Radiation Dosimetry

John Gough, MS, CHP

Radiation Safety Officer

Swedish Medical Center

Introduction

Swedish Medical Center

• Established in 1910• 3 Hospital locations• Multiple specialty clinics • Cancer, Heart, Surgery institutes• 12 primary-care clinics• Full range nuclear med, radiation oncology • Research Hospital• Type A Medical Broad Scope License

History

History

• X-rays discovered in 1895

• Radioactivity discovered in 1896

• First document radiation fatality – 1904– Clarence Daly severely burned in

1986 by an x-ray fluoroscope

History

• First attempt at establishing a radiation dose limit – Skin Erythema Dose – 1920

• 200 mR/day dose limit established in 1931

• 25,000 mrem/year established during WWII.

Radiation Dosimeters

Radiation Dosimetry

• scientific determination of amount, rate, and distribution of radiation emitted from a source of ionizing radiation, in biological d. measuring the radiation-induced changes in a body or organism, and in physical d. measuring the levels of radiation directly with instruments.

Types of Dosimeters

• Immediate Read– Pocket Ionization Chambers, Solid state

detectors, handheld GM/Ionization detectors with dose accumulation function

• Delayed read / Personnel monitors– Film Badges, TLD (Thermo Luminescent

Dosimeters), OSL (Optically Stimulated Light-emitting Dosimeters)

Film Badges

• Most common type of radiation dosimeter used.

• Works by darkening of x-ray film in proportion to radiation absorbed.

• Cheap• Not durable• Short monitoring period per

badge (6 months or less)

TLD

• “Captures” radiation dose information in a crystal matrix

• Releases light when heated, light intensity proportional to radiation dose absorbed

• Durable• Can be expensive (reusable

chips)• Information destroyed when

processed

OSL

• “Captures” information in an Aluminum Oxide matrix

• Releases information by laser stimulation

• Can be reread after processing• Durable• Landauer Only

Pocket Ionization

• Electro-statically charged “leaf” discharges as it is exposed to ionizing radiation

• Not considered a “legal” record• Low accuracy (+/- 20%)• Physical impacts can affect

radiation dose readings

Solid State

• Provides instantaneous information regarding dose accumulation

• Simple to use

• Not a “legal” record

• Dose range device dependent

Handheld Radiation Detectors

• Ability to perform both dose rate and dose accumulation

• Good for spot checks

• Direction dependent

• Not considered a “legal” personnel dose record

Dose Limits

Occupational Dose

"Occupational dose" means the dose received by an individual in the course of employment in which the individual's assigned duties involve exposure to radiation or to radioactive material from licensed and unlicensed sources of radiation, whether in the possession of the licensee, registrant, or other person. Occupational dose does not include dose received: From background radiation, from any medical administration the individual has received, from exposure to individuals administered radioactive material and released under chapter 246-240 WAC, from voluntary participation in medical research programs, or as a member of the public.

Radiation Doses Comparison

Activity Dose (mrem)1 day of background radiation 1 mrem

1 Chest x-ray 10 mrem

Public Dose Limit 100 mrem

Nuclear Stress Test 500+ mrem

Whole Body CT 1000+ mrem

Occupational Dose LimitsNRC / WA DOH

Part of Body Annual Limit (mrem)

Whole Body (TEDE) 5,000

Organ or Extremity 50,000

Lens of the Eye 15,000

Dose to Fetus 500

Occupational Dose LimitsNRCP Recommendations

* Not to exceed 1000 mrem x Individual’s Age for Cumulative Lifetime exposure.

Part of Body Annual Limit (mrem)

Whole Body (TEDE)* 5,000*

Organ or Extremity 50,000

Lens of the Eyes 15,000

ALARA Concept

“As Low As Reasonably Achievable” means making every reasonable effort to minimize the dose received when working with sources of radiation. Essentially it means minimizing the risks while understanding that the cost vs. benefit for the dose reduction.

Typical ALARA Levels

Part of Body Quarterly Action Level

(mrem)

Level I Level II

Whole Body 125 375

Organ or Extremity 1250 3750

Lens of the Eyes 375 1125

Fetal n/a 150

Dosimetry Reports

Expected Doses from Radiography Sources

Radiography Sources

Isotope Typical Activity (Ci)

Gamma Constant (R/hr – Ci @1 meter)

Dose rate

(R/hr @ 1m)

Ir-192 100 0.48 48

Co-60 20 1.32 26.4

Se-75 100 0.2 20

X-ray n/a