Radiographers - Radiation dosimetry

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  • Radiographers - Radiation dosimetry

    1. 1. Radiation Dosimetry John Gough, MS, CHP Radiation Safety Officer Swedish Medical Center
    2. 2. Introduction
    3. 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. 4. History
    5. 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. 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. 7. Radiation Dosimeters
    8. 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. 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. 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. 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. 12. OSL • “Captures” information in an Aluminum Oxide matrix • Releases information by laser stimulation • Can be reread after processing • Durable • Landauer Only
    13. 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. 14. Solid State • Provides instantaneous information regarding dose accumulation • Simple to use • Not a “legal” record • Dose range device dependent
    15. 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. 16. Dose Limits
    17. 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. 18. 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
    19. 19. Occupational Dose Limits NRC / 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
    20. 20. Occupational Dose Limits NRCP 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
    21. 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. 22. 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
    23. 23. Dosimetry Reports
    24. 24. Expected Doses from Radiography Sources
    25. 25. 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

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