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 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

DISTANCE

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

DOSE LIMITS

NCRP DL FOR VARIOUS ORGANS AS

WELL AS WHOLE BODY FOR OCCUPATIONAL EXPOSURE

NOT DETERMINED FOR PATIENT

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

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

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)

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

The Pregnant Patient

Never knowingly take x-rays of patient without documented decision

Careful collimation. High kVp Elective booking Patient questionaire Posting

THE PREGNANT RADIOGRAPHERBushong 625

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

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

MANAGEMENT PRINCIPLES

Employee handbook New employee training in-service training counseling