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 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 PHYSICS PROVIDING 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

DISTANCE Isoexposure lines exposure areas calculated at waist level 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

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