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HEALTH PHYSICS

HEALTH PHYSICS

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HEALTH PHYSICS

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  1. HEALTH PHYSICS

  2. TERMS • RAD (Gy) • mRad • R • mR • Rem • ALARA • NCRP

  3. mR/mAs • mAs=# of x-rays in useful beam=radiation quantity • Radiation=intensity of radiation-mR • I1 =mAs1 I2 =mAs2 As mAs increase, so does mR

  4. Try this problem • If the exposure factors of 85 kVp, 400 mA and .12 sec yield an output of 150mR, what is the mR/mAs? • 150mR/48 = 3.12 mR/mAs

  5. HISTORICAL FACT • Clarence Daly-First American fatality from radiation\ • Thomas Edison’s assistant • Thomas Edison is credited for discovering….. • Fluoroscopy

  6. HEALTH PHYSICSPROVIDING RADIATION PROTECTION FOR OCCUPATIONAL WORKERS AND TO THE PUBLIC

  7. CARDINAL PRINCIPLES OF RADIATION PROCEDURES DESIGNED TO MINIMIZE RADIATION EXPOSURE TO PATIENTS AND PERSONNEL

  8. TIME • Exposure as short as possible • Dose to patient/occupational worker directly related to duration of exposure • Exposure = Exposure rate X time • Fluoro-Radiologists trained to turn switch on and off • 5 minute reset button

  9. TRY THIS PROBLEM • If a certain exam is calculated to have an exposure rate of 225mR per hour, what is the total exposure per 36 minutes? • X(exposure) = 225mR x 36/60 • x = 135 mR

  10. As distance increases, radiation intensities to the occupational worker and other personnel decreases X-ray tube target is considered a point source of radiation Scatter from patient is considered an extended area source Isoexposure lines exposure areas calculated at waist level patient an extended source of radiation DISTANCE

  11. SHIELDING • Thickness or amount of shielding can be estimated if the HVL or TVL of barrier is known • TVL=tenth value layer • 1 TVL = 3.3 HVL • See questions on page 553

  12. Effective dose • Partial body exposure • Risks are based on whole body exposure • Stochastic response is based on effective dose which is calculated as • The weight of the dose x the weight of the tissue (NCRP Report 116)

  13. DL FOR OCCUPATIONAL PERSONS SHOULD NOT EXCEED SPECIFIED LIMITS • Dose limits (occupational) • Current DL is 100mRem (mSv) per week • Annual = 50mSv (5000mrem or 5 rem) • eye = 150mSv(15000mrems) • organs= 500 mSv (50,000 mrems) • pregnancy = 5mSv(500 mrem) not to exceed .5mSv per month • cumulative 10 mSv x age in years

  14. RT effective dose 10% of monitor dose…why?

  15. Radiologic Terrorism • Rescue and medical emergencies priority over radiologic concerns • RED • RDD • IND

  16. Intro to radiation protection • Bushong pg 516, figure 33-4 • DL is based on linear nonthreshold dose response relationship • E = Wr x Wt • LET • Conversion factor of .3 applied to collar-monitor value

  17. PUBLIC EXPOSURE • Annual 5mSv per year (500mrem) • 1mSv (100mrem)non-RT hospital workers • 1mSv is unit physicists use for thickness in protective barriers

  18. MISCELLANEOUS DL NOTES • Student radiographers under the age of 18 may receive no more than 1 mSv during the duration of their educational activities • There is a movement underway to lower DL for occupational workers to 20 mSv