Radiation Protection

Essentials of Dental Radiographyfor Dental Assistants and Hygienists

CHAPTER

Copyright ©2012 by Pearson Education, Inc.All rights reserved.

Essentials of Dental Radiography for Dental Assistants and Hygienists, Ninth EditionEvelyn M. Thomson • Orlen N. Johnson

NINTH EDITIONNINTH EDITION

Radiation Protection

6



Objectives

• Define the key words.• Adopt the ALARA concept.• Use the selection criteria guidelines to

explain the need for prescribed radiographs.

• Explain the roles communication, working knowledge of quality radiographs, and education play in preventing unnecessary radiation exposure.



Objectives

• Explain the roles technique and exposure choices play in preventing unnecessary radiation exposure.

• Explain the function of the filter.• State the filtration requirements for an

intraoral dental x-ray unit that operates above and below 70 kVp.



Objectives

• Compare inherent, added, and total filtration.

• State the federally mandated diameter of the intraoral dental x-ray beam at the patient’s skin.

• Explain the difference between round and rectangular collimation.

• List the two functions of a collimator.



Objectives

• Explain how PID shape and length contribute to reducing patient radiation exposure.

• Identify film speeds currently available for dental radiography use.

• Explain the role image receptor holders play in reducing patient radiation exposure.



Objectives

• Advocate the use of the lead/lead equivalent thyroid collar and apron.

• Explain the role darkroom protocol and film handling play in reducing patient radiation exposure.

• Summarize the radiation protection methods for the patient.



Objectives

• Explain the roles time, shielding, and distance play in protecting the radiographer from unnecessary radiation exposure.

• Utilize distance and location to take a position the appropriate distance and angle from the x-ray source at the patient’s head during an exposure.



Objectives

• Describe monitoring devices used to detect radiation.

• Summarize the radiation protection methods for the radiographer.



Objectives

• List the organizations responsible for recommending and setting exposure limits.

• State the maximum permissible dose (MPD) for radiation workers and for the general public.



Key Words

• Added filtration• ALARA (as low as reasonably achievable)• Aluminum equivalent• Area monitoring• Collimation



Key Words

• DIS (direct ion storage) monitor• Dosimeter• Exposure factors• Film badge• Film/image receptor holder• Filter



Key Words

• Filtration• Half-value layer• Inherent filtration• Lead apron• Lead equivalent• MPD (maximum permissible dose) • Monitoring



Key Words

• OSL (optically stimulated luminescence) monitor

• Personnel monitoring• Personnel monitoring device



Key Words

• PID (position indicating device)/BID (beam indicating device)

• Primary beam• Protective barrier• Radiation leakage• Radiation workers



Key Words

• Retake radiographs• Scatter (secondary) radiation• Selection criteria• Structural shielding• Thermoluminescent dosimeter (TLD)• Thyroid collar• Total filtratio



Introduction

• Although it is the consensus of radiobiologists that the dose received from a dental x-ray exposure is not likely to be harmful, even the experts do not know what risk a small dose carries.



Introduction

• The patient has agreed to be subjected to the risks of radiation exposure because he/she believes that the oral health care practitioner will follow safety protocols that protect the patient from excess exposure.



Introduction

• In this chapter, we discuss radiation safety protocols, including selection criteria used in prescribing dental radiographs and methods to minimize x-ray exposure to both the dental patient and the radiographer.



ALARA

“As Low As Reasonably Achievable”



Protection Measures for the Patient

• Professional judgment• Technical ability of the operator• Technique standards• Equipment standards• Optimum film processing



Protection Measuresfor the Patient

• Professional Judgment – Use evidence-based selection criteria when

determining which patients need radiographs. – Guidelines adopted by the American Dental

Association that assist in deciding when, what type, and how many radiographs should be taken are shown in Table 6-1.



Table 6-1 Guidelines for Prescribing Dental Radiographs










• Technical Ability of the Operator– Communication — clear instructions; patient

cooperation– Working knowledge of quality radiographs —

understand what a quality dental radiograph should image

– Education — continuing education is important




• Technique Standards– Intraoral technique choice — first choice; The

paralleling technique yields more accurate and precisely sized radiographic images

– Exposure factors — select the appropriate exposure factors — kilovoltage (kVp), milliamperage (mA), and time.




• Equipment Standards: The Federal Performance Standard for Diagnostic X-ray Equipment, effective August 1974.– Provisions require that all x-ray equipment

manufactured after this date meet certain radiation safety requirements including filtration, collimation, and PID



Figure 6-1 Collimator and filter. The collimator is a lead washer that restricts the size of the x-ray beam. The filter is an aluminum disc that filters (removes) the long wavelength x-rays.



Figure 6-2 Effect of filtration on skin exposure. Aluminum filters selectively absorb the long wavelength x-rays.



Figure 6-3 Effect of collimation on primary beam. Lead collimators control the shape and size of the primary beam. The beam is limited to the approximate size of the image receptor.



Figure 6-4 External collimator attaches to the PID to reduce the area of radiation exposure.



Figure 6-5 The collimator restricts the size of the primary beam to 2.75 in. (7 cm) at the end of the PID.



Figure 6-6 Although circular collimation provides a large enough area of exposure to adequately cover a size #2 image receptor, the patient also receives excess radiation not needed for the exposure of this receptor.



Figure 6-7 Rectangular PIDs restrict the x-ray beam to the approximate size of a #2 intraoral image receptor. Rectangular PIDs are available in 8, 12, and 16 inches (20.5, 30, and 41 cm). (Courtesy of Margraf Dental Manufacturing Inc.)



Figure 6-8 Plastic closed-ended, pointed “cones” are no longer used.



Figure 6-9 Round PIDs are available in 16, 12, and 8 inches (41, 30, and 20.5 cm).



Figure 6-10 Target-surface distance. The longer the target-surface distance, the more parallel the x-rays and the less tissue exposed. Note that the beam size at the patient’s skin entrance is 2.75 in. (7 cm) for both target-surface distances. It is the exit beam size that increases to expose a larger area when using the shorter target-surface distance.



Figure 6-11 Many image receptor holding devices are available to fit most situations. The use of a holder prevents asking patients to put their fingers in the path of the primary beam.



Figure 6-12 Lead aprons and thyroid collars are available in a wide range of sizes. Aprons are available with an attached thyroid collar, or the thyroid collar may be a separate part.



Figure 6-13 Patient protected with lead apron with thyroid collar in place.




• Optimum Film Processing– Processing errors increase patient radiation

exposure by resulting in retake radiographs.– Patient protection techniques should be used

at all times to keep radiation exposures as low as possible



Box 6-1 Summary of Protection Methods for the Patient



Protection Methods for the Radiographer

• All measures taken to protect the patient from radiation also benefit the radiographer.

• Radiation protection methods include time, shielding, and distance.

• The radiographer should spend a minimal amount of time, protected by shielding, at the greatest distance from the source of radiation to avoid unnecessary exposure.



Box 6-2 Summary of Methods to Protect the Radiographer



Figure 6-14 Distance is an effective means of reducing exposure from scatter radiation.



Figure 6-15 When structural shielding is not available, the radiographer should stand in a position at least 6 ft (1.83 m) from the head of the patient at an angle of 45º to the exiting primary beam.



Radiation Monitoring

• Area monitoring• Personnel monitoring: Types

– Film badge – Thermoluminescent dosimeter (TLD)– OSL (optimally stimulated luminescence)

monitor – DIS (direct ion stimulation) monitor



Table 6-2 Types of Personnel Monitoring Devices



Figure 6-16 OSL radiation monitor worn by the radiographer to monitor radiation exposure. (Courtesy of Landauer, Inc.)



Figure 6-17 DIS radiation monitor. Sized and shaped similar to a thumb drive, this device has a clip to allow the radiographer to wear the monitor while working with ionizing radiation. The device uses a USB connector to plug into a computer with Internet access. When logged on to the manufacturer’s Web site, real-time radiation exposure readings may be downloaded from the device. (Courtesy of Quantum Products.)



Organizations Responsible for Recommending/Setting Exposure Limits

• Maximum permissible dose (MPD)– Radiation workers– General public



Table 6-3 Radiation Protection Organizations



Guides for Maintaining Safe Radiation Levels

• Radiation safety legislation



Review: Chapter Summary

• Oral healthcare professionals have an ethical responsibility to adopt the ALARA concept.

• The most important step in keeping the patient’s exposure to a minimum is the use of evidenced-based selection criteria to assess patients for radiographic need.




• The technical ability of the radiographer will aid in preventing unnecessary radiation exposure to the patient. Technical ability includes: communication, working knowledge of quality radiographs, and education.




• Technique standards, including the choice of paralleling or bisecting technique, and the selection of exposure factors also aid in preventing unnecessary radiation exposure.




• Equipment standards that play an important role in reducing patient radiation dose include collimation, filtration, and PID length.

• Filtration is the absorption of long wavelength, less penetrating x-rays from the x-ray beam by passage through a sheet of material called a filter.




• Present safety standards require an equivalent of 1.5 mm aluminum filtration for dental x-ray machines operating in ranges below 70 kVp and a minimum of 2.5 mm aluminum for machines operating at or above 70 kVp. Total filtration is the sum of inherent and added filtration.




• Collimation — control of the size and shape of the useful beam. Federal regulations require round opening collimators restrict the x-ray beam to 2.75 in. (7 cm) at the patient end of the PID. Rectangular collimation reduces patient radiation dose by 70 percent over round collimation. Collimation reduces scattered radiation that contributes to poor contrast of radiographic images.




• (PID) is an extension of the tube housing; used to direct the primary x-ray beam. The length of the PID helps establish the desired target–surface distance. PIDs have either a round or rectangular shape and are available in lengths of 8 in. (20.5 cm), 12 in. (30 cm), and 16 in. (41 cm)




• Fast film requires less radiation for exposure. Film speed groups D, E, or F are currently available for use in dental radiography.

• The use of digital image receptors can further reduce the radiation dose to the patient.




• Image receptor holders eliminate using the patient’s fingers to stabilize the receptor intraorally, avoiding unnecessary radiation exposure to the patient’s fingers.

• A lead or lead-equivalent thyroid collar with apron should be placed on all patients during intraoral x-ray exposures.




• Optimum film processing using time — temperature techniques in an adequately equipped darkroom will help avoid retakes.

• Reduce operator exposure — reduce time spent near the source of radiation; use structural shielding; or stand 6 feet away from the source of radiation at a 45-degree angle to the exiting primary beam.




• Area and personnel radiation monitoring can be used to measure radiation exposures. The ICRP and the NCRP recommend dose limits. Federal, state, and local agencies set regulations governing exposure.




• The American Dental Association and the American Academy of Oral and Maxillofacial Radiology work closely with all agencies responsible for radiation safety.




• The maximum permissible dose (MPD) is 50 mSv (5 rem) per year for radiation workers and 5 mSv (0.5 rem) for the general public, radiation workers who are pregnant, and children under 18 years of age.



Recall: Study Questions

• General• Chapter Review



Reflect: Case Study

• Use the selection criteria guidelines to make a preliminary recommendation and/or to explain to the patient why the dentist has prescribed or has not prescribed radiographs. Consider the following three cases:



Reflect: Case Study

1. A 17-year-old patient presents with a healthy oral assessment. No active caries were clinically detected. No periodontal pockets were noted. His record indicates that his last radiographs were bitewings taken 6 months ago. Based on the evidence-based selection criteria guidelines, what would be the most likely recommendation for radiographs for this patient?



Reflect: Case Study

2. A 25-year-old female recall patient presents for her 6-month check-up. Although her homecare is good, Class II (multisurface) restorations are present on several molars and premolars. Her last radiographs were bitewings taken 3 years ago. Based on the evidence-based selection criteria guidelines, what would be the most likely recommendation for radiographs for this patient?



Reflect: Case Study

3. A 45-year-old male patient, new to your practice, presents with a moderate periodontal condition and evidence of generalized dental disease. He reveals that he has not been “to the dentist” in several years, but is here today to begin to “take care of his teeth.” Based on the evidence-based selection criteria guidelines, what would be the most likely recommendation for radiographs for this patient?



Relate: Laboratory Application

• Proceed to Chapter 6, Laboratory Application, to complete this activity.

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