HEALTH PHYSICS

TERMS l RAD (Gy) l mRad l R l mR l Rem l ALARA l NCRP

mR/mAs l mAs=# of x-rays in useful beam=radiation quantity l Radiation=intensity of radiation- mR l I 1 =mAs 1 I 2 =mAs 2 As mAs increase, so does mR

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

HISTORICAL FACT l Clarence Daly-First American fatality from radiation\ l Thomas Edison’s assistant l Thomas Edison is credited for discovering….. l 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 l Exposure as short as possible l Dose to patient/occupational worker directly related to duration of exposure l Exposure = Exposure rate X time l Fluoro-Radiologists trained to turn switch on and off l 5 minute reset button

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

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

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

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

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

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

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

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

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

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

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

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

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

l 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. l Nearly IMPOSSIBLE for fetus to receive any where close to the allowed 500 mrem

MANAGEMENT PRINCIPLES l Employee handbook l New employee training l in-service training l counseling