Radiation Dosimetry

1. Radiation Dosimetry John Gough, MS, CHP Radiation Safety Officer Swedish Medical Center

2. Introduction

3. 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

4. History

5. 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

6. 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.

7. Radiation Dosimeters

8. 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.

9. 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)

10. 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)

11. 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

12. OSL • “Captures” information in an Aluminum Oxide matrix • Releases information by laser stimulation • Can be reread after processing • Durable • Landauer Only

13. 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

14. Solid State • Provides instantaneous information regarding dose accumulation • Simple to use • Not a “legal” record • Dose range device dependent

15. 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

16. Dose Limits

17. 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.

18. Radiation Doses Comparison

19. Occupational Dose LimitsNRC / WA DOH

20. Occupational Dose LimitsNRCP Recommendations * Not to exceed 1000 mrem x Individual’s Age for Cumulative Lifetime exposure.

21. 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.

22. Typical ALARA Levels

23. Dosimetry Reports

32. Expected Doses from Radiography Sources

33. Radiography Sources