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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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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 • I1 =mAs1 I2 =mAs2 As mAs increase, so does mR
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
HISTORICAL FACT • Clarence Daly-First American fatality from radiation\ • Thomas Edison’s assistant • Thomas Edison is credited for discovering….. • Fluoroscopy
HEALTH PHYSICSPROVIDING RADIATION PROTECTION FOR OCCUPATIONAL WORKERS AND TO THE PUBLIC
CARDINAL PRINCIPLES OF RADIATION PROCEDURES DESIGNED TO MINIMIZE RADIATION EXPOSURE TO PATIENTS AND PERSONNEL
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
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
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
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
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)
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
RT effective dose 10% of monitor dose…why?
Radiologic Terrorism • Rescue and medical emergencies priority over radiologic concerns • RED • RDD • IND
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
PUBLIC EXPOSURE • Annual 5mSv per year (500mrem) • 1mSv (100mrem)non-RT hospital workers • 1mSv is unit physicists use for thickness in protective barriers
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