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HEALTH PHYSICS

HEALTH PHYSICS. TERMS. RAD (Gy) mRad R mR Rem ALARA NCRP. mR/mAs. mAs=# of x-rays in useful beam=radiation quantity Radiation=intensity of radiation-mR I 1 = mAs 1 I 2 =mAs 2 As mAs increase, so does mR. Try this problem.

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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. DOSE LIMITS • NCRP • DL FOR VARIOUS ORGANS AS WELL AS WHOLE BODY FOR OCCUPATIONAL EXPOSURE • NOT DETERMINED FOR PATIENT

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

  15. 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

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

  17. 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

  18. RADIATION AND PREGNANCYBushong, pgs 607-609 • Time dependence • first 2 weeks of pregnancy-resorption and termination of pregnancy • 2nd week to 10th week period of major organogenesis=possible congenital abnormalities • 2nd and 3rd trimesters, responses above are unlikely. Malignant disease during childhood a likely response. This also possible with exposure in 1st trimester • Responses likely only with high rad doses (above 25 rad)

  19. DOSE DEPENDENCE • No responses at less than 25 rad • .1% of conceptions resorbed at 10 rad • 1% increase (of the 5% chance) is congenital abnormalities-10 rad • Exposure in 1st trimester childhood malignancy risk is 5-10 • drops to 1.4 in third trimester • Overall risk with fetal dose is 1.5 or 50% increase over natural occurring incidence

  20. The Pregnant Patient • Never knowingly take x-rays of patient without documented decision • Careful collimation. • High kVp • Elective booking • Patient questionaire • Posting

  21. All female employees should be made aware of pregnancy policy in writing upon start of employment Notify supervisor DL should not exceed 5mSv during pregnancy Most radiographers get 1mSv per year (100 mrem) Baby monitor THE PREGNANT RADIOGRAPHERBushong 625

  22. Under lead apron, dose at waist level will be 10% less than collar dose and of that 10%, dose of fetus would be 30% less than skin dose to abdomen. • Nearly IMPOSSIBLE for fetus to receive any where close to the allowed 500 mrem

  23. MANAGEMENT PRINCIPLES • Employee handbook • New employee training • in-service training • counseling

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