fluoroscopy)]. 4945

4946


229

I.3 Studies of Irradiated Human Populations 4947

4948

I.3.1 Introduction 4949

4950

The nature of the risk of carcinogenesis at low radiation doses has long been the subject of 4951

controversy. Major publications during recent years have focused on uncertainties in risk 4952

estimation at low doses (NCRP, 2012; UNSCEAR, 2015b). Several models have been 4953

developed to explain low dose risk, and these are shown in the graph below. 4954

4955

The committee finds the linear nonthreshold (LNT) model to be a computationally 4956

convenient starting point. Actual risk estimates improve upon this simplified model by using a 4957

dose and dose-rate effectiveness factor (DDREF), which is a multiplicative adjustment that 4958

results in downward estimation of risk and is roughly equivalent to using the line labeled 4959

“Linear Nonthreshold” (low dose rate). The latter is the zero-dose tangent of the linear-4960

quadratic model. While it would be possible to use the linear-quadratic model directly, the 4961

DDREF adjustment to the linear model is used to conform with historical precedent dictated in 4962

part by simplicity of calculations. In the low-dose range of interest, there is essentially no 4963

difference between the two (adapted from Brenner and Elliston, 2004). 4964

4965

A meta-analysis of data from cohorts with prolonged occupational exposure has indicated 4966

that risks per unit dose are consistent with those derived from the Life Span Study (LSS) cohort 4967

of the atomic bombing survivors (Jacob et al., 2009; UNSCEAR, 2015b). Recent evidence from 4968

continued analysis of cancer in Japanese survivors of the atomic bombings, radiation workers in 4969

the UNITED KINGDOM, Canada and the United States, and children exposed to diagnostic 4970

head CT exposures in Australia have provided substantial direct evidence that solid 4971

tumorigenesis follows the linear model and that leukemogenesis follows the linear-quadratic 4972

model. 4973

4974

Most of the information on radiation risks therefore still comes from studies of populations 4975

with medium to high doses, with the notable exceptions of childhood cancer risk following in 4976

utero exposures and thyroid cancer risk following childhood exposures, for which significant 4977

increases have been shown consistently in the low- to medium-dose range (NA/NRC, 2006). 4978

4979

4980


230

4981 Fig. I.1. Models of low dose radiogenic cancer risk (NA/NRC, 2006). 4982

4983

4984


231

Brenner et al. (2007), estimate that from 1.5 to 2 % of all cancers in the United States may 4985

be attributable to the radiation from CT studies. An annual growth rate of >10 % y–1 for CT 4986

procedures in the United States (NCRP, 2009) appears to be mirrored in the growth rate of 4987

CBCT since its introduction (Farris and Spelic, 2015). 4988

4989

I.3.2 Atomic Bomb Survivor Lifetime Studies 4990

4991

Survivors of the atomic bombings of Hiroshima and Nagasaki and their offspring comprise 4992

the single largest cohort exposed to ionizing radiation that is currently being followed, and are 4993

the major source of lifetime studies of radiation-induced cancers, other diseases, and life 4994

shortening. A major reevaluation of the dosimetry at Hiroshima and Nagasaki has recently been 4995

completed that lends more certainty to dose estimates and provides increased confidence in the 4996

relationship between radiation exposure and the health effects observed in this population. 4997

4998

Solid tumors that are well described by the linear model include female breast and thyroid, 4999

while leukemias appear to fit the linear-quadratic model best. This is shown in the graph below. 5000

5001

Additional new information is also available from radiation worker studies, medical 5002

radiation exposures, and populations with environmental exposures. Although the cancer risk 5003

estimates have not changed greatly since the 1990 BEIR V report (NA/NRC, 1990), confidence 5004

in the estimates has risen because of the increase in epidemiologic and biological data available 5005

to the committee (Douple et al., 2011; NA/NRC, 2006). 5006

5007

I.3.3 Children Irradiated for Tinea Capitis and Enlarged Thymus 5008

5009

Studies on the risk of thyroid cancer following irradiation of the head for tinea capitis has 5010

been extensively followed, from post-WW2 through 1986. These studies have shown a clear 5011

risk when radiation occurred in childhood – especially before 10 y of age. There was a fourfold 5012

increase in the incidence of thyroid cancer and a twofold increased incidence in benign thyroid 5013

tumors (Ron et al., 1989). Additionally, there was a 4.5-fold increase in the incidence of 5014

5015


232

5016

5017

5018

5019

5020

5021

5022

5023

5024

5025

5026

5027

5028

5029

Fig. I.2. Excess relative risks of solid cancer for Japanese atomic bomb survivors. Plotted 5030

points are estimated excess relative risks of solid cancer incidence (averaged over sex and 5031

standardized to represent individuals exposed at age 30 y who have attained age 60 y) for 5032

atomic bomb survivors, with doses in each of 10 dose intervals, plotted above the midpoints of 5033

the dose intervals. Vertical lines represent approximate 95 % confidence intervals. Solid and 5034

dotted lines are estimated linear and linear-quadratic models for excess relative risk, estimated 5035

from all subjects with doses in the range 0 to 1.5 Sv. A linear-quadratic model will always fit 5036

the data better than a linear model, since the linear model is a restricted special case with the 5037

quadratic coefficient equal to zero. For solid cancer incidence however, there is no statistically 5038

significant improvement in fit due to the quadratic term. It should also be noted that in the low-5039

dose range of interest, the difference between the estimated linear and linear-quadratic models 5040

is small relative to the 95 % confidence intervals. The insert shows the fit of a linear-quadratic 5041

model for leukemia to illustrate the greater degree of curvature observed for that cancer 5042

(NA/NRC, 2006) (adopted from NA/NRC, 2006, Figure ES-1). 5043

5044


233

malignant salivary gland tumors and a 2.6-fold increase in benign salivary gland tumors in the 5045

same population (Modan et al., 1998). 5046

5047

Children in Rochester, NY who received X-ray treatment for enlarged thymus glands 5048

between 1926 and 1957 prior to six months of age showed statistically significant increases of 5049

both benign and malignant thyroid tumors (Shore et al., 1985), as well as tumors of bone, 5050

nervous system, salivary glands, skin and female breast (Hildreth et al., 1985). The most recent 5051

study (Shore et al., 1993) again showed increased risk of thyroid cancer, even at low doses. 5052

5053

These data all fit well with a LNT model for thyroid carcinogenesis in children. 5054

5055

I.3.4 Females Receiving Fluoroscopy for Tuberculosis Treatment Follow-up 5056

5057

Significant increases in breast cancer was found in a cohort study of 64,172 tuberculosis 5058

patients of whom 25,007 received highly fractionated radiation from repeated fluoroscopy for 5059

lung collapse treatment of tuberculosis. There was a significant increase in risk of breast cancer 5060

in a dose dependent manner, commensurate with the LNT model (Boice et al., 1991). The 5061

excess cancer risk did not occur until 15 y after exposure, and held for over 50 y (Boice et al., 5062

1991a; Davis et al., 1989; Howe and McLaughlin, 1996; Miller et al., 1989; NA/NRC, 2006) 5063

5064

I.3.5 United Kingdom National Registry of Radiation Workers 5065

5066

This study has provided the most recent, direct estimates of long-term, low-dose, low-LET 5067

radiation effects on occupationally exposed populations, and has provided estimates of 5068

leukemia and all solid cancer risks. Risks, comparable to those in the atomic bomb survivors, 5069

range from slightly below to twice above those estimated using the current linear, nonthreshold 5070

model. The ERR/Gy calculated from the Nuclear Industry Workers study was comparable with 5071

risk estimates for atomic bomb survivors for both solid tumors and leukemias (Muirhead et al., 5072

2009). 5073

5074

5075


234

5076

5077

Fig. I.3. Incidence rate ratio (IRR) for all types of cancer in exposed versus unexposed 5078

individuals, by number of CT scans (Matthews et al., 2013). 5079

5080


235

I.3.6 2013 Australian CT Study of Electronic Medicare Data 5081

5082

This study examined 680,000 children receiving CT scans from 1985 to 2005 versus 5083

10.9 million controls. Overall cancer incidence was 24 % higher in those receiving CT scans, 5084

and the incidence increased with increasing numbers of scans, and was greater for children 5085

<5 y. These results confirmed U.K. Radiation Workers study of increased incidence of 5086

leukemia and brain cancer, and added other solid tumors (Mathews et al., 2013). 5087

5088

I.4 Effects of In Utero Exposure 5089

5090

In the case of in utero exposure (exposure of the fetus during pregnancy) during diagnostic 5091

radiography, it was reported that excess cancers could be detected at doses as low as 10 mSv 5092

(Doll and Wakeford, 1997). 5093

5094

In the domain of conventional diagnostic dental radiology, the in utero radiation dose is so 5095

small as to be essentially negligible. The measured dose in utero from a full-mouth series of 5096

intraoral images is 0.25mSv (White and Pharoah, 2014). Thus, we project that the risk to a 5097

developing embryo/fetus from conventional dental imaging is negligible. Risk from CBCT 5098

examinations can range from very small when small FOV and low dose parameters are used, to 5099

comparable to MDCT when large FOV and high dose parameters are used. 5100

5101

Recent reports based on atomic bomb survivors compared the risk estimates for those 5102

exposed in utero to those exposed during childhood as to the incidence of solid cancer at ages 5103

12. These studies suggest that in utero exposure does not confer greater adult cancer risk than 5104

childhood exposure. However, better understanding of cancer risks from in utero exposures and 5105

further follow-up of those exposed in utero and as children to older ages is needed” (Douple 5106

et al., 2011; Linet, 2012). 5107

5108

I.5 Effects on Children 5109

5110

Children have sensitivity anywhere from 2x to 10x greater than adults, depending on the 5111

cancer being considered. This is largely a function of their tissues, composed of cells with 5112


236

higher proliferative rates, less differentiation and longer mitotic future. The risk is greater the 5113

younger the child, and diminishes rapidly after 10 to 15 y of age. 5114

5115

Figure I.4 shows the risk differences due to age (Brenner and Hall, 2007). 5116

5117

I.5.1 Joint Commission Report (2011) 5118

5119

In August, 2011, The Joint Commission published a Sentinel Event Alert (TJC, 2011). They 5120

cited the near doubling of the U.S. population’s total exposure to ionizing radiation, specifying 5121

the significant increases in CT imaging, and used dose and risk estimates to emphasize the 5122

importance of ALARA and Image Gently guidelines when imaging adult and pediatric patients. 5123

This report estimated that 72 million CT scans in United States in 2007 could lead to 29,000 5124

future cancers – this would be 2 % higher than the normal frequency in the general population. 5125

This calculation assumed 2007 ICRP tissue weighting factors and LNT model for low dose 5126

carcinogenesis (UNSCEAR, 2015a). Cone-beam CT scans of children and adolescents were not 5127

specifically considered in this report, but the doses delivered in high-resolution, large field-of-5128

view CBCT examinations are of the same order of magnitude as the CT scans evaluated in this 5129

report. 5130

5131

I.5.2 2012 U.K. Study of Head CT Scans in Children 5132

5133

A recent study published Pearce et al. (2012) retrospectively examined a large cohort of 5134

patients receiving CT examinations during childhood for subsequent development of brain 5135

cancer and leukemia. This study showed that “use of CT scans in children [which] deliver 5136

cumulative doses of ~50 mGy might almost triple the risk of leukemia and doses of ~60 mGy 5137

might triple the risk of brain cancer” 5138

5139

These estimates agree reasonably with the 2001 estimates based on the atomic bomb 5140

survivor data (Preston et al., 1994; Ron et al.,1988). 5141

5142


237

5143

5144

Fig. I.4. Lifetime risks of radiogenic cancer versus age at time of a single head CT study. 5145

The risk of brain cancer and other solid cancers is considerably greater in children under the 5146

age of 15 y. A similar trend, but with substantially lower risk, applies to leukemia. 5147

5148


238

5149

TABLE I.1—U.K. CT study: Absolute risks versus atomic-bomb based estimates for a pediatric 5150

head CT scan, circa 1995.a 5151

U.K. CT study

(10 y follow-up)

U.K. CT study

(corrected to lifetime

follow-up)

Atomic-Bomb Estimates

(corrected to lifetime

follow-up)

Leukemia 1 in 10,000 1 in 7,500 1 in 10,000

Brain tumor 1 in 10,000 12 in 10,000 5 in 10,000

Pearce et al. (2012) Brenner and Hall (2007)

5152

aHall, E. (2012). Presentation at the American Academy of Oral and Maxillofacial Radiology 5153

Annual Session (Columbia University, New York). 5154

5155


239

I. Heritable Genetic Effects 5156

5157

Genetic instability is a molecular hallmark of radiogenic DNA damage. The transmission of 5158

such genetic instability across human generations is unknown at the present time. There is 5159

evidence for heritable genetic effects of radiation from animal experiments; however, these 5160

results to not apply directly to human beings. The risk estimates in animals are very small 5161

relative to the baseline rate of genetic diseases in the population, and are ~0.4 to 0.6 % of 5162

baseline risk per gray (NA/NRC, 2006). 5163

5164

In the atomic bomb survivor LSS, children from exposed parents (8,322) and unexposed 5165

parents (7,976) have been followed extensively in a long-term study initiated by Neel and 5166

Schull in the 1950s (Neel and Schull, 1956). Thus far, the level of mutagenesis, if present, is not 5167

detectable with the sensitivity of current methods. Additionally, there is no evidence of an 5168

increase of multifactorial diseases (e.g. hypertension, type-2 diabetes mellitus, 5169

hypercholesterolemia, ischemic heart disease, stroke) in this cohort. 5170

5171

The radiation doses for dentomaxillofacial imaging are in the microgray to milligray range 5172

Tissues not included in maxillofacial imaging effective dose calculations account for <2 % of 5173

the effective dose, and <0.1 % with use of a lap apron. Thus, heritable genetic effects from 5174

conventional dental imaging are essentially negligible. 5175

5176

5177

I.7 Risk from Traditional Oral and Maxillofacial Imaging: Intraoral, 5178

Panoramic, and Cephalometric 5179

5180

Doses from traditional dentomaxillofacial imaging are given in Appendix E and in Sections 5181

7.1.6, 8.1.1.1, and 8.2.1.1 of this report. These doses are in the microgray and milligray ranges. 5182

While the contribution of tissues in the maxillofacial area to the effective dose have been 5183

significantly increased by the revised ICRP (2007) tissue weighting factors, the doses from 5184

properly acquired intraoral, panoramic and cephalometric images are extremely small. 5185

Nevertheless, prudent practice and ALARA principles demand that the dentist use the dose 5186


240

reduction techniques, stated in this report, to minimize the dose to the patient, staff and public. 5187

These techniques also result in high quality diagnostic images. 5188

5189

I.8 Risk from CBCT Imaging 5190

5191

In children, the principle carcinogenesis risks from dentomaxillofacial imaging involve 5192

brain, thyroid and salivary glands. In adults, the risk primarily involves salivary glands as the 5193

risk of thyroid and brain tumors is very small. A comprehensive and detailed demonstration of 5194

the variety of doses that can result from CBCT examinations are shown in Appendix G and 5195

Section 9.1.1 of this report. 5196

5197

The revision of the tissue weighting factors by ICRP in 2007 have resulted in a 10 % 5198

increase in the weight of tissues located in the maxillofacial area, and a 28 % increase in the 5199

weight adjusted for distribution of these tissues. 5200

5201

Comparison of doses with MDCT show that CBCT doses can equal or exceed MDCT 5202

doses, especially when large FOV and/or high resolution presets are used. Using high resolution 5203

presets on small, medium and large field-of-view CBCT acquisitions can result in radiation 5204

doses that are greater than multi-detector CT scans of the head and neck. 5205

5206

Thus, risks for dental CBCT imaging are greater than previously thought and the risks for 5207

head CT exams as promulgated in the above studies can apply to dental CBCT imaging. 5208

5209

I.9 Other Risks in Daily Living for Comparison 5210

5211

There are many tables showing various risks from activities of daily living, ranging from 5212

where you live, what type of building you live in, your work, travel, and other habits. These can 5213

be effectively related to risks from diagnostic dental imaging. Background equivalents in one 5214

case and one-in-a-million risks in the other are shown in Tables I.3 and I.4. Most conventional 5215

dentomaxillofacial imaging, excluding CBCT, is considered to be approximately a one-in-a-5216

million risk of death during one’s lifetime from cancer. 5217

5218


241

TABLE I.2—Summary of published data for CT and CBCT effective doses (2007 ICRP tissue 5219

weighting factors) adult phantoms – all protocols. 5220

5221

5222

5223

5224

5225

5226

5227

5228

5229

Scan Type Effective Dose Range (µSv)

Large FOV CBCT 46 – 1,073

Medium FOV CBCT 9 – 560

Small FOV CBCT 5 – 652

Medium FOV MDCT 534 – 860


242

TABLE I.3—Effective dose from radiographic examinations and equivalent background 5230

exposure (White and Pharoah, 2014). 5231

Examination Effective Dose (µSv) Equivalent Background

Exposure (d)

INTRAORAL a

RECTANGULAR COLLIMATION

Posterior bitewings: PSP or F-speed film 5 0.6

Full-mouth: PSP or F-speed film 35 4

Full-mouth: CCD sensor (estimated) 17 2

ROUND COLLIMATION

Full-mouth: D-speed film 388 46

Full-mouth: PSP or F-speed film 171 20

Full-mouth: CCD sensor (estimated) 85 10

EXTRAORAL

Panoramic a,b,c 9 – 24 1 – 3

Cephalometric a,b,d 2 – 6 0.3 – 0.7

CONE BEAM CT e,f

Large field of view 68 – 1,073 8 – 126

Medium field of view 45 – 860 5 – 101

Small field of view 19 – 652 2 – 77

MULTISLICE CT

Head: Conventional protocol f,g,h,i 860 – 1,500 101 – 177

Head: Low-dose protocol f,h 180 – 534 21 – 63

Abdomen g 5,300 624

Chest g 5,800 682


243

Plain films j

Skull 70 8

Chest 20 2

Barium enema 7,200 847

5232

CCD = charge-coupled device 5233

PSP = photostimulable phosphor 5234

5235

aData from Ludlow JB, Davies-Ludlow LE, White SC: Patient risk related to common dental radiographic examinations: 5236

The impact of 2007 International Commission on Radiological Protection Recommendation Regarding dose calculation, J 5237

Am Dent Assoc 139:1237·1243, 2008. 5238

bData from Lecomber AR, Yoneyama Y, Lovelock DJ et al: Comparison of patient dose from imaging protocols for dental 5239

implant planning using conventional radiography and computed tomography, Dentomaxillofac Radio 30:255·259, 2001. 5240

cData from Ludlow JB, Davies-Ludlow LE, Brooks SL: Dosimetry of two extraoral direct digital imaging devices: 5241

NewTom cone beam CT and Orthophos Plus OS panoramic unit, Dentomaxillofac Radio 32:229–234, 2003. 5242

dData from Gijbels F, Sanderink G, Wyatt J et al: Radiation doses of indirect and direct digital cephalometric radiography, 5243

Br Dent1 197:149·152, 2004. 5244

eData from Pauwels R, Beinsberger J, Callaert B et al: Effective dose range for dental cone beam computed tomography 5245

scanners, EurJ Radio 81 :267·271, 2012. 5246

fData from Ludlow JB, lvanovic M: Comparative dosimetry of dental CBCT devices and 64-slice CT for oral and 5247

maxillofacial radiology, Oral Surg Oral Med Oral Pathol Oral Radio Endod 106:1 06·114, 2008. 5248

gData from Shrimpton PC, Hillier MC, Lewis MA et al: National survey of doses from CT in the UK: 2003, Br J Radio 5249

79:968·980, 2006. 5250

hData from Loubele M, Jacobs R, Maes F et al: Radiation dose vs. image qualily for low-dose CT protocols of the head for 5251

maxillofacial surgery and oral implant planning, Radial Prot Dosimetry 117:211 -216, 05. 5252

iData from Loubele M, Bogaerts R, Van Dijck E et al: Comparison between effective radiation dose of CBCT and MSCT 5253

scanners for dentomaxillofacial applications, EurJ Radio 71:461·468, 2009. 5254

jData from European Commission: Referral guidelines for imaging, Radiation Protection 118, 2007. 5255

5256


244

TABLE I.4—Comparable risk table—risks that increase probability of death by one in a million 5257

(Wilson, 1979). 5258

Activity Cause of Death

Smoking 1.4 cigarettes Cancer, heart disease

Drinking 1/2 liter of wine Cirrhosis of the liver

Traveling 10 miles by bicycle Accident

Traveling 300 miles by car Accident

Flying 1,000 miles by jet Accident

Traveling 6,000 miles by jet Cancer caused by cosmic radiation

Living 2 months in average brick building Cancer caused by natural stone or radioactivity

1 chest x-ray taken in a good hospital Cancer caused by radiation

Living 2 months with a cigarette smoker Cancer, heart disease

Eating 40 tablespoons of peanut butter Liver cancer caused by aflatoxin B

Eating 100 charcoal broiled steaks Cancer from benzopyrene

Drinking 30 12 oz. cans of diet soda Cancer caused by saccharin (no longer classified as a carcinogen)

Living 5 y at site boundary of a typical nuclear power plant in the open

Cancer caused by radiation

Living 20 y near PVC plant Cancer caused by vinyl chloride (1976 standard)

Living 150 y within 20 miles of a nuclear power plant


Risk of accident by living within 5 miles of a nuclear reactor for 50 y


5259

5260


245

Appendix J 5261

5262

Radiation Quantities and Units 5263

5264

NCRP presently expresses the values of radiation quantities in the International System of 5265

Units (SI units). These units have replaced the previously used units (Table J.1) in most of the 5266

scientific literature. The quantity exposure, previously expressed in roentgens (R), has been 5267

largely replaced by the quantity air kerma (K) (an acronym for kinetic energy released per unit 5268

mass), which is expressed in the same units as absorbed dose. However, some older instruments 5269

may provide readout only in roentgens while with others either SI or the legacy units may be 5270

selected. Absorbed dose, the energy imparted by ionizing radiation to matter per unit mass, is 5271

expressed in gray (Gy) (the previous name was the rad). Equivalent dose, expressed in sievert 5272

(Sv) (the previous name was the rem), is used extensively in radiation protection. Equivalent 5273

dose is the mean absorbed dose in an organ or tissue modified by the radiation weighting factors 5274

for different types of radiation (e.g., photons, neutrons, heavy charged particles). For diagnostic 5275

x rays (including dental), the radiation weighting factor is assigned the value of one, and 5276

absorbed dose in gray is numerically equal to equivalent dose in sievert. 5277

5278

Another quantity, effective dose, is useful in comparing different dose distributions in the 5279

body. It takes into account the equivalent doses in radiosensitive organs or tissues, each 5280

modified by a tissue weighting factor that represents the relative contribution of risk of 5281

stochastic effect to that organ or tissue to total stochastic risk. The tissues receiving the higher 5282

doses in patients from dental radiography are portions of the active bone marrow, thyroid, bone 5283

surface of the skull, brain, and salivary glands. 5284

5285

Conversion factors from the previous units to SI units are given in Table J.1. Detailed 5286

discussions of these concepts are given elsewhere (Bushberg et al., 2012; Johns, 1983). 5287

5288


246

TABLE J.1—Radiation quantities and units. 5289

Quantity

SI Unitsa Previous Unitsa

Conversion

Unit Special Name Unit Special Name

Exposure C kg–1 none C kg–1 roentgen (R) 1 R = 2.58 × 10–4 C kg–1

Kerma; absorbed

dose J kg–1

gray (Gy)

1 Gy = 1 J kg–1 erg g–1

rad

1 rad = 100 erg g–1 1 Gy = 100 rad

Equivalent dose;

effective dose J kg–1

sievert (Sv)

1 Sv = 1 J kg–1 erg g–1

rem

1 rem = 100 erg g–1 1 Sv = 100 rem

5290

aC = coulomb 5291

J = joule 5292

g = gram 5293

kg = kilogram5294


247

Abbreviations, Acronyms and Symbols 5295

5296

ALARA as low as reasonably achievable 5297

ANSI American National Standards Institute College 5298

CDRH Center for Devices and Radiological Health, U.S. Food and Drug 5299

Administration 5300

CTDI computed tomography dose index used for comparing radiation outputs 5301

from CT scanners under varying conditions 5302

d distance 5303

D absorbed dose 5304

DRL diagnostic reference level 5305

ESE entrance skin exposure 5306

HERCA Heads of European Radiological Protection Competent Authorities 5307

HIPAA Health Insurance Portability and Accountability Act 5308

HT equivalent dose 5309

K kerma or air kerma 5310

kerma kinetic energy released in a mass 5311

MDCT Multi-detector computed tomography 5312

NEXT Nationwide Evaluation of X-Ray Trends 5313

NRPB National Radiological Protection Board (now known as Health 5314

Protection Agency) 5315

T occupancy factor 5316

wR radiation weighting factor 5317

wT tissue weighting factor 5318

5319


248

Glossary 5320

5321

absorbed dose (D): The energy imparted by ionizing radiation to matter per unit mass of 5322

irradiated material at the point of interest. In the System Internationale (SI), the unit is J kg–1, 5323

given the special name gray (Gy). 1 Gy = 1 J kg–1. 5324

achievable dose: A dose which serves as a goal for optimization efforts. This dose is achievable 5325

by standard techniques and technologies in widespread use, while maintaining clinical image 5326

quality adequate for the diagnostic purpose. The achievable dose is typically set at the 5327

median value of the dose distribution. 5328

air kerma (K): (see kerma). Kerma in air. In this Report, the symbol K always refers to the 5329

quantity air kerma (in place of the usual symbol Ka), followed by an appropriate subscript to 5330

further describe the quantity (e.g., KP, air kerma from primary radiation). 5331

ALARA. As low as reasonably achievable. The principle of reducing the radiation dose of 5332

exposed persons to levels as low as is reasonably achievable. 5333

alveolar bone: The bone of the maxilla (upper jaw) or mandible (lower jaw) that supports the 5334

teeth. 5335

ampere: Unit of electric current. One ampere is produced by one volt acting through a resistance 5336

of 1 ohm. 5337

anode: The positive terminal of an x-ray tube. A tungsten block embedded in a copper stem and 5338

set at an angle to the cathode (the negative terminal of an x-ray tube, from which electrons 5339

are emitted). The anode emits x rays from the point of impact of the electron stream from the 5340

cathode. 5341

area (or facility) dosimeter: A device used to estimate the absorbed dose or effective dose 5342

received by personnel, but not worn by an individual. 5343

arthrography: Radiographic evaluation of a joint after injection of radiopaque contrast material 5344

into the joint space(s). 5345

attenuation: Loss of energy from a beam of ionizing radiation by scatter and absorption. 5346

background: Ionizing radiation present in the region of interest and coming from sources other 5347

than that of primary concern (see also natural background radiation). 5348

bisecting angle technique (bisect angle geometry): A technique for the radiographic exposure 5349

of intraoral image receptors whereby the central axis of the x-ray beam is directed at right 5350

angles to a plane determined by bisecting the angle formed by (1) the long axis of the tooth 5351


249

or teeth being imaged, and (2) the plane in which the image receptor is positioned behind the 5352

teeth. 5353

bitewing radiograph: A radiographic view that shows the crown of both the upper and lower 5354

teeth in a region on the same image. This view is used to detect interproximal tooth decay or 5355

alveolar bone loss associated with periodontal disease. So named because the patient bites 5356

upon a tab or “wing” projecting from the center of the image-receptor packet. 5357

cathode: (see anode). 5358

cephalometer: A device used in obtaining cephalometric images. It consists of a source 5359

assembly, a connector arm, a head holder, and an image-receptor holder. 5360

cephalometric radiography: Images of the head, primarily the dentofacial structures, usually 5361

obtained in lateral and posteroanterior orientation. Reproducible geometry is maintained by 5362

use of a cephalometer. The images are used to measure and study maxillofacial growth and 5363

maxilla-mandible relationships. 5364

collimator (or beam-limiting device): A device that provides a means to restrict the dimensions 5365

of the useful beam. 5366

computed tomography (CT): An imaging procedure that uses multiple x-ray transmission 5367

measurements and a computer program to generate tomographic images of the patient. 5368

computed radiography (CR): A radiographic imaging technique in which an image is captured 5369

by a photostimulable phosphor and converted into a digital image. This term is generally 5370

used in medical imaging. In dental imaging, the term PSP or storage phosphor imaging is 5371

generally used (see photostimulable storage phosphor). 5372

cone: (see position indicating device). 5373

constant potential: The electrical potential formed by a constant-voltage generator 5374

contrast: 5375

subject contrast: The difference between two anatomic structures in attenuation of an x-ray 5376

beam or, where C is subject contrast, and IA and IB are beam intensities after traversing 5377

structures A and B. 5378

image contrast: The ability of a film (or other image receptor) to translate subject contrast to 5379

differences in the resulting image. Image contrast depends on both image receptor 5380

characteristics and film or computer processing. 5381


250

cycles per millimeter (c mm–1): The SI unit for spatial frequency often used to specify 5382

resolution of an imaging system. Each cycle consists of a light bar and a dark bar. Similar to 5383

line pairs per millimeter (lp mm–1) in both definition and numeric value. 5384

craniofacial: Of or involving both the cranium and the face. 5385

CT dose index (CTDI): A standardized measure of radiation dose output of a CT scanner which 5386

allows the user to compare radiation output of different CT scanners. CTDI is not a dose but 5387

rather a dose index. 5388

dental assistant: A member of the dental office staff whose principal duty is chair-side 5389

assistance of the dentist in delivery of care. The assistant, properly trained, may be 5390

credentialed for exposure of dental radiographs. 5391

dental caries: Technical term for tooth decay, sometimes referred to as “caries”. 5392

dental hygienist: A member of the dental office staff whose principal duty is performing oral 5393

prophylaxis and related procedures; in the United States, a graduate of an accredited 5394

educational program in dental hygiene and registered in the state or political jurisdiction in 5395

which the practice is located. The dental hygiene curriculum includes training in radiography 5396

and the hygienist is credentialed to expose dental radiographs. 5397

dental radiographic technologist: An individual who is trained and skilled in, and credentialed 5398

for, performing both routine and specialized radiographic examinations of the dentofacial 5399

region. 5400

dentist: A graduate of an accredited dental institution with a degree of Doctor of Dental Surgery 5401

(D.D.S.) or Doctor of Dental Medicine (D.M.D.), or equivalent. 5402

deterministic effect (tissue reaction): Effects that occur in all individuals who receive greater 5403

than the threshold dose and for which the severity of the effect varies with the dose. 5404

detriment: The overall risk of radiation-induced health outcomes, including fatal and nonfatal 5405

cancer, genetic effects, and loss of life span from cancer and hereditary disease, weighted for 5406

severity and time of expression of the harmful effect, and averaged over both sexes and all 5407

ages in the population of interest (i.e., general or working population). 5408

diagnostic source assembly: A diagnostic source housing (x-ray tube housing) assembly with a 5409

beam-limiting device attached. 5410

diagnostic reference level: A radiation dose level that, when consistently exceeded, elicits 5411

investigation of the reasons for the higher doses and subsequent efforts to improve dose 5412


251

management. A process known as optimization is used to assure that the clinical image 5413

quality is adequate for the clinical task and that the patient doses are appropriate. 5414

digital radiography: A diagnostic procedure using an appropriate radiation source and imaging 5415

system that collects, processes, stores, recalls and presents image information in a digital 5416

array rather than on film. 5417

direct digital radiography (DR): A radiographic technique in which an image is captured by a 5418

solid-state receptor and converted into a digital image. 5419

direct exposure film: Film which is exposed directly by x rays without the use of intensifying 5420

screens to produce a radiographic film image. 5421

display: An electronic device for viewing digital images. 5422

dose: (see absorbed dose). Often used generically in place of a specific quantity, such as 5423

equivalent dose. 5424

dose-area product (DAP): The product of the entrance skin dose and the cross-sectional area of 5425

the x-ray beam. DAP is also known as kerma area product (PKA). 5426

dose and dose rate effectiveness factor (DDREF): A judged factor by which the radiation 5427

effect, per unit of dose, caused by a given high or moderate dose of radiation received at high 5428

dose rates is modified when doses are low or are received at low dose rates. 5429

dose limit (annual): The maximum effective dose an individual may be permitted in any year 5430

from a given category of sources (e.g., the occupational dose limit). 5431

dosimetry: The science or technique of determining radiation dose. 5432

dosimeter: Dose measuring device (see also personal dosimeter and area dosimeter). 5433

E-F-speed film: A direct exposure dental imaging film that is an E-speed film when hand 5434

processed and an F-speed film when machine processed. The designation of E/F-speed film 5435

is also used. 5436

effective dose (E): The sum over specified organs and tissues of the products of the equivalent 5437

dose in an organ or tissue (HT) and the tissue weighting factor for that organ or tissue (wT): 5438

5439

(G.1) 5440

5441

E wTHTT=


252

entrance air kerma (or entrance skin exposure): Air kerma (or exposure) measured free-in-air 5442

at the location of the entry surface of an irradiated person or phantom in the absence of the 5443

person or phantom. 5444

equipment performance evaluation: This evaluation is carried out by the qualified expert 5445

initially to assure equipment meets purchase specifications and then on a periodic basis to 5446

assure that the image quality and patient radiation doses remain at the same level. 5447

equivalent dose (HT): The mean absorbed dose in a tissue or organ modified by the radiation 5448

weighting factor (wR) for the type and energy of radiation. The equivalent dose in tissue T is 5449

given by the expression. 5450

5451

(G.2) 5452

5453

where DT,R is the mean absorbed dose in the tissue or organ T due to radiation type R. The SI 5454

unit of equivalent dose is the J kg–1 with the special name sievert (Sv). 1 Sv = 1 J kg–1 5455

exposure: A measure of the ionization produced in air by x or gamma radiation. The unit of 5456

exposure is coulomb per kilogram (C kg–1) with the special name roentgen (R). Air kerma is 5457

often used in place of exposure. An exposure of 1 R corresponds to an air kerma of 5458

8.76 mGy (see kerma, gray, roentgen). 5459

field size: The geometrical projection of the x-ray beam on a plane perpendicular to the central 5460

ray of the distal end of the limiting diaphragm, as seen from the center of the front surface of 5461

the source. 5462

film: A thin, transparent sheet of polyester or similar material coated on one or both sides with 5463

an emulsion sensitive to radiation and light. 5464

direct exposure film: Film that is highly sensitive to the direct action of x rays rather than in 5465

combination with an intensifying screen. 5466

screen-film system: Film whose light spectral absorption characteristics are matched to the light 5467

emission characteristics of the intensifying screens; film for screen-film imaging is not 5468

designed for use as direct exposure film as it absorbs only a limited amount of x rays. 5469

film speed: For intraoral films, film speed is expressed as the reciprocal of the exposure (i.e., 5470

R–1) necessary to produce a density of one above base plus fog. 5471

D-Speed film: Direct exposure film with a speed range of 12 to 24 R–1. 5472

H wRDT,RR=


253

E-speed film: Direct exposure film with a speed range of 24 to 48 R–1. 5473

F-speed film: Direct exposure film with a speed range of 48 to 96 R–1. Faster films need less 5474

exposure (i.e., a larger value of R–1) to produce the same film density (e.g., F-speed film 5475

is faster than E-speed film). For screen-film systems, film speed is expressed in 5476

combination with an intensifying screen. 5477

filter; filtration: Material in the useful beam that absorbs, preferentially, the less penetrating 5478

radiation, i.e., the radiation that will be absorbed by the body and not contribute to forming 5479

the image. The total filtration consists of inherent and added filters. 5480

inherent filtration: The filtration permanently in the useful beam; it includes the window of the 5481

x-ray tube and any permanent enclosure for the tube or source. 5482

added filtration: Filter in addition to the inherent filtration. 5483

fluoroscopy: The process of producing a real-time image using x rays. The machine used for 5484

visualization, in which the dynamic image appears in real time on a display screen (usually 5485

video) is a fluoroscope. The fluoroscope can also produce a static record of an image formed 5486

on the output phosphor of an image intensifier. The image intensifier is an x-ray image 5487

receptor that increases the brightness of a fluoroscopic image by electronic amplification and 5488

image minification. 5489

focal spot, effective: The apparent size of the radiation source region in a source assembly when 5490

viewed from the central axis of the useful radiation beam. 5491

fog: A darkening of the whole or part of a radiograph by sources other than the radiation of the 5492

primary beam to which the film was exposed. This can be due to chemicals in the processing 5493

solutions, light, or nonprimary beam (scattered) radiation. 5494

geometric distortion: Distortion of the recorded image due to the combined optical effect of 5495

finite size of the focal spot and geometric separation of the anatomic area of interest from the 5496

image receptor and the focal spot. 5497

genetic effects: Changes in reproductive cells that may result in detriment to offspring. 5498

gray (Gy): The special name given to the SI unit of absorbed dose and kerma. 1 Gy = 1 J kg–1. 5499

grid: A device used to reduce scattered radiation reaching an image receptor during the making 5500

of a radiograph. It consists of a series of narrow (usually lead) strips closely spaced on their 5501

edges, separated by spacers of low density material. 5502

half-value layer: Thickness of a specified substance that, when introduced into the path of a 5503

given beam of radiation, reduces the air-kerma rate (or exposure rate) by one-half. 5504


254

hazardous chemical: Any chemical that is a physical hazard or a health hazard as defined by 5505

the Occupational Safety and Health Administration (OSHA, 1994a). 5506

HERCA: The Heads of European Radiological Protection Competent Authorities is a voluntary 5507

association of radiation protection program representatives. The association addresses 5508

common issues and proposes practical solutions for these issues. Similar to the CRCPD in 5509

the United States. 5510

image receptor: A system for deriving a diagnostically usable image from the x rays transmitted 5511

through the patient. Examples include direct exposure x-ray film, screen-film system, 5512

photostimulable storage phosphor, and solid state receptor. 5513

inherent filtration: (see filter). 5514

intraoral radiograph: Radiograph produced on an image receptor placed intraorally and 5515

lingually or palatally to the teeth. 5516

in utero. In the uterus; refers to a fetus or embryo. 5517

inverse square law: A physical law stating that in the absence of intervening absorbers, the 5518

intensity of radiation from a point source is inversely proportional to the square of the 5519

distance from the source. As an example, a point source that produces 10 Gy h–1 at 1 m will 5520

produce 2.5 Gy h–1 at 2 m. 5521

ionization chamber: A device for detection of ionizing radiation or for measurement of 5522

radiation exposure and exposure rate. 5523

ionizing radiation: Any electromagnetic or particulate radiation capable of producing ions, 5524

directly or indirectly, by interaction with matter. Examples are x-ray photons, charged atomic 5525

particles, and other ions, and neutrons. 5526

kerma (K) (kinetic energy released per unit mass): The sum of the initial kinetic energies of 5527

all the charged particles liberated by uncharged particles per unit mass of a specified 5528

material. The SI unit for kerma is J kg–1 with the special name gray (Gy). 1 Gy = 1 J kg–1. 5529

Kerma can be quoted for any specified material at a point in free space or in an absorbing 5530

medium (see air kerma). 5531

kerma area product (KAP): See dose area product. 5532

kilovolt (kV): A unit of electrical potential difference equal to 1,000 volts. 5533

kilovolt peak (kVp): (also see operating potential). The peak-to-peak value in kilovolts of the 5534

potential difference of a pulsating potential generator. When only one-half of the waveform 5535

is used, the value refers to the useful half of the cycle. In this Report, the potential formed by 5536


255

a constant-potential generator is also expressed as kilovoltage. The operating potential of x-5537

ray equipment is expressed in terms of kilovoltage peak (kVp). 5538

latent image: The invisible change produced in an x-ray or photographic film emulsion by the 5539

action of x radiation or light, from which the visible image is subsequently developed and 5540

fixed chemically; or the change produced in a photostimulable storage phosphor and 5541

recovered by scanning with a laser. 5542

latitude: The range between the minimum and maximum radiation exposures to an image 5543

receptor that yield diagnostic images of structures. 5544

lead apron: An apron made with lead or other radiation absorbing material used to reduce 5545

radiation exposure. 5546

leakage radiation: (see radiation). 5547

linear nonthreshold (LNT): The hypothesis for radiation induction of cancer that states that no 5548

dose is completely without risk of such detriment, and that the relationship between 5549

increasing dose and increasing cancer incidence is linear through zero dose. 5550

luminance: A photometric measure of the luminous intensity per unit area of light travelling in a 5551

given direction. The SI unit for luminance is the candela m–2, sometimes referred to as a nit. 5552

magnification (in medical x-ray imaging): An imaging procedure carried out with 5553

magnification usually produced by purposeful introduction of distance between the subject 5554

and the image receptor. 5555

milliampere (mA): Electrically, 1 × 10–3 ampere. In radiography, the current flow from the 5556

cathode to the anode of the x-ray tube that, in turn, regulates the intensity of radiation 5557

emitted by the x-ray tube, thus directly influencing radiographic exposure. 5558

milliampere-minutes (mA min): The product of the x-ray tube operating current and exposure 5559

time, in minutes. 5560

milliampere-seconds (mAs): The product of the x-ray tube operating current and exposure time, 5561

in seconds. 5562

monitor: To determine the level of ionizing radiation or radioactive contamination in a given 5563

region or a device used for this purpose. Also, a device used for viewing x-ray images for 5564

diagnostic purposes. 5565

natural background radiation: Radiation originating in natural sources. e.g., cosmic rays, 5566

naturally occurring radioactive minerals, naturally occurring radioactive 14C and 40K in the 5567

body. 5568


256

noise: The presence of random fluctuations in image intensity that do not relate to the subject 5569

being imaged. Noise is related to both speed and resolution pf the image receptor. Generally, 5570

faster systems have greater noise. Noise can also be caused by physical factors in the 5571

imaging system, e.g., contact with rollers in film processing or interference with image 5572

capture by intervening materials. 5573

occlusal radiograph: An intraoral radiograph made with the image receptor placed between the 5574

occlusal surfaces of the teeth, parallel to the occlusal plane, with the x-ray beam directed 5575

caudad or cephalad. 5576

occupancy factor (T): The factor by which the workload should be multiplied to correct for the 5577

degree of occupancy (by any one person) of the area in question while the source is in the 5578

“ON” condition and emitting radiation. This multiplication is carried out for radiation 5579

protection purposes to determine compliance with shielding design goals. 5580

occupational exposure: Exposures to individuals that are incurred in the workplace as a result 5581

of situations that can reasonably be regarded as being the responsibility of management. 5582

Exposures associated with medical diagnosis or treatment for the individual are excluded. 5583

operating potential: (also see kilovolt peak). The potential difference between the anode and 5584

cathode of an x-ray tube. 5585

operator: Any individual who personally utilizes or manipulates a source of radiation. 5586

optimization. A process through which image quality and patient radiation exposure are 5587

balanced. The goal is to assure image quality sufficient for diagnostic purposes while 5588

minimizing the radiation dose to the patient. 5589

oral and maxillofacial radiology: The dental specialty that deals with the production and 5590

interpretation of images of dentomaxillofacial structures, practiced by a dental specialist who 5591

has undergone additional training in the use of imaging procedures for diagnosis and 5592

treatment of diseases, injuries, and abnormalities of the orofacial structures. In general, the 5593

individual should be credentialed by either the American Board of Oral and Maxillofacial 5594

Radiology or a comparable specialty board, or be eligible to sit for credentialing by such a 5595

board. 5596

orofacial: Relating to the mouth and face. 5597

orthodontic treatment: Dental treatment that corrects misalignment of the teeth and jaws. 5598


257

panoramic radiography (pantomography): A method of radiography by which continuous 5599

curved surface tomograms of the maxillary and mandibular dental arches and their associated 5600

structures may be obtained. 5601

periapical radiograph: An intraoral radiograph that demonstrates crowns and roots of teeth and 5602

the surrounding alveolar bone structures. 5603

periodontal disease: An inflammatory process of the hard and soft tissues of the marginal 5604

periodontal structures that may destroy alveolar bone and result in tooth loss. 5605

personal dosimeter: A small radiation receptor that is worn by an individual and measures their 5606

exposure to radiation. Common personal dosimeters contain film, thermoluminescent or 5607

optically-stimulated luminescent materials, or an electronic sensor as the radiation detection 5608

device. 5609

phantom: An object used to simulate the absorption and scatter characteristics of the patient’s 5610

body for radiation or image quality measurement purposes. 5611

photon: A quantum of electromagnetic radiation. 5612

photostimulable storage phosphor (PSP) plate: The PSP plate is an image receptor which 5613

consists of a thin imaging plate encapsulated in a protective, light-proof cover. The receptor 5614

is pliable. Once the x-ray exposure is made, the plate is scanned (or read) with a laser. 5615

During this scanning light is emitted in proportion to the x-ray exposure of the receptor 5616

surface. The amount of light is converted into pixel intensity values. This image is then 5617

stored as a digital image for diagnostic purposes. 5618

pixel: A two-dimensional picture element in a digital image. 5619

position-indicating device (PID) (cone): An open-ended device on a dental x-ray machine (in 5620

the shape of a cylinder) designed to indicate the direction of the central ray and to serve as a 5621

guide in establishing a desired source-to-image receptor distance. Provision for beam 5622

collimation and added filtration can be incorporated into the construction of the device. 5623

short cone: An open ended cylinder that establishes a source-to-image receptor distance of ~20 5624

cm. 5625

long cone. An open ended cylinder that establishes a source-to-image receptor distance of ~40 5626

cm. 5627

protective apron: An apron made of radiation absorbing material(s), used to reduce radiation 5628

exposure. 5629


258

protective barrier: A barrier of radiation absorbing material(s) used to reduce radiation 5630

exposure. 5631

primary protective barrier: A protective barrier used to attenuate the useful beam for radiation 5632

protection purposes. 5633

secondary protective barrier: A barrier sufficient to attenuate scattered and leakage radiation 5634

for radiation protection purposes. 5635

qualified expert: As used in this Report, a medical physicist or medical health physicist, with 5636

experience in dental imaging, who is competent to design radiation shielding in dental x-ray 5637

facilities, and to advise the staff regarding other radiation protection needs of dental x-ray 5638

installations. The qualified expert is also competent to evaluate image quality and measure 5639

patient radiation doses. The qualified expert is a person who is certified by the American 5640

Board of Radiology, American Board of Medical Physicists, American Board of Health 5641

Physics, or Canadian College of Physicists in Medicine. 5642

quality assurance (QA): The mechanisms to ensure continuously optimal functioning of both 5643

technical and operational aspects of radiologic procedures to produce maximal diagnostic 5644

information while minimizing patient radiation exposure. A quality assurance program also 5645

sets the qualifications and continuing education of staff. 5646

quality control (QC). The technical part of the quality assurance program which provides 5647

physical measurements of imaging functions, e.g., film processor QC to monitor chemical 5648

activity or periodic checks of the quality of digital images by the qualified expert. 5649

rad: The previous name for the unit of absorbed dose. 1 rad = J kg–1. In the SI system of units, it 5650

is replaced by the gray (Gy). 1 Gy = 100 rad. 5651

radiation (ionizing): Electromagnetic radiation (x or gamma rays) or particulate radiation (alpha 5652

particles, beta particles, electrons, positrons, protons, neutrons, and heavy charged particles) 5653

capable of producing ions by direct or secondary processes in passage through matter. 5654

leakage radiation: All radiation coming from within the source assembly except for the useful 5655

beam. It includes the portion of the radiation coming directly from the source and not 5656

absorbed by the source assembly, as well as the scattered radiation produced within the 5657

source assembly. 5658

scattered radiation: Radiation that, during interaction with matter, is changed in direction. The 5659

change is usually accompanied by a decrease in energy. For purposes of radiation protection, 5660


259

scattered radiation is assumed to come primarily from interactions of primary radiation with 5661

tissues of the patient. 5662

useful beam: The radiation that passes through the opening in the beam-limiting device that is 5663

used for imaging. 5664

radiation biology: That branch of science dealing with radiation effects on biological systems. 5665

radiation protection survey: An evaluation of the radiation protection in and around an 5666

installation that includes radiation measurements, inspections, evaluations and 5667

recommendations. 5668

radiation weighting factor (wR): The factor by which the absorbed dose in a tissue or organ is 5669

modified to account for the type and energy of radiation in determining the probability of 5670

stochastic effects. For diagnostic x rays the radiation weighting factor is assigned the value 5671

of one. 5672

radiograph: A film or other record produced by the action of x rays on a sensitized surface. 5673

radiography: The production of images on film or other record by the action of x rays 5674

transmitted through the patient. 5675

radiology: That branch of healing arts and sciences that deals with the use of images in the 5676

diagnosis and treatment of disease. 5677

rare earth: Commonly used to refer to intensifying screens that contain one or more of the rare-5678

earth elements and that make use of the absorption and conversion features of these elements 5679

in x-ray imaging. 5680

receptor: Any device that absorbs a portion of the incident radiation energy 5681

and converts that portion into another form of energy which can be more easily used to produce 5682

desired results (e.g., production of an image) (also see image receptor). 5683

receptor holding device: A device containing intraoral and extraoral components that allows for 5684

the positioning and stabilization of the image receptor within the mouth and which extends 5685

outside of the mouth to aid in the alignment of the position-indicating device of the x-ray 5686

tube head. 5687

relative risk: The ratio of the risk of a given disease in those exposed to the risk of that disease 5688

in those not exposed. 5689

excess relative risk: Relative risk minus one (i.e., the fractional increase in incidence in the 5690

irradiated population). 5691


260

rem: The previous name for the unit numerically equal to the absorbed dose (D) in rad, modified 5692

by a quality factor (Q). 1 rem =0.01 J kg–1. In the SI system of units, it is replaced by the 5693

sievert (Sv), which is numerically equal to the absorbed dose (D) in gray modified by a 5694

radiation weighting factor (wR). 1 Sv = 100 rem. 5695

resolution: In the context of an image system, the output of which is finally viewed by the eye, 5696

it refers to the smallest size or highest spatial frequency of an object of given contrast that is 5697

just perceptible. The intrinsic resolution of an imaging system is measured in cycles per 5698

millimeter (c mm–1) the SI unit. Previously, line pairs per millimeter (lp mm–1) The 5699

resolution actually achieved when imaging lower contrast objects is normally much less, and 5700

depends upon many variables such as subject contrast levels and noise of the overall imaging 5701

system. 5702

roentgen (R): The previous name for exposure, which is a specific quantity of ionization 5703

(electrons) produced by the absorption of x- or gamma-radiation energy in a specified mass 5704

of air under standard conditions. 1 R = 2.58 × 10–4 coulombs per kilogram 5705

(C kg–1). 5706

safelight: Special lighting used in a darkroom that permits film to be transferred from cassette to 5707

processor without fogging. 5708

scatter: Deflection of radiation interacting with matter, causing change of direction of subatomic 5709

particles or photons, attenuation of the radiation beam, and usually some absorption of 5710

energy. 5711

scattered radiation: (see radiation). 5712

screen-film system. (see entry under film) 5713

secondary protective barrier: (see protective barrier). 5714

sharpness (image): (see resolution). 5715

shielding design goals (P): Practical radiation levels, measured at a reference point beyond a 5716

protective barrier, that result in the respective annual effective dose limit for workers or the 5717

general public not being exceeded, when combined with conservatively safe assumptions in 5718

the structural shielding design calculations. For low-LET radiation, the quantity air kerma is 5719

used. P can be expressed as an annual or weekly value (e.g., mGy week–1 or mGy y–1 air 5720

kerma). 5721

sievert (Sv): The name for the SI unit of dose equivalent (H), equivalent dose (HT) and effective 5722

dose (E). 1 Sv = 1 J kg–1. 5723


261

source assembly: (see diagnostic source assembly). 5724

source-to-image receptor distance. The distance, measured along the central ray, from the 5725

center of the x-ray focal spot to the surface of the image receptor. 5726

source-to-skin distance. The distance, measured along the central ray, from the center of the x-5727

ray focal spot to the skin of the patient. 5728

spatial resolution (see resolution). 5729

speed: (also see film speed). As applied to an image receptor, an index of the relative exposure 5730

required to produce an image of acceptable quality; faster image receptors need less 5731

exposure. 5732

stepwede: A device consisting of increments of an absorber through which a radiographic 5733

exposure is made on film to permit determination of the amounts of radiation reaching the 5734

film by measurements of film density. 5735

stochastic effects: Effects, the probability of which, rather than their severity, is a function of 5736

radiation dose, implying the absence of a threshold. (More generally, stochastic means 5737

random in nature). 5738

structured display: A display of digital images following a predefined template placing the 5739

images on a computer monitor in a standardized format. There are structured displays for 5740

different studies, e.g., full mouth series, or cephalometric series. 5741

tissue reactions: (see deterministic effects). 5742

tissue weighting factor (wT): The factor by which the equivalent dose in tissue or organ T is 5743

weighted, and which represents the relative contribution of that organ or tissue to the total 5744

detriment due to stochastic effects resulting from uniform irradiation of the whole body. 5745

tomography: A special technique to show in detail images of structures lying in a 5746

predetermined plane of tissue, while blurring or eliminating detail in images of structures in 5747

other planes. 5748

use factor (U): Fraction of the workload during which the useful beam is directed at the barrier 5749

under consideration. 5750

useful beam: (see radiation). 5751

user: Dentists, physicians, and others responsible for the radiation exposure of patients. 5752

waveform: An expression of the temporal variation of the operating potential applied to the x-5753

ray tube in the course of an exposure. 5754

single-phase: Produced by conventional alternating current line current. 5755


262

half-wave rectified: Producing a single 1/120 s pulse of x rays during each 1/60 s alternating 5756

current cycle. 5757

full-wave rectified: Producing two 1/120 s pulses of x rays during each 1/60 s alternating 5758

current cycle. 5759

three-phase: Produced by three-phase, full-wave rectified current, providing 12 overlapping 5760

1/120 s pulses during each 1/60 s alternating current cycle. 5761

constant potential: Produced by electronic manipulation of alternating line current to provide 5762

constant tube voltage and a beam energy spectrum that varies little or not at all during 5763

exposure. 5764

workload (W): The degree of use of a radiation source. For the dental x-ray machines covered 5765

in this Report, the workload is expressed in milliampere-minutes per week (mA min week–1). 5766

x rays: Electromagnetic radiation that is produced by high-energy electrons passing close to a 5767

nucleus of a high atomic number element such as when impinging on a metal target in an x-5768

ray machine. 5769

5770


263

Reference 5771

5772

AAE/AAOMR (2011). American Association of Endodontists/American Academy of Oral and 5773

Maxillofacial Radiology. “Use of cone-beam computed tomography in endodontics. Joint position 5774

statement of the American Association of Endodontists and the American Academy of Oral and 5775

Maxillofacial Radiology,” Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 111(2), 234–237. 5776

AAE/AAOMR (2015). American Association of Endodontists/American Academy of Oral and 5777

Maxillofacial Radiography. ”AAE and AAOMR joint position statement: Use of Cone Beam 5778

Computed Tomography in Endodontics 2015 update”., Oral Surg. Oral Med. Oral Pathol. Oral 5779

Radiol. 120(4), 508–512. 5780

AAOMR (2008). Carter L, Farman AG, Geist J, Scarfe WC, Angelopoulos C, Nair MK, Hildebolt CF, 5781

Tyndall D, Shrout M, American Academy of Oral and Maxillofacial Radiology. American Academy 5782

of Oral and Maxillofacial Radiology executive opinion statement on performing and interpreting 5783

diagnostic cone beam computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 5784

106(4):561–562. 5785

AAOMR (2013). American Academy of Oral and Maxillofacial Radiology. “Clinical recommendations 5786

regarding use of cone beam computed tomography in orthodontic treatment. Position statement by the 5787

American Academy of Oral and Maxillofacial Radiology,” Oral Surg. Oral Med. Oral Pathol. Oral 5788

Radiol. 116(2), 238–257. 5789

AAPM (2012). American Association of Physicists in Medicine. AAPM position statement on radiation 5790

risks from medical imaging proceduresPP 25-A. 5791

http://www.aapm.org/org/policies/details.asp?Id=318&type=PP 5792

AAPM (2015). American Association of Physicists in Medicine. Acceptance Testing and Quality Control 5793

of Dental Imaging Equipment (American Association of Physicists in Medicine, College Park, 5794

Maryland). In Press. 5795

ADA (2007). American Dental Association. The 2005–06 Survey of Dental Services Rendered 5796

(American Dental Association, Chicago). 5797

ADA (2012). American Dental Association. “The use of cone-beam computed tomography in dentistry: 5798

An advisory statement from the American Dental Association Council on Scientific Affairs,” J. Am. 5799

Dent. Assoc. 143(8), 899–902. 5800

ALEXIOU, K., STAMATAKIS, H. and TSIKLAKIS, K. (2009). “Evaluation of the severity of 5801

temporomandibular joint osteoarthritic changes related to age using cone beam computed 5802

tomography,” Dentomaxillofac. Radiol. 38(3),141–147. 5803


264

ALKURT, M.T., PEKER, I., BALA, O. and ALTUNKAYNAK, B. (2007). “In vitro comparison of four 5804

different dental x-ray films and direct digital radiography for proximal caries detection,” Oper. Dent. 5805

32(5), 504–509. 5806

ALMOG, D.M. and SANCHEZ, R. (1999). “Correlation between planned prosthetic and residual bone 5807

trajectories in dental implants,” J. Prosthet. Dent. 81(5), 562–567. 5808

AL-OKSHI, A., NILSSON, M., PETERSSON, A., WIESE, M. and LINDH, C. (2013). “Using 5809

GafChromic film to estimate the effective dose from dental cone beam CT and panoramic 5810

radiography,” Dentomaxillofac. Radiol. 42(7), 20120343. 5811

ALSUFYANI, N.A., AL-SALEH, M.A. and MAJOR, P.W. (2013). “CBCT assessment of upper airway 5812

changes and treatment outcomes of obstructive sleep apnoea: A systematic review,” Sleep Breath. 5813

17(3) 911–923. 5814

ANISSI, H.D. and GEIBEL, M.A. (2014). “Intraoral radiology in general dental practices – a comparison 5815

of digital and film-based x-ray systems with regard to radiation protection and dose reduction,” Rofo. 5816

186(8), 762–767. 5817

BECKER, A., CHAUSHU, S. and CASAP-CASPI, N. (2010).“Cone-beam computed tomography and 5818

the orthosurgical management of impacted teeth,” J. Am. Dent. Assoc. 141(Suppl 3), 14S–18S. 5819

BENAVIDES, E., RIOS, H.F., GANZ, S.D., AN, C.H., RESNIK, R., REARDON, G.T., FELDMAN, 5820

S.J., MAH, J.K., HATCHER, D., KIM, M.J., SOHN, D.S., PALTI, A., PEREL, M.L., JUDY, K.W., 5821

MISCH, C.E. and WANG, H.L. (2012). “Use of cone beam computed tomography in implant 5822

dentistry: The International Congress of Oral Implantologists consensus report,” Implant Dent. 21(2), 5823

78–86. 5824

BERKHOUT, W.E., SANDERINK, G.C. and VAN DER STELT, P.F. (2003). “Does digital radiography 5825

increase the number of intraoral radiographs? A questionnaire study of Dutch dental practices,” 5826

Dentomaxillofac. Radiol. 32(2), 124–127 5827

BERNSTEIN, D.I., CLARK, S.J., SCHEETZ, J.P., FARMAN, A.G. and ROSENSON, B. (2003). 5828

“Perceived quality of radiographic images after rapid processing of D- and F-speed direct-exposure 5829

intraoral x-ray films,” Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 96(4), 486–491. 5830

BOICE, J.D., JR., MORIN, M.M., GLASS, A.G., FRIEDMAN, G.D., STOVALL, M., HOOVER, R.N. 5831

and FRAUMENI, J.F., JR. (1991). “Diagnostic x-ray procedures and risk of leukemia, lymphoma, 5832

and multiple myeloma,” J. Am. Med. Assoc. 265(10), 1290–1294. 5833

BRENNER, D.J., and ELLISTON, C.D. (2004). “Estimated radiation risks potentially associated with 5834

full-body CT screening,” Radiology 232(3), 735–738. 5835

BRENNER, D.J. and HALL, E.J. (2007). “Computed tomography — an increasing source of radiation 5836

exposure,” N. Eng. J. Med. 357(22), 2277–2284. 5837


265

BRENNER, D.J., ELLISTON, C.D., HALL, E.J. and BERDON, W.E. (2001). “Estimated risks of 5838

radiation-induced fatal cancer from pediatric CT,” Am. J. Roentgenol. 176(2), 289–296. 5839

BUDOWSKY, J., PIRO, J.D., ZEGARELLI, E.V., KUTSCHER, A.H. and BARNETT, A. (1956). 5840

“Radiation exposure to the head and abdomen during oral roentgenography,” J. Am. Dent. Assoc. 5841

52(5), 555–559. 5842

BUSHBERG, J.T., SEIBERT, J.A., LEIDHOLDT, E.M.,JR. AND BOONE, J.M. (2012). The Essential 5843

Physics of Medical Imaging, 3rd ed. (Lippincott Williams and Wilkins, Philadelphia). 5844

CAKLI, H., CINGI, C., AY, Y., OGHAN, F., OZER, T. and KAYA, E. (2012). “Use of cone beam 5845

computed tomography in otolaryngologic treatments,” Eur. Arch. Otorhinolaryngeal. 269(3), 711–5846

720. 5847

CEDERBURG, R.A., FREDERIKSEN, N.L., BENSON, B.W. and SOKOLOWSKI, T.W. (1997). 5848

“Effect of the geometry of the intraoral position-indicating device on effective dose,” Oral Surg. Oral 5849

Med. Oral Pathol. Oral Radiol. Endod. 84(1), 101–109. 5850

CEVIDANES, L.H.S., BAILEY, L.J., TUCKER, S.F., STYNER, M.A., MOL, A., PHILLIPS, C.L., 5851

PROFFIT, W.R. and TURVEY, T. (2007). “Three-dimensional cone-beam computed tomography for 5852

assessment of mandibular changes after orthognathic surgery,” Am. J. Orthod. Dentofacial. Orthop. 5853

131(1), 44–50. 5854

CONOVER, G.L., HILDEBOLT, C.F. and ANTHONY, D. (1995). “Objective and subjective evaluations 5855

of Kodak Ektaspeed Plus dental x-ray film,” Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 5856

79(2), 246–250. 5857

CRCPD (2015). Conference of Radiation Control Program Directors. Suggested State Regulations for 5858

Control of Radiation, Part F – Medical Diagnostic and Interventional X-ray and Imaging Systems, 5859

http://www.crcpd.org/SSRCRs/Fpart_2015.pdf (accessed March 3, 2016) (Conference of Radiation 5860

Control Program Directors, Inc., Frankfort, Kentucky). 5861

D’AMBROSIO, J.A., SCHIFF, T.G., MCDAVID, W.D. and LANGLAND, O.E. (1986). “Diagnostic 5862

quality versus patient exposure with five panoramic screen-film combinations,” Oral Surg. Oral Med. 5863

Oral Pathol. 61(4), 409–411. 5864

DANFORTH, R.A., HERSCHAFT, E.E. and LEONOWICH, J.A. (2009). “Operator exposure to scatter 5865

radiation from a portable hand-held radiation emitting device (Aribex NOMAD) while making 915 5866

intraoral dental radiographs,” J. Forensic Sci. 54(2), 415–421. 5867

DAUER, L.T., BRANETS, I., STABULUS-SAVAGE, J., QUINN, B., MIODOWNIK, D., DAUER, 5868

Z.L., COLOSI, D., HERSHKOWITZ, D., GOREN, A. (2014). “Optimising radiographic bitewing 5869

examination to adult and juvenile patients through the use of anthropomorphic phantoms,” Radiat 5870

Prot Dosimetry. 158(1), 51–58. 5871


266

DAVIES, J., JOHNSON, B. and DRAGE, N. (2012). “Effective doses from cone beam CT investigation 5872

of the jaws,” Dentomaxillofac. Radiol. 41(1), 30–36. 5873

DAVIS, F.G., BOICE, J.D., JR., HRUBEC, Z. and MONSON, R.R. (1989). “Cancer mortality in a 5874

radiation-exposed cohort of Massachusetts tuberculosis patients,” Cancer Res. 49(21), 6130–6136. 5875

DE HAAN, R.A. and VAN AKEN, J. (1990). “Effective dose equivalent to the operator in intra-oral 5876

dental radiography,” Dentomaxillofac. Radiol. 19(3), 113–118. 5877

DIEHL, R., GRATT, B.M. and GOULD, R.G. (1986). “Radiographic quality control measurements 5878

comparing D-speed film, E-speed film, and xeroradiography,” Oral Surg. Oral Med. Oral Pathol. 5879

61(6), 635–640. 5880

DIXON, R.L. and SIMPKIN, D.J. (1998). “Primary shielding barriers for diagnostic x-ray facilities: A 5881

new model,” Health Phys. 74(2), 181–189. 5882

DOLL, R. and WAKEFORD, R. (1997). “Risk of childhood cancer from fetal irradiation,” Brit. J. Radiol. 5883

70, 130–139. 5884

DOS ANJOS PONTUAL, M.L., FREIRE, J.S.L., BARBOSA, J.M.N., FRAZAO, M.A.G., DOS ANJOS 5885

PONTUAL, A. and FONSECA DA SILVEIRA, M.M. (2012). “Evaluation of bone changes in the 5886

temporomandibular joint using cone beam CT,” Dentomaxillofac. Radiol. 41(1), 24–29. 5887

DOUPLE, E.B., MABUCHI, K., CULLINGS, H.M., PRESTON, D.L., KODAMA, K., SHIMIZU, Y., 5888

FUJIWARA, S. and SHORE, R.E. (2011). “Long-term radiation-related health effects in a unique 5889

human population: Lessons learned from the atomic bomb survivors of Hiroshima and Nagasaki,” 5890

Disaster Med. Public Health Prep. 5(0 1), S122–S133. (accessed September 28, 2015. 5891

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3907953/015). 5892

EADMFR (2009). European Academy of Dentomaxillofacial Radiology. Basic Principles for Use of 5893

Dental Cone Beam CT: Consensus Guidelines of the European Academy of Dental and Maxillofacial 5894

Radiology (European Academy of Dentomaxillofacial Radiology, University of Manchester, 5895

Manchester, United Kingdom). 5896

EBRAHIM, F., IABONI, D., KWON, T., SEKOULIDIS, J., CAULLEY, L. and ZAJACZKOWSKI, I. 5897

(2009). Cone Beam CT For Preoperative Dental Implant Site Assessment: An Evidence‐Based 5898

Review of the Literature, https://www.dentistry.utoronto.ca/system/files/z2eblreport-2009_0.pdf 5899

(accessed August 4, 2015) (University of Toronto Faculty of Dentistry, Toronto). 5900

EC (2012). European Commission. Cone Beam CT for Dental and Maxillofacial Radiology: Evidence 5901

Based Guidelines, Radiation Protection No. 172 (European Commission, Luxembourg). 5902

ERGÜN, S., GUNERI, P., ILGUY, D., ILGUY, M. and BOYACIOGLU, H. (2009). “How many times 5903

can we use a phosphor plate? A preliminary study,” Dentomaxillofac. Radiol. 38(1), 42–47. 5904


267

FARMAN, T.T. and FARMAN, A.G. (2000). “Evaluation of a new F speed dental x-ray film. The effect 5905

of processing solutions and a comparison with D and E speeds films,” Dentomaxillofac. Radiol. 5906

29(1), 41–45. 5907

FARMAN, A.G. and FARMAN, T.T. (2005). “A comparison of 18 different x-ray detectors currently 5908

used in dentistry,” Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 99(4), 485–489. 5909

FARMAN, A.G. and SCARFE, W.C. (2006). “Development of imaging selection criteria and procedures 5910

should precede cephalometric assessment with cone-beam computed tomography,” Am. J. Orthod. 5911

Dentofacial. Orthop. 130(2), 257–265. 5912

FARRIS, K. and SPELIC, D. (2015). Nationwide Evaluation of X-Ray Trends: Highlights of the 2014-15 5913

NEXT Dental Survey, Proceedings of the 47th National Conference on Radiation Control, August 5914

2015. CRCPD Publication E-15-4, 2015. 5915

FDA (2005). U.S. Food and Drug Administration. “21 CFR 1020.33(d)—Performance standards for 5916

ionizing radiation emitting products. Computed tomography (CT) equipment. Quality assurance,” 70 5917

FR 34042 (U.S. Government Printing Office, Washington). 5918

FDA (2012). U.S. Food and Drug Administration. Illegal Sale of Potentially Unsafe Hand-Held Dental 5919

X-Ray Units: FDA Safety Communication, http://www.fda.gov/Radiation-5920

EmittingProducts/RadiationSafety/AlertsandNotices/ucm291214.htm (accessed September 16, 2015) 5921

(U.S. Food and Drug Administration, Silver Spring, Maryland). 5922

FDA (2014). U.S. Food and Drug Administration. Dental Radiography: Doses and Film Speed, 5923

http://www.fda.gov/Radiation-EmittingProducts/RadiationSafety/NationwideEvaluationofX-5924

RayTrendsNEXT/ucm116524.htm (accessed September 16, 2015) (U.S. Food and Drug 5925

Administration, Silver Spring, Maryland). 5926

FDA (2015). U.S. Food and Drug Administration. “21 CFR Part 1020 -- Performance Standards for 5927

Ionizing Radiation Emitting Products. 5928

https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfCFR/CFRSearch.cfm?CFRPart=1020 (accessed 5929

September 22, 2015) (U.S. Food and Drug Administration, Silver Spring, Maryland). 5930

FDA/ADA (2015a). U.S. Food and Drug Administration/American Dental Association. Dental 5931

Radiographic Examinations: Recommendations for Patient Selection and Limiting Radiation 5932

Exposure, http://www.fda.gov/Radiation-5933

EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/MedicalX-5934

Rays/ucm116504.htm (accessed August 4, 2015) (U.S. Food and Drug Administration, Silver Spring, 5935

Maryland). 5936


268

FDA/ADA (2015b). U.S. Food and Drug Administration/American Dental Association. Chart: Guidelines 5937

for Prescribing Dental Radiographs, http.//www.fda.gov/Radiation-5938

EmittingProducts/RadiationEmittingProductsand Procedures/MedicalImaging/MedicalX-5939

Rays/ucm116506.htm (accessed August 4, 2015) (U.S. Food and Drug Administration, Silver Spring, 5940

Maryland). 5941

FLINT, D.J., PAUNOVICH, E., MOORE, W.S., WOFFORD, D.T. and HERMESCH, C.B. (1998). “A 5942

diagnostic comparison of panoramic and intraoral radiographs,” Oral Surg. Oral Med. Oral Pathol. 5943

Oral Radiol. Endod. 85(6), 731–735. 5944

FREEDMAN, M.L. and MATTESON, S.R. (1976). “A collimator for reduced radiation dose with 5945

improved visualization of soft tissues,” Radiology 118(1), 226–228. 5946

FREEMAN, J.P. and BRAND, J.W. (1994). “Radiation doses of commonly used dental radiographic 5947

surveys,” Oral Surg. Oral Med. Oral Pathol. 77(3), 285–289. 5948

GIBBS, S.J. (2000). “Effective dose equivalent and effective dose: Comparison for common projections 5949

in oral and maxillofacial radiology,” Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 90(4), 5950

538–545. 5951

GIBBS, S.J., PUJOL, A., JR., CHEN, T.S., CARLTON, J.C., DOSMANN, M.A., MALCOLM, A.W. 5952

and JAMES, A.E., JR. (1987). “Radiation doses to sensitive organs from intraoral dental 5953

radiography,” Dentomaxillofac. Radiol. 16(2), 67–77. 5954

GIBBS, S.J., PUJOL, A., JR., CHEN, T.S. and JAMES, A., JR. (1988). “Patient risk from intraoral dental 5955

radiography,” Dentomaxillofac. Radiol. 17(1), 15–23. 5956

GOREN, A.D., SCIUBBA, J.J., FRIEDMAN, R. and MALAMUD, H. (1989). “Survey of radiologic 5957

practices among dental practitioners,” Oral Surg. Oral Med. Oral Pathol. 67(4), 464–468. 5958

GOREN, A.D., BONVENTO, M., BIERNACKI, J. and COLOSI, D.C. (2008). “Radiation exposure with 5959

the NOMAD portable x-ray system,” Dentomaxillofac. Radiol. 37(2), 109–112. 5960

GRATT, B.M., WHITE, S.C., PACKARD, F.L. and PETERSSON, A.R. (1984). “An evaluation of rare-5961

earth imaging systems in panoramic radiography,” Oral Surg. Oral Med. Oral Pathol. 58(4), 475–482. 5962

GRAY, J.E. (1992). “Use of the SMPTE test pattern in picture archiving and communication systems,” J. 5963

Digit. Imaging 5(1), 54–58. 5964

GRAY, J.E., LISK, K.G., HADDICK, D.H., HARSHBARGER, J.H., OOSTERHOF, A. and 5965

SCHWENKER, R.S. (1985) “Test pattern for video displays and hard-copy cameras,” Radioilogy 5966

154(2), 519–527. 5967

GRAY, J.E., BAILEY, E. and LUDLOW, J.B. (2012). “Dental staff doses for hand-held dental intraoral 5968

x-ray units,” Health Phys. 102(2), 137–142. 5969


269

GRUNHEID, T., KOLBECK SCHIECK, J.R., PLISKA, B.T., AHMAD, M. and LARSON, B.E. (2012). 5970

“Dosimetry of a cone-beam computed tomography machine compared with a digital x-ray machine in 5971

orthodontic imaging,” Am. J. Orthod. Dentofacial Orthop. 141(4), 436–443. 5972

GULDNER, C., NINGO, A., VOIGT, J., DIOGO, I., HEINRICHS, J., WEBER, R., WILHELM, T. and 5973

FIEBICH, M. (2013). “Potential of dosage reduction in cone-beam-computed tomography (CBCT) 5974

for radiological diagnostics of the paranasal sinuses,” Eur. Arch Otorhinolaryngol. 270(4), 1307–5975

1315. 5976

HALL, E.J. and GIACCIA, A.J. (2011). Radiobiology for the Radiologist, 7th ed. (Lippincott, Williams 5977

and Wilkins, Philadelphia). 5978

HAN, G.S., CHENG, J.G., LI, G. and MA, X.C. (2013). “Shielding effect of thyroid collar for digital 5979

panoramic radiography,” Dentomaxillof. Radiol. 42(9), 20130265. 5980

HARRIS, D., HORNER, K., GRONDAHL, K., JACOBS, R., HELMROT, E., BENIC, G.I., 5981

BORNSTEIN, M.M., DAWOOD, A. and QUIRYNEN, M. (2012). “E.A.O. guidelines for the use of 5982

diagnostic imaging in implant dentistry 2011. A consensus workshop organized by the European 5983

Association for Osseointegration at the Medical University of Warsaw,” Clin. Oral Implants Res. 5984

23(11), 1243–1253. 5985

HART, D., HILLIER, M.C. and SHRIMPTON, P.C. (2012). Doses to Patients from Radiographic and 5986

Fluoroscopic X-Ray Imaging Procedures in the UK – 2010 Review, HPA-CRCE-034 (Health 5987

Protection Agency, London). 5988

http.//webarchive.nationalarchives.gov.uk/20140722091854/http.//www.hpa.org.uk/Publications/Radi5989

ation/CRCEScientificAndTechnicalReportSeries/ (accessed February 2, 2015). 5990

HERCA (2014). Heads of the European Radiological Protection Competent Authorities. Position 5991

Statement on Use of Handheld Portable Dental X-Ray Equipment, 5992

http://www.herca.org/uploaditems/documents/HERCA%20position%20statement%20on%20use%205993

of%20handheld%20portable%20dental%20x-ray%20equipment.pdf (accessed September 29, 2015). 5994

HILDRETH, N.G., SHORE, R.E., HEMPELMANN, L.H. and ROSENSTEIN, M. (1985). “Risk of 5995

extrathyroid tumors following radiation treatment in infancy for thymic enlargement,” Radiat. Res. 5996

102(3), 378–391. 5997

HINTZE, H., WENZEL, A. and JONES, C. (1994). “In vitro comparison of D- and E-speed film 5998

radiography, RVG, and Visualix digital radiography for the detection of enamel approximal and 5999

dentinal occlusal caries lesions,” Caries Res. 28(5), 363–367. 6000

HINTZE, H., CHRISTOFFERSEN, L. and WENZEL, A. (1996). “In vitro comparison of Kodak Ultra-6001

Speed, Ektaspeed, and Ektaspeed Plus, and Agfa M2 Comfort dental x-ray films for the detection of 6002

caries,” Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 81(2), 240–244. 6003


270

HOLROYD, J.R. (2011). “National reference doses for dental cephalometric radiography,” Brit. J. 6004

Radiol. 84(1008), 1121–1124. 6005

HOLROYD, J.R. (2013). Trends in Dental Radiography Equipment and Patient Dose in the UK and 6006

Republic of Ireland. A Review of Data Collected by the HPA Dental X-Ray Protection Services 6007

between 2008 and 2011 for Intra-Oral and Panoramic X-Ray Equipment, HPA-CRCE-043 (Public 6008

Health England, London). 6009

HORNER, K., O’MALLEY, L., TAYLOR, K. and GLENNY, A.M. (2015). “Guidelines for clinical use 6010

of CBCT: A review,” Dentomaxillofac. Radiol. 44(1), 201402225. 6011

HOWE, G.R. and MCLAUGHLIN. J. (1996). “Breast cancer mortality between 1950 and 1987 after 6012

exposure to fractionated moderate-dose-rate ionizing radiation in the Canadian fluoroscopy cohort 6013

study and a comparison with breast cancer mortality in the atomic bomb survivors study,” Radiat. 6014

Res. 145(6), 694–707. 6015

HPA (2010). Health Protection Agency. Guidance on the Safe Use of Dental Cone Beam CT (Computed 6016

Tomography) Equipment, HPA-CRCE-010, 6017

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/340159/HPA-CRCE-6018

010_for_website.pdf (accessed August 4, 2015) (Public Health England, London). 6019

HPA (2012). Health Protection Agency. Tianjie Dental ‘Falcon’ Hand Held X-Ray Set Imported from 6020

China: Summary of HPA Radiation Protection Assessment Results, 6021

http://www.fanc.fgov.be/GED/00000000/3500/3525.pdf (accessed October 20, 2015) (Public Health 6022

England, London). 6023

HPS (2016). Health Physics Society. 2015 Health Physics Society Symposium, 13–14 July 2015, Health 6024

Risks from Low Doses and Low Dose-Rates of Ionizing Radiation, Health Phys 110(3), 241–304. 6025

HSE (1998). Health and Safety Executive. Occupational Exposure to Ionizing Radiation 1990 –1996. 6026

Analysis of Doses Reported to the Health and Safety Executive’s Central Index of Dose Information 6027

(Her Majesty’s Stationery Office, Norwich, United Kingdom). 6028

HUDA, W. (2010). Review of Radiologic Physics, 3rd ed. (Lippincott Williams and Wilkins, Baltimore, 6029

Maryland). 6030

IAC (2015). Intersocietal Accreditation Commission. About the IAC, http://www.intersocietal.org/ 6031

(accessed September 12, 2015) (Intrsocietal Accreditation Commission, Ellicott City, Maryland). 6032

ICRP (1991). International Commission on Radiological Protection. 1990 Recommendations of the 6033

International Commission on Radiological Protection, ICRP Publication 60, Annals of the ICRP 6034

21(1-3) (Elsevier Science, New York). 6035

ICRP (2004). International Council on Radiation Protection and Measurements. Managing Patient Dose 6036

in Digital Radiology, ICRP Publication 93, Ann ICRP 34(1) (Sage Publications, Thousand Oaks, 6037

California). 6038


271

ICRP (2007a). International Commission on Radiological Protection. The 2007 Recommendations of the 6039

International Commission on Radiological Protection, ICRP Publication 103, Ann. ICRP 37(2–4) 6040

(Sage Publications, Thousand Oaks, California). 6041

ICRP (2007b). International Commission on Radiological Protection. Radiological Protection in 6042

Medicine, ICRP Publication 105, Ann. ICRP 37(6) (Sage Publications, Thousand Oaks, California). 6043

ICRP (2009). International Commission on Radiological Protection. Education and Training in 6044

Radiological Protection for Diagnostic and Interventional Procedures, ICRP Publication 113, Ann. 6045

ICRP 39(5) (Sage Publications, Thousand Oaks, California). 6046

ICRP (2011). International Commission on Radiological Protection. Statement on Tissue Reactions, ICRP 6047

ref 4825-3093-1464, www.icrp.org/docs/icrp%20statement%20on%20tissue%20reactions.pdf 6048

(accessed September 15, 2015) (International Commission on Radiological Protection, Ottawa, 6049

Ontario). 6050

ICRP (2012). International Commission on Radiological Protection. Statement on Tissue Reactions and 6051

Early and Late Effects of Radiation in Normal Tissues and Organs – Threshold Doses for Tissue 6052

Reactions in a Radiation Protection Context. Annals of the ICRP, 41:1-322. 6053

ICRU (1993). International Commission on Radiation Units and Measurements. Quantities and Units in 6054

Radiation Protection Dosimetry, ICRU Report 51 (International Commission on Radiation Units and 6055

Measurements, Bethesda, Maryland). 6056

ICRU (1998). International Commission on Radiation Units and Measurements. Fundamental Quantities 6057

and Units for Ionizing Radiation, ICRU Report 60 (International Commission on Radiation Units and 6058


IEC (2012). International Electrotechnical Commission. Medical Electrical Equipment - Part 2-65: 6060

Particular Requirements for the Basic Safety and Essential Performance of Dental Intra-Oral X-Ray 6061

Equipment, IEC 60601-2-65:2012 (International Electrotechnical Commission, Geneva). 6062

JACOB, P., RUHM, W., WALSH, L., BLETTNER, M., HAMMER, G. and ZEEB, H. (2009). “Is cancer 6063

risk of radiation workers higher than expected?,” Occup. Environ. Med. 66(12), 789–796. 6064

JADU, F., YAFFE, M.J. and LAM, E.W.N. (2010). “A comparative study of the effective radiation doses 6065

from cone beam computed tomography and plain radiography for sialography,” Dentomaxillofac. 6066

Radiol. 39(5), 257–263. 6067

JEONG, D.K., LEE, S.C., HUH, K.H., YI, W.J., HEO, M.S., LEE, S.S. and CHOI, S.C. (2012). 6068

“Comparison of effective dose for imaging of mandible between multi-receptor CT and cone-beam 6069

CT,” Imaging Sci. Dent. 42(2), 65–71. 6070

JOHNS, H.E. and CUNNINGHAM, J.R. (1983). The Physics of Radiology, 4th ed. (Charles C. Thomas, 6071

Springfield, Illinois). 6072


272

JOHNSON, B., LUDLOW, J.B., MAURIELLO, S.M. and PLATIN, E. (2014). “Intraoral radiographic 6073

imaging risk reduction with collimation and thyroid shielding,” Gen. Dent. 62(4), 34–40. 6074

JUNG, Y.H. and CHO, B.H. (2012). “Assessment of the relationship between the maxillary molars and 6075

adjacent structures using cone beam computed tomography,” Imaging Sci. Dent. 42(4), 219–224. 6076

KALLIO-PULKKINEN, S., HAAPEA, M., LIUKKONEN, E., HUUMONEN, S., TERVONEN, O. and 6077

NIEMINEN, M.T. (2014). “Comparison of consumer grade, tablet and 6MP-displays: Observer 6078

performance in detection of anatomical and pathological structures in panoramic radiographs,” Oral 6079

Surg. Oral Med. Oral Pathol. Oral Radiol. 118(1), 135–141. 6080

KAMBUROGLU, K., KOLSUZ, E., MURAT, S., YUKSEL, S. and OZEN, T. (2012). “Proximal caries 6081

detection accuracy using intraoral bitewing radiography, extraoral bitewing radiography and 6082

panoramic radiography,” Dentomaxillof. Radiol. 41(6), 450–459 6083

KAUGARS, G.E. and FATOUROS, P. (1982). “Clinical comparison of conventional and rare earth 6084

screen-film systems for cephalometric radiographs,” Oral Surg. Oral Med. Oral Pathol. 53(3), 322–6085

325. 6086

KIM, D.S., RASHSUREN, O. and KIM, E.K. (2014). “Conversion coefficients for the estimation of 6087

effective dose in cone-beam CT,” Imaging Sci. Dent. 44(1), 21–29. 6088

KITAGAWA, H., FARMAN, A.G., WAKOH, M., NISHIKAWA, K. and KUROYANAGI, K. (1995). 6089

“Objective and subjective assessments of Kodak Ektaspeed plus new dental x-ray film: A comparison 6090

with other conventional x-ray films,” Bull. Tokyo Dent. Coll. 36(2), 61–67. 6091

KUIJPERS, M.A.R., PAZERA, A., ADMIRAAL, R.J., BERGE, S.J., VISSINK, A. and PAZERA, P. 6092

(2014). “Incidental findings on cone beam computed tomography scans in cleft lip and palate 6093

patients,” Clin. Oral Investig. 18(4), 1237–1244. 6094

KUMAZAWA, S., NELSON, D.R. and RICHARDSON, A.C.B. (1984). Occupational Exposure to 6095

Ionizing Radiation in the United States: A Comprehensive Review for the Year 1980 and a Summary 6096

of Trends for the Years 1960–1985, EPA 520/1-84/005 (National Technical Information Service, 6097

Springfield, Virginia). 6098

KUTCHER, M.J., KALATHINGAL, S., LUDLOW, J.B., ABREU, M., JR. and PLATIN, E. (2006). 6099

“The effect of lighting conditions on caries interpretation with a laptop computer in a clinical 6100

setting,” Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 102(4), 537–543. 6101

LARA (2015). Department of Licensing and Regulatory Affairs, Michigan Occupational Safety and 6102

Health Administration. Patient Radiation Exposure Information, 6103

http://www.michigan.gov/lara/0,4601,7-154-11407_35791-46650--,00.html (accessed September 15, 6104

2015) (Department of Licensing and Regulatory Affairs, Michigan Occupational Safety and Health 6105

Administration, Lansing). 6106


273

LIBRIZZI, Z.T., TADINADA, A.S., VALIYAPARAMBIL, J.V., LURIE, A.G. and MALLYA, S.M. 6107

(2011). “Cone-beam computed tomography to detect erosions of the temporomandibular joint: Effect 6108

of field of view and voxel size on diagnostic efficacy and effective dose,” Am. J. Orthod. 6109

Dentofacial. Orthop. 140(1), e25–e30. 6110

LINET, M.S., SLOVIS, T.L., MILLER, D.L., KLEINERMAN, R., LEE, C., RAJARAMAN, P. and 6111

BERRINGTON DE GONZALEZ, A. (2012). “Cancer risks associated with external radiation from 6112

diagnostic imaging procedures,” CA Cancer J. Clin. 62(2), 75–100. 6113

LU, Y., LIU, Z., ZHANG, L., ZHOU, X., ZHENG, Q., DUAN, X., ZHENG, G., WANG, H. and 6114

HUANG, D. (2012). “Associations between maxillary sinus mucosal thickening and apical 6115

periodontitis using cone-beam computed tomography scanning: A retrospective study,” J. Endod. 6116

38(8), 1069–1074. 6117

LUDLOW, J.B. (2011). “A manufacturer's role in reducing the dose of cone beam computed tomography 6118

examinations: Effect of beam filtration,” Dentomaxillofac. Radiol. 40(2), 115–122. 6119

LUDLOW, J.B. (2012). “Comment on "effective dose range for dental cone beam computed tomography 6120

scanners,” Eur. J. Radiol. 81(12), 4219–4220. 6121

LUDLOW, J.B. and IVANOVIC, M. (2008). “Comparative dosimetry of dental CBCT devices and 64-6122

slice CT for oral and maxillofacial radiology,” Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 6123

106(1), 106–114. 6124

LUDLOW, J.B. and WALKER, C. (2013). “Assessment of phantom dosimetry and image quality of i-6125

CAT FLX cone-beam computed tomography,” Am. J. Orthod. Dentofacial. Orthop. 144(6), 802–817. 6126

LUDLOW, J.B., PLATIN, E., DELANO, E.O. and CLIFTON, L. (1997). “The efficacy of caries 6127

detection using three intraoral films under different processing conditions,” J. Am. Dent. Assoc. 6128

128(10), 1401–1408. 6129

LUDLOW, J.B., ABREU, M., JR. and MOL, A. (2001). “Performance of a new F-speed film for caries 6130

detection,” Dentomaxillofac. Radiol. 30(2), 110–113. 6131

LUDLOW, J.B., DAVIES-LUDLOW, L.E. and WHITE, S.C. (2008). “Patient risk related to common 6132

dental radiographic examinations: The impact of 2007 International Commission on Radiological 6133

Protection recommendations regarding dose calculation,” J. Am. Dent. Assoc. 139(9), 1237–1243. 6134

LUDLOW, J.B., TIMOTHY, R., WALKER, C., HUNTER, R., BENAVIDES, E., SAMUELSON, D.B. 6135

and SCHESKE, M.J. (2014). “Effective dose of dental cone beam CT - a meta-analysis of published 6136

data and additional data for 9 CBCT units,” Dentomaxillofac. Radiol. 44(1), 20140197. 6137

LUKAT, T.D., WONG, J.C. and LAM, E.W. (2013). “Small field of view cone beam CT 6138

temporomandibular joint imaging dosimetry,” Dentomaxillofac. Radiol. 42(10), 20130082. 6139

MACDONALD, J.C., REID, J.A. and BERTHOTY, D. (1983). “Drywall construction as a dental 6140

radiation barrier,” Oral Surg. Oral Med. Oral Pathol. 55(3), 319–326. 6141


274

MAH, P., MCDAVID, W.D. and DOVE, S.B. (2011). “Quality assurance phantom for digital dental 6142

imaging,” Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 112(5), 632–639. 6143

MAHDIAN, M., PAKCHOIAN, A.J., DAGDEVIREN, D., ALZAHRANI, A., JALALI, E., 6144

TADINADA, A. and LURIE, A. (2014). “Using hand-held dental x-ray devices,” J. Am. Dent. 6145

Assoc. 145(11), 1130–1132. 6146

MAILLET, M., BOWLES, W.R., MCCLANAHAN, S.L., JOHN, M.T. and AHMAD, M. (2011). “Cone-6147

beam computed tomography evaluation of maxillary sinusitis,” J. Endod. 37(6), 753–757. 6148

MARQUES, A.P., PERRELLA, A., ARITA, E.S., FENYO-PEREIRA, M. and CAVALCANTI, M.G. 6149

(2010). “Assessment of simulated mandibular condyle lesions by cone beam computed tomography,” 6150

Braz. Oral Res. 24(4), 467–474. 6151

MATHEWS, J.D., FORSYTHE, A.V.,BRADY, Z. BUTLER, M.W., GOERGEN, S.K., BYRNES, G.B., 6152

GILES, G.G., WALLACE, A.B., ANDERSON, P.R., GUIVER, T.A., MCGALE, P., CAIN, T.M., 6153

DOWTY, J.G., BICKERSTAFFE, A.C. and DARBY, S.C. (2013). “Cancer risk in 680 000 people 6154

exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million 6155

Australians,” Br. Med. J. 346, f2360 6156

MILLER, A.B., HOWE, G.R., SHERMAN, G.J., LINDSAY, J.P., YAFFE, M.J., DINNER, P.J., RISCH, 6157

H.A. and PRESTON, D.L. (1989). “Mortality from breast cancer after irradiation during fluoroscopic 6158

examinations in patients being treated for tuberculosis,” N. Engl. J. Med. 321(19), 1285–1289. 6159

MIRACLE, A.C. and MUKHERJI, S.K. (2009a). “Conebeam CT of the head and neck, part 1: Physical 6160

principles,” Am. J. Neuroradiol. 30(6), 1088–1095. 6161

MIRACLE, A.C. and MUKHERJI, S.K. (2009b). “Conebeam CT of the head and neck, part 2: Clinical 6162

applications,” Am. J. Neuroradiol. 30(7), 1285–1292. 6163

MODAN, B., CHETRIT, A., ALFANDARY, E., TAMIR, A., LUSKY, A., WOLF, M. and 6164

SHPILBERG, O. (1998). “Increased risk of salivary gland tumors after low-dose irradiation,” 6165

Laryngoscope 108(7), 1095–1097. 6166

MORANT, J. J., SALVADO, M., HERNANDEZ-GIRON, I., CASANOVAS, R., ORTEGA, R. and 6167

CALZADO, A. (2013). “Dosimetry of a cone beam CT device for oral and maxillofacial radiology 6168

using Monte Carlo techniques and ICRP adult reference computational phantoms,” Dentomaxillofac. 6169

Radiol. 42(3), 92555893. 6170

MOYAL, A.E. (2007). Nationwide Evaluation of X-Ray Trends (NEXT): Tabulation and Graphical 6171

Summary of the 1999 Dental Radiography Survey, CRCPD Publication E-03-6-a, 6172

http://crcpd.org/Pubs/NEXT_docs/NEXT99Dental.pdf (accessed August 4, 2015) (Conference of 6173

Radiation Control Program Directors, Inc., Frankfort, Kentucky). 6174

MUIRHEAD, C.R., O'HAGAN, J.A., HAYLOCK, R.G.E., PHILLIPSON, M.A., WILLCOCK, T., 6175

BERRIDGE, G.L.C. and ZHANG, W. (2009). “Mortality and cancer incidence following 6176


275

occupational radiation exposure: Third analysis of the National Registry for Radiation Workers,” Br. 6177

J. Cancer 100(1), 206–212. 6178

NAKFOOR, C.A. and BROOKS, S.L. (1992). “Compliance of Michigan dentists with radiographic 6179

safety recommendations,” Oral Surg. Oral Med. Oral Pathol. 73(4), 510–513. 6180

NA/NRC (1990). National Academies/National Research Council. Health Effects of Exposure to Low 6181

Levels of Ionizing Radiation: BEIR V (National Academies Press, Washington). 6182

NA/NRC (2006). National Academies/National Research Council. Health Risks from Exposure to Low 6183

Levels of Ionizing Radiation: BEIR VII Phase 2 (National Academies Press, Washington). 6184

NCRP (1966). National Council on Radiation Protection and Measurements. Radiation Protection in 6185

Educational Institutions, NCRP Report No. 32 (National Council on Radiation Protection and 6186


NCRP (1970). National Council on Radiation Protection and Measurements. Dental X-Ray Protection, 6188

NCRP Report No. 35 (National Council on Radiation Protection and Measurements, Bethesda, 6189

Maryland). 6190

NCRP (1976). National Council on Radiation Protection and Measurements. Structural Shielding Design 6191

and Evaluation for Medical Use of X Rays and Gamma Rays of Energies Up to 10 MeV, NCRP 6192

Report No. 49 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). 6193

NCRP (1985). National Council on Radiation Protection and Measurements. SI Units in Radiation 6194

Protection and Measurements, NCRP Report No. 82 (National Council on Radiation Protection and 6195


NCRP (1987a). National Council on Radiation Protection and Measurements. Recommendations on 6197

Limits for Exposure to Ionizing Radiation, NCRP Report No. 91 (National Council on Radiation 6198

Protection and Measurements, Bethesda, Maryland). 6199

NCRP (1987b). National Council on Radiation Protection and Measurements. Ionizing Radiation 6200

Exposure of the Population of the United States, NCRP Report No. 93 (National Council on 6201

Radiation Protection and Measurements, Bethesda, Maryland). 6202

NCRP (1987c). National Council on Radiation Protection and Measurements. Exposure of the Population 6203

in the United States and Canada from Natural Background Radiation, NCRP Report No. 94 (National 6204

Council on Radiation Protection and Measurements, Bethesda, Maryland). 6205

NCRP (1987d). National Council on Radiation Protection and Measurements. Radiation Exposure of the 6206

U.S. Population from Consumer Products and Miscellaneous Sources, NCRP Report No. 95 6207

(National Council on Radiation Protection and Measurements, Bethesda, Maryland). 6208

NCRP (1988). National Council on Radiation Protection and Measurements. Quality Assurance for 6209

Diagnostic Imaging, NCRP Report No. 99 (National Council on Radiation Protection and 6210



276

NCRP (1989a). National Council on Radiation Protection and Measurements. Medical X-Ray, Electron 6212

Beam and Gamma-Ray Protection for Energies Up to 50 MeV (Equipment Design, Performance and 6213

Use), NCRP Report No. 102 (National Council on Radiation Protection and Measurements, Bethesda, 6214

Maryland). 6215

NCRP (1989b). National Council on Radiation Protection and Measurements. Radiation Protection for 6216

Medical and Allied Health Personnel, NCRP Report No. 105 (National Council on Radiation 6217


NCRP (1989c). National Council on Radiation Protection and Measurements. Exposure of the U.S. 6219

Population from Diagnostic Medical Radiation, NCRP Report No. 100 (National Council on 6220


NCRP (1989d). National Council on Radiation Protection and Measurements. Exposure of the U.S. 6222

Population from Occupational Radiation, NCRP Report No. 101 (National Council on Radiation 6223


NCRP (1990). National Council on Radiation Protection and Measurements. The Relative Biological 6225

Effectiveness of Radiations of Different Quality, NCRP Report No. 104 (National Council on 6226


NCRP (1992). National Council on Radiation Protection and Measurements. Maintaining Radiation 6228

Protection Records, NCRP Report No. 114 (National Council on Radiation Protection and 6229


NCRP (1993a). National Council on Radiation Protection and Measurements. Limitation of Exposure to 6231

Ionizing Radiation, NCRP Report No. 116 (National Council on Radiation Protection and 6232


NCRP (1993b). National Council on Radiation Protection and Measurements. Risk Estimates for 6234

Radiation Protection, NCRP Report No. 115 (National Council on Radiation Protection and 6235


NCRP (1997). National Council on Radiation Protection and Measurements. Uncertainties in Fatal 6237

Cancer Risk Estimates Used in Radiation Protection, NCRP Report No. 126 (National Council on 6238


NCRP (1998). National Council on Radiation Protection and Measurements. Operational Radiation 6240

Safety Program, NCRP Report No. 127 (National Council on Radiation Protection and 6241


NCRP (2000). National Council on Radiation Protection and Measurements. Operational Radiation 6243

Safety Training, NCRP Report No. 134 (National Council on Radiation Protection and 6244



277

NCRP (2001). National Council on Radiation Protection and Measurements. Evaluation of the Linear-6246

Nonthreshold Dose-Response Model for Ionizing Radiation, NCRP Report No. 136 (National 6247



Dentistry, NCRP Report No. 145 (National Council on Radiation Protection and Measurements, 6250

Bethesda, Maryland). 6251

NCRP (2004a). National Council on Radiation Protection and Measurements. Structural Shielding 6252

Design for Medical X-Ray Imaging Facilities, NCRP Report No. 147 (National Council on Radiation 6253


NCRP (2004b). National Council on Radiation Protection and Measurements. Recent Applications of the 6255

NCRP Public Dose Limit Recommendation for Ionizing Radiation, NCRP Statement No. 10, 6256

http://ncrponline.org/Publications/Statements/Statement_10.pdf (accessed August 4, 2015) (National 6257


NCRP (2005). National Council on Radiation Protection and Measurements. Structural Shielding Design 6259

and Evaluation for Megavoltage X- and Gamma-Ray Radiotherapy Facilities, NCRP Report No. 151 6260

(National Council on Radiation Protection and Measurements, Bethesda, Maryland). 6261


Educational Institutions, NCRP Report No. 157 (National Council on Radiation Protection and 6263


NCRP (2008). National Council on Radiation Protection and Measurements. Risk to the Thyroid from 6265

Ionizing Radiation, NCRP Report No. 159 (National Council on Radiation Protection and 6266


NCRP (2009). National Council on Radiation Protection and Measurements. Ionizing Radiation Exposure 6268

of the Population of the United States, NCRP Report No. 160 (National Council on Radiation 6269


NCRP (2010a). National Council on Radiation Protection and Measurements. Radiation Dose 6271

Management for Fluoroscopically-Guided Interventional Medical Procedures, NCRP Report No. 6272

168 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). 6273

NCRP (2010b). National Council on Radiation Protection and Measurements. Uncertainties in Internal 6274

Radiation Dose Assessment. NCRP Report No. 164 (National Council on Radiation Protection and 6275


NCRP (2012a). National Council on Radiation Protection and Measurements. Uncertainties in the 6277

Estimation of Radiation Risks and Probability of Disease Causation, NCRP Report No. 171 (National 6278



278

NCRP (2012b). National Council on Radiation Protection and Measurements. Reference Levels and 6280

Achievable Doses in Medical and Dental Imaging: Recommendations for the United States, NCRP 6281

Report No. 172 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). 6282

NCRP (2013). National Council on Radiation Protection and Measurements. Preconception and Prenatal 6283

Radiation Exposure: Health Effects and Protective Guidance, NCRP Report No. 174 (National 6284


NEEL, J.V. and SCHULL, W.J. (1956). The Effect of Exposure to the Atomic Bombs on Pregnancy 6286

Termination in Hiroshima and Nagasaki, Publication No. 461 (National Academies Press, 6287

Washington). 6288

NEUGEBAUER, J., SHIRANI, R., MISCHKOWSKI, R.A., RITTER, L., SCHEER, M., KEEVE, E. and 6289

ZOLLER, J.E. (2008). “Comparison of cone-beam volumetric imaging and combined plain 6290

radiographs for localization of the mandibular canal before removal of impacted lower third molars,” 6291

Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 105(5), 633–642. 6292

NRPB (2001). National Radiological Protection Board. Guidance Notes for Dental Practitioners on the 6293

Safe Use of X-Ray Equipment (Public Health England, London). 6294

O’NEIL, M., KHAMBAY, B., MOOS, K.F., BARBENEL, J., WALKER, F. and AYOUB, A. (2012). 6295

“Validation of a new method for building a three-dimensional physical model of the skull and 6296

dentition,” Br. J. Oral Maxillofac. Surg. 50(1), 49–54. 6297

OSHA (2015). U.S. Occupational Safety and Health Administration. Occupational Safety and Health 6298

Standards, Toxic and Hazardous Substances, Bloodborne Pathogens, 29 CFR Part 1910.1030, 6299

https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=10051 6300

(Accessed February 04, 2016) (U.S. Occupational Safety and Health Administration, Washington). 6301

PAKKALA, T., KUUSELA, L., EKHOLM, M., WENZEL, A., HAITER-NETO, F. and 6302

KORTESNIEMI, M. (2012). “Effect of varying displays and room illuminance on caries diagnostic 6303

accuracy in digital dental radiographs,” Caries Res. 46(6), 568–574. 6304

PALOMO, L. and PALOMO, J.M. (2009). “Cone beam CT for diagnosis and treatment planning in 6305

trauma cases,” Dent. Clin. N. Am. 53(4), 717–727. 6306

PATEL, N., RUSHTON, V.E., MACFARLANE, TV AND HORNER, K (2000). The influence of 6307

viewing conditions on radiological diagnosis of periapical inflammation. British Dental Journal 189, 6308

40-42 6309

PAUWELS, R., BEINSBERGER, J., COLLAERT, B., THEODORAKOU, C., ROGERS, J., WALKER, 6310

A., COCKMARTIN, L., BOSMANS, H., JACOBS, R., BOGAERTS, R. and HORNER, K. (2012). 6311

“Effective dose range for dental cone beam computed tomography scanners,” Eur. J. Radiol. 81(2), 6312

267–271. 6313


279

PEARCE, M.S., SALOTTI, J.A., LITTLE, M.P., MCHUGH, K., LEE, C., KIM, K.P., HOWE, N.L., 6314

RONCKERS, C.M., RAJARAMAN, P., CRAFT, A.W., PARKER, L. and BERRINGTON DE 6315

GONZÁLEZ, A. (2012). “Radiation exposure from CT scans in childhood and subsequent risk of 6316

leukaemia and brain tumours: A retrospective cohort study,” Lancet 380(9840), 499–505. 6317

PLATIN, E., JANHOM, A. and TYNDALL, D. (1998). “A quantitative analysis of dental radiography 6318

quality assurance practices among North Carolina dentists,” Oral Surg. Oral Med. Oral Pathol. Oral 6319

Radiol. Endod. 86(1), 115–120. 6320

PRESTON, D.L., KUSUMI, S., TOMONAGA, M., IZUMI, S., RON, E., KURAMOTO, A., KAMADA, 6321

N., DOHY, H., MATSUO, T., NONAKA, H., THOMPSON, D.E., SODA, M. and MABUCHI, K. 6322

(1994). “Cancer incidence in atomic bomb survivors. Part III. Leukemia, lymphoma and multiple 6323

myeloma, 1950–1987,” Radiat. Res. 137(2 Suppl), S68–S97. 6324

PRESTON, D.L., SHIMIZU, Y., PIERCE, D.A., SUYAMA, A. and MABUCHI, K. (2003). “Studies of 6325

mortality of atomic bomb survivors. Report 13: Solid cancer and noncancer disease mortality: 1950–6326

1997,” Radiat. Res. 160(4), 381–407. 6327

PRESTON, D.L., RON, E., TOKUOKA, S., FUNAMOTO, S., NISHI, N., SODA, M., MABUCHI, K. 6328

and KODAMA, K. (2007). “Solid cancer incidence in atomic bomb survivors: 1958–1998,” Radiat. 6329

Res. 168(1), 1–64. 6330

PRICE, C. (1995). “Sensitometric evaluation of a new E-speed dental radiographic film,” 6331

Dentomaxillofac. Radiol. 24(1), 30–36. 6332

PRINS, R., DAUER, L.T., COLOSI, D.C., QUINN, B., KLEIMAN, N.J., BOHLE, G.C., HOLOHAN, 6333

B., AL-NAIJAR, A., FERNANDEZ, T., BONVENTO, M., FABER, R.D., CHING, H., GOREN, 6334

A.D. (2011). “Significant reduction in dental cone beam computed tomography (CBCT) eye dose 6335

through the use of leaded glasses,” Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 112(4), 502–6336

5077. 6337

PUSKIN, J.S. (2009). “Perspective on the use of LNT for radiation protection and risk assessment by the 6338

U.S. Environmental Protection Agency,” Dose Response 7(4), 284–291. 6339

QU, X.M., LI, G., LUDLOW, J.B., ZHANG, Z.Y. and MA, X.C. (2010). “Effective radiation dose of 6340

ProMax 3D cone-beam computerized tomography scanner with different dental protocols,” Oral 6341

Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 110(6), 770–776. 6342

QU, X., LI, G., ZHANG, Z. and MA, X. (2012a). “Thyroid shields for radiation dose reduction during 6343

cone beam computed tomography scanning for different oral and maxillofacial regions,” Eur. J. 6344

Radiol. 81(3), e376–e380. 6345

QU, X.M., LI, G., SANDERINK, G.C.H., ZHANG, Z.Y. and MA, X.C. (2012b). “Dose reduction of 6346

cone beam CT scanning for the entire oral and maxillofacial regions with thyroid collars,” 6347



280

RATHORE, S., TYNDALL, D., WRIGHT, J.T. and EVERETT, E. (2012). “Ex vivo comparison of 6349

Galileos cone beam CT and intraoral radiographs in detecting occlusal caries,” Dentomaxillofac. 6350

Radiol. 41(6), 489–493. 6351

RICHARDS, A.G. (1964). “Sources of x-radiation in the dental office,” Dent. Radiogr. Photogr. 37(3), 6352

51–68. 6353

RICHARDS, A.G. and COLQUITT, W.N. (1981). “Reduction in dental x-ray exposures during the past 6354

60 years,” J. Am. Dent. Assoc. 103(5), 713–718. 6355

REID, J.A. and MACDONALD, J.C. (1984). “Use and workload factors in dental radiation-protection 6356

design,” Oral Surg. Oral Med. Oral Pathol. 57(2), 219–224. 6357

REID, J.A., MACDONALD, J.C.F., DEKKER, T.A. and KUPPERS, B.U. (1993). “Radiation exposures 6358

around a panoramic dental x-ray unit,” Oral Surg. Oral Med. Oral Pathol. 75(6), 780–782. 6359

RITTER, L., LUTZ, J., NEUGEBAUER, J., SCHEER, M., DREISEIDLER, T., ZINSER, M.J., 6360

ROTHAMEL, D. and MISCHKOWSKI, R.A. (2011). “Prevalence of pathologic findings in the 6361

maxillary sinus in cone-beam computerized tomography,” Oral Surg. Oral Med. Oral Pathol. Oral 6362

Radiol. Endod. 111(5), 634–640. 6363

ROBERTS, J.A., DRAGE, N.A., DAVIES, J. and THOMAS, D.W. (2009). “Effective dose from cone 6364

beam CT examinations in dentistry,” Br. J. Radiol. 82(973), 35–40. 6365

RON, E., MODAN, B., BOICE, J.D., JR., ALFANDARY, E., STOVALL, M., CHETRIT, A. and KATZ, 6366

L. (1988). “Tumors of the brain and nervous system after radiotherapy in childhood,” N. Engl. J. 6367

Med. 319(16), 1033–1039. 6368

RON, E., MODAN, B., PRESTON, D., ALFANDARY, E., STOVALL, M. and BOICE, J.D., JR. (1989). 6369

“Thyroid neoplasia following low-dose radiation in childhood,” Radiat. Res. 120(3), 516–531. 6370

ROSENBERG, P.A., FRISBIE, J., LEE, J., LEE, K., FROMMER, H., KOTTAL, S., PHELAN, J., LIN, 6371

L. and FISCH, G. (2010). “Evaluation of pathogenesis (histopathology) and radiologists (cone beam 6372

computed tomography) differentiating radicular cysts from granulomas,” J. Endod. 36(3), 423–428. 6373

ROTTKE, D., PATZELT, S., POXLEITNER, P. and SCHULZE, D. (2013). “Effective dose span of ten 6374

different cone beam CT devices,” Dentomaxillofac. Radiol. 42(7), 20120417. 6375

RUBIN, P. and CASARETT, G.W. (1968). Clinical Radiation Pathology (WB Saunders, Philadelphia). 6376

RUMBERG, H., HOLLENDER, L. and ODA, D. (1996). “Assessing the quality of radiographs 6377

accompanying biopsy specimens,” J. Am. Dent. Assoc. 127(3), 363–368. 6378

SCHILLING, R. and GEIBEL, M.A. (2013). “Assessment of the effective doses from two dental cone 6379

beam CT devices,” Dentomaxillofac. Radiol. 42(5), 20120273. 6380

SHAHBAZIAN, M., VANDERWOUDE, C., WYATT, J. and JACOBS, R. (2014). “Comparative 6381

assessment of panoramic radiography and CBCT imaging for radiodiagnostics in the posterior 6382

maxilla,” Clin. Oral Investig. 18(1), 293–300. 6383


281

SHANBHAG, S., KARNIK, P., SHIRKE, P. and SHANBHAG, V. (2013). “Association between 6384

periapical lesions and maxillary sinus mucosal thickening: A retrospective cone-beam computed 6385

tomographic study,” J. Endod. 39(7), 853–857. 6386

SHINTAKU, W.H., VENTURIN, J.S., AZEVEDO, B. and NOUJEIM, M. (2009). “Applications of 6387

cone-beam computed tomography in fractures of the maxillofacial complex,” Dent. Traumatol. 25(4), 6388

358–366. 6389

SHORE, R.E., WOODARD, E., HILDRETH, N., DVORETSKY, P., HEMPELMANN, L. and 6390

PASTERNACK, B. (1985). “Thyroid tumors following thymus irradiation,” J. Natl. Cancer Inst. 6391

74(6), 1177–1184. 6392

SHORE, R.E., HILDRETH, N., DVORETSKY. P., ANDRESEN, E., MOSESON, M. and 6393

PASTERNACK, B. (1993). “Thyroid cancer among persons given x-ray treatment in infancy for an 6394

enlarged thymus gland,” Am. J. Epidemiol. 137(10), 1068–1080. 6395

SIMON, J.H.S., ENCISO, R., MALFAZ, J.M., ROGES, R., BAILEY-PERRY, M. and PATEL, A. 6396

(2006). “Differential diagnosis of large periapical lesions using cone-beam computed tomography 6397

measurements and biopsy,” J. Endod. 32(9), 833–837. 6398

SIMPKIN, D.J. and DIXON, R.L. (1998). “Secondary shielding barriers for diagnostic x-ray facilities: 6399

Scatter and leakage revisited,” Health Phys. 74(3), 350–365. 6400

SPR (2015). Society for Pediatric Radiology. Image Gently, http://www.imagegently.org (accessed 6401

August 4, 2015) (Society for Pediatric Radiology, Reston, Virginia). 6402

STRATEMANN, S.A., HUANG, J.C., MAKI, K., MILLER, A.J. and HATCHER, D.C. (2008). 6403

“Comparison of cone beam computed tomography imaging with physical measures,” 37(2), 80–93. 6404

SULEIMAN, O.H., CONWAY, B.J., FEWELL, T.R., SLAYTON, R.J., RUETER, F.G. and GRAY, J. 6405

(1995). “Radiation protection requirements for medical x-ray film,” Med. Phys. 22(10), 1691–1693. 6406

SUOMALAINEN, A., KILJUNEN, T., KASER, Y., PELTOLA, J. and KORTESNIEMI, M. (2009). 6407

“Dosimetry and image quality of four dental cone beam computed tomography scanners compared 6408

with multislice computed tomography scanners,” Dentomaxillofac. Radiol. 38(6), 367–378. 6409

SUOMALAINEN, A., VENTA, I., MATTILA, M., TURTOLA, L., VEHMAS, T. and PELTOLA, J.S. 6410

(2010). “Reliability of CBCT and other radiographic methods in preoperative evaluation of lower 6411

third molars,” Oral Surg. Oral Med. Oral Pathol. Oral Radiol. Endod. 109(2), 276–284. 6412

SVENSON, B. and PETERSSON, A. (1995). “Questionnaire survey on the use of dental x-ray film and 6413

equipment among general practitioners in the Swedish Public Dental Health Service,” Acta Odontol. 6414

Scand. 53(4), 230–235. 6415

SVENSON, B., SODERFELDT, B. and GRONDAHL, H.G. (1996). “Attitudes of Swedish dentists to the 6416

choice of dental x-ray film and collimator for oral radiology,” Dentomaxillofac. Radiol. 25(3), 157–6417

161. 6418


282

SVENSON, B.., WELANDER, U., SHI, X.Q., STAMATAKIS, H. and TRONJE, G. (1997a). “A 6419

sensitometric comparison of four dental x-ray films and their diagnostic accuracy,” Dentomaxillofac. 6420

Radiol. 26(4), 230–235. 6421

SVENSON, B., SODERFELDT, B. and GRONDAHL, H. (1997b). “Knowledge of radiology among 6422

Swedish dentists,” Dentomaxillofac. Radiol. 26(4), 219–224. 6423

SVENSON, B., GRONDAHL, H.G., and SODERFELDT, B. (1998). “A logistic regression model for 6424

analyzing the relation between dentists’ attitudes, behavior, and knowledge in oral radiology,” Acta. 6425

Odontol. Scand. 56(4), 215–219. 6426

SYRIOPOULOS, K., VELDERS, X.L., SANDERINK, G.C.H. and VAN DER STELT, P.F. (2001). 6427

“Sensitometric and clinical evaluation of a new F-speed dental x-ray film,” Dentomaxillofac. Radiol. 6428

30(1), 40–44.TADINADA, A., MAHDIAN, M., SHETH, S., CHANDHOKE, T.K., POTLURI, A. 6429

and YADAV, S. (2015a). “Reliability of tablet computers in depicting radiographic landmarks in the 6430

maxillofacial region,” Imaging Sci. Dent. 45(3), 175–180. 6431

TADINADA, A., FUNG, K., THACKER, S., MAHDIAN, M., JADHAV, A. and SCHINCAGLIA, G.P. 6432

(2015b). “Radiographic evaluation of the maxillary sinus prior to dental implant therapy: A 6433

comparison between two-dimensional and three-dimensional radiographic imaging,” Imaging Sci. 6434

Dent. 45(3),169–174. 6435

TAMBURUS, J.R. and LAVRADOR, M.A. (1997). “Radiographic contrast. A comparative study of 6436

three dental x-ray films,” Dentomaxillofac. Radiol. 26(4), 201–205. 6437

TANIMOTO, K., OGAWA, M., KODERA, Y., TOMITA, S. and WADA, T. (1989). “A filter for use in 6438

lateral cephalography,” Oral Surg. Oral Med. Oral Pathol. 68(5), 666–669. 6439

THEODORAKOU, C., WALKER, A., HORNER, K., PAUWELS, R., BOGAERTS, R. and JACOBS, R. 6440

(2012). “Estimation of paediatric organ and effective doses from dental cone beam CT using 6441

anthropomorphic phantoms,” Br. J. Radiol. 85(1010), 153–160. 6442

THUNTHY, K.H. (2000) “Clinical trial of new F-speed film from Kodak finds contrast, resolution, equal 6443

to D-speed,” Contemp. Esthetics Restorat. Pract. 4(8), 38–39. 6444

THUNTHY, K.H. and WEINBERG, R. (1982). “Sensitometric comparison of dental films of groups D 6445

and E,” Oral Surg. Oral Med. Oral Pathol. 54(2), 250–252. 6446

THUNTHY, K.H. and WEINBERG, R. (1986). “Sensitometic and image analysis of T-grain film,” Oral 6447

Surg. Oral Med. Oral Pathol. 62(2), 218–220. 6448

TJELMELAND, E.M., MOORE, W.S., HERMESCH, C.B. and BUIKEMA, D.J. (1998). “A 6449

perceptibility curve comparison of Ultra-speed and Ektaspeed Plus films,” Oral Surg. Oral Med. Oral 6450

Pathol. Oral Radiol. Endod. 85(4), 485–488. 6451

TYNDALL, D.A. and RATHGORE, S. (2008). “Cone-beam CT diagnostic applications: Caries, 6452

periodontal bone assessment, and endodontic applications,” Dent. Clin. N. Am. 52(4), 825–841. 6453


283

TYNDALL, D.A., PRICE, J.B., TETRADIS, S., GANZ, S.D., HILDEBOLT, C. and SCARFE, W.C. 6454

(2012). “Position statement of the American Academy of Oral and Maxillofacial Radiology on 6455

selection criteria for the use of radiology in dental implantology with emphasis on cone beam 6456

computed tomography,” Oral Surg. Oral Med. Oral Pathol. Oral Radiol. 113(6), 817–826. 6457

UDUPA, H., MAH, P., DOVE, S.B. and MCDAVID, W.D. (2013). “Evaluation of image quality 6458

parameters of representative intraoral digital radiographic systems,” Oral Surg. Oral Med. Oral 6459

Pathol. Oral Radiol. Endod 116(6), 774–783. 6460

UNDERHILL, T.E., CHILVARQUER, I., KIMURA, K., LANGLAIS, R.P., MCDAVID, W.D., 6461

PREECE, J.W. and BARNWELL, G. (1988). “Radiobiologic risk estimation from dental radiology: 6462

Part I. Absorbed doses to critical organs,” Oral Surg. Oral Med. Oral Pathol. 66(1), 111–120. 6463

UNSCEAR (2000). United Nations Scientific Committee on the Effects of Atomic Radiation. Sources 6464

and Effects of Ionizing Radiation, UNSCEAR 2000 Report to the General Assembly, with Scientific 6465

Annexes. Volume I: Sources, Publication E.00.IX.3 (United Nations, New York). 6466

UNSCEAR (2010). United Nations Scientific Committee on the Effects of Atomic Radiation. Sources 6467


Annexes (United Nations, New York). 6469

UNSCEAR (2012). United Nations Scientific Committee on the Effects of Atomic Radiation. Sources, 6470

Effects and Risks of Ionizing Radiation, UNSCEAR 2012 Report to the General Assembly, Scientific 6471

Annex A, Uncertainties in risk estimates for radiation-induced cancer (United Nations, New York). 6472

UNSCEAR (2013). United Nations Scientific Committee on the Effects of Atomic Radiation. Sources, 6473

Effects and Risks of Ionizing Radiation, UNSCEAR 2013 Report to the General Assembly with 6474

Scientific Annexes. Volume II, Scientific Annex B, Effects of radiation exposure of children (United 6475

Nations, New York). 6476

UNSCEAR (2015a). United Nations Scientific Committee on the Effects of Atomic Radiation. Sources 6477


Annexes. Scientific Annex B, Uncertainties in risk estimates for radiation-induced cancer (United 6479

Nations, New York). 6480

UNSCEAR (2015b). United Nations Scientific Committee on the Effects of Atomic Radiation. Sources 6481


Annexes. Scientific Annex A, Attributing health effects to ionizing radiation exposure and inferring 6483

risks (United Nations, New York). 6484

VALACHOVIC, R.W., REISKIN, A.B. and KIRCHHOF, S.T. (1981). “A quality assurance program in 6485

dental radiology,” Pediatr. Dent. 3(1), 26–32. 6486

VAN AKEN, J. and VAN DER LINDEN, L.W.J. (1966). “The integral absorbed dose in conventional 6487

and panoramic complete-mouth examinations,” Oral Surg. Oral Med. Oral Pathol. 22(5), 603–616. 6488


284

VANDENBERGHE, B., JACOBS, R. and YANG, J. (2008). “Detection of periodontal bone loss using 6489

digital intraoral and cone beam computed tomography images: An in vitro assessment of bony and/or 6490

infrabony defects,” Dentomaxillof. Radiol. 37(5), 252–260. 6491

WALKER, T.F., MAH, P., DOVE, S.B., and MCDAVID, W.D. (2014) “Digital intraoral radiographic 6492

quality assurance and control in private practice,” Gen. Dent. 62(5), 22–29. 6493

WALTER, C., WEIGER, R. and ZITZMANN, N.U. (2010). “Accuracy of three-dimensional imaging in 6494

assessing maxillary molar furcation involvement,” J. Clin. Periodontol. 37(5), 436–441. 6495

WANG, P., YAN, X.B., LUI, D.G., ZHANG, W.L., ZHANG, Y. and MA, X.C. (2011). “Detection of 6496

dental root fractures by using cone-beam computed tomography,” Dentomaxillofac. Radiol. 40(5), 6497

290–298. 6498

WENZEL, A., HIRSCH, E., CHRISTENSEN, J., MATZEN, L.H., SCAL, G. and FRYDENBERG, M. 6499

(2014). “Detection of cavitated approximal surfaces using cone beam CT and intraoral receptors,” 6500

Dentomaxillofac. Radiol. 42(1), 39458105. 6501

WHITE, S.C. (1992). “1992 assessment of radiation risk from dental radiography,” 6502


WHITE, S.C. (2008). “Cone-beam imaging in dentistry,” Health Phys. 95(5), 628–637. 6504

WHITE S.C. and PAE, E.K. (2009). “Patient image selection criteria for cone beam computed 6505

tomography imaging,” Semin. Orthod. 15(1), 19–28. 6506

WHITE, S.C. and PHARAOH, M.J. (2014). Oral Radiology. Principles and Interpretation, 7th ed. 6507

(Elsevier-Mosby, St. Louis, Missouri). 6508

WILSON (1979). “Analyzing the risks of daily live,” Technol. Rev. 81(6), 41-46. 6509

XU, J., REH, D.D., CAREY, J.P., MAHESH, M. and SIEWERDSEN, J.H. (2012). “Technical 6510

assessment of a cone-beam CT scanner for otolaryngology imaging: Image quality, dose, and 6511

technique protocols,” Med. Phys. 39(8), 4932–4942. 6512

YADAV, S., PALO, L., MAHDIAN, M., UPADHYAY, M. and TADINADA, A. (2015). “Diagnostic 6513

accuracy of 2 cone-beam computed tomography protocols for detecting arthritic changes in 6514

temporomandibular joints,” Am. J. Orthod. Dentofacial. Orthop. 147(3), 339–344. 6515

ZIELINSKI, J.M., GARNER, M.J., KREWSKI, D., ASHMORE, J.P., BAND, P.R., FAIR, M.E., JIANG, 6516

H., LETOURNEAU, E.G., SEMENCIW, R. and SONT, W.N. (2005). “Decreases in occupational 6517

exposure to ionizing radiation among Canadian dental workers,” J. Can. Dent. Assoc. 71(1), 29–33. 6518

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