RADIATION PROTECTIONPresented by Rose Aehle RT (R,M) MSProgram Coordinator, Montgomery College

REFERENCES

• Bushong Radiologic Science for Technologists, Eighth Edition

• Ehrlich, Patient Care in Radiography, Sixth Edition

• Callaway, Mosby’s Comprehensive Review of Radiography

• Saia, Lange Q & A Radiography Examination, 6th Edition

• Sherer, Radiation Protection in Medical Radiography, Fifth Edition

• 2008 ARRT REGISTRATION HANDBOOK• The College of St. Catherine, Development

Testing Program for Radiography•

PLEASE TURN ALL CELL PHONES TO VIBRATE MODE

WHAT THE REGISTRY WANTS YOU TO KNOW (2008 ARRT handbook)

BIOLOGIC ASPECTS OF RADIATION

Dose response curves (Sherer)

Line 1

No level of radiation can be considered safe.

Response to exposure is directly proportional

Diagnostic imaging

Line 2

Threshold is assumed, response expected at lower doses

Response to exposure is directly proportional

Cataractogenesis

Radiation Therapy

BIOLOGIC ASPECTS OF RADIATION

Dose response curves (Sherer)

Line 3

Non linear (sigmoid or hypothetical sigmoid) dose response

DIAGRAM B

Non linear, threshold dose response used in radiation therapy

BIOLOGIC ASPECTS OF RADIATION

Damage/eradication of abnormal cells

Repair

Death/ Repair

How to read a nonlinear threshold dose response curve

FRACTIONATION

A fraction of a dose of ionizing radiation given over a period of time

PROTRACTED DOSE

A low amount of ionizing radiation given continously

•Linear quadratic nonthreshold dose response curve•Risks associated with low dose levels of low LET radiations•Stochastic somatic and genetic effects• “Leukemia, breast cancer and heritiable damage assumed to follow this curve”• Sherer

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College of St. Catherine

ANSWERS

DC

LET, RBE, QF

• Which comes first?

• LET?RBE?

QF?

• LET – AMOUNT OF ENERGY DEPOSITED BY RADIATION PER UNIT LENGTH OF TISSUE TRAVERSED calloway

• RBE- QUANTITATIVE MEASUREMENT OF BIOLOGIC EFFECT

• QF – NUMERIC UNIT GIVEN TO RADIATION BASED ON RBE TO DETERMINE REM

Facts about LET

• SPARSELY IONIZING RADIATION• GAMMA AND X-RAY• LOW LET OF 3 KEV per micrometer

OR LESS – ARE PENETRATING– INTERACT RANDOMLY ALONG ITS

TRACK (STOCHASTIC)

• AS LET INCREASES SO DOES RBE• HIGH LET

– LOW PENETRATION– SLOW MOVING – Direct Effect

Effective dose (E)=Wr X Wt x absorbed dose•Wr -Radiation weighting factor

•Wt –Tissue weighting factor

•number assigned to different types of ionizing radiation. Dependent of the LET of particular radiation

•Tissue radiosensitivity of irradiated material

FACTS ABOUT RBE• DOSE OF STANDARD RADIATION NECESSARY TO PRODUCE A

GENETIC EFFECT--------------------------------------------------------------------

DOSE OF TEST RADATION NECESSARY TO PRODUCE THE SAME EFFECT

• STANDARD RADIATION IS TYPICALLY 250 kVp (Bushong has a range of 200 – 250 kVp)

• Test radiation can range for x-rays to other types of ionizing radiation

• RBE for x-rays is one• Higher LET’s have Higher RBE = Higher QF

WT factors -which is more radiosensitive?

What is more radiosensitive?• Stomach or bladder?• Gonads or red bone marrow?• Colon or breast?• Thyroid or skin?

FACTS ABOUT QF

• REM IS CALCULATED BY MULTIPLYING THE QF OF A PARTICULAR TYPE OF RADIATION X RAD

• QF FOR X-RAYS IS 1• THEREFORE ONE RAD OF EXPOSURE

TO X-RAY = ONE REM• QF FOR ALPA IS 20

– HIGH LET– SLOW MOVING– LOW PENETRATION

• THEREFORE ONE RAD OF EXPOSURE TO ALPHA = 20 REMS

LD 50

LD 50/60

THE AMOUNT OF RADIATIONTHAT WILL CAUSE 50% OF EXPOSED INDIVIDUALS TO DIE WITHIN 60 DAYS

WHAT DOES THE LAW OF BERGONIE AND TRIBONDEAU SAY Re RADIOSENSITIVITY?

•Stem cells are_____________•Mature cells are ____________•Cells with _________metabolic and ___________mitotic activity are radiosensitive•Cells which are differentiated are _____________

•Radiosensitive

•Radioresistent

•High/high

•Radioresistent

SOMATIC EFFECTS

• STOCHASTIC aka PROBALISTIC effect

• NONSTOCHASTIC aka Deterministic Effect•

SOMATIC•Short Term

•ARS–Hemopoietic (BONE MARROW SYNDROME) 100-1000 RAD–25 RADS CAN DEPRESS BLOOD COUNT–Gastointestinal (600-1000 RADS)–CNS (5000 RADS

Locally•Erythema 300-1000 RADS•Epilation•Delay/suppress menstruation 10 RADS •Temporary sterility (both sexes – 200 RADS

•LONG TERM•THOSE EFFECTS THAT CAN BE DIRECTLY RELATED TO HIGH DOSE OF RADIATION ARE CLASSIFIED AS NONSTOCHASTIC•Cataract•Reduced fertility•Fibrosis•Organ atrophy•Sterility

•LONG TERM STOCHASTIC

CANCEREMBRYOLOGIC EFFECTS

CARCINOGENESIS

• The cancer that can be ALMOST classified as radiounique is leukemia

• Has a short latency period• Has a linear nonthreshold dose response

curve• Epidemiologic studies indicate a higher

incidences in leukemia after large exposures

• Radium watch dial workers –bone ca• Uranium miners – lung ca• Early medical radiation workers –

leukemia• Thymus gland treatment – thyroid ca• Children of Marshal Island – thyroid ca• Atomic bomb survivors –

leukemia/breast, lung and bone

WHAT CAN HAPPEN WHEN IONIZING RADIATION HITS THE CELL?

a) Nothingb) Direct effectc) Indirect effectd) All of the above

HIGH LET is associated with which effect?

a) No effectb) Direct effectc) Indirect effectd) Radiolysis of water

The following is true regarding indirect effect

I) DNA is impacted by free radicalsII) Some free radicals may chemically

combine to form hydrogen peroxide

III) DNA is directly struck by radiationIV) The minority of the damage to

body is caused by indirect effecta) I onlyb) I and II onlyc) I, II and III onlyd) All of the above

TARGET THEORY

A) THE DNA IS DIRECTLY HIT B) ONLY SOME CELLS HAVE MASTER

MOLECULES THAT DIRECT CELL ACTIVITY

C) ONE CANNOT DETERMINE IN ANY CELL DEATH IF THE DEATH WAS RESULT OF DIRECT OR INDIRECT EFFECT

EMBRYONIC AND FETAL RISKS

• Spontaneous abortions during first 2 weeks of pregnancy-- 25 RAD or higher

• 2nd week to 10th week – major organogenesis –IF radiation is high enough can cause congenital abnormalities

• Principle response after that may be malignant disease in childhood

PREVENTING ACCIDENTAL IRRADITATION TO PATIENT

• FIRST TWO MONTHS, CRITICAL• 10 DAY RULE• ELECTIVE BOOKING• QUESTIONAIRE• POSTING

IF A PREGNANT PATIENT MUST BE X-RAYED

• TIGHT COLLIMATION• HIGH KVP• SHIELDING• REDUCED # OF IMAGES • MAKE SURE TO CHECK WITH YOUR

SUPERVISOR AND BE AWARE OF THE SITE’S PROTOCOL

GSD

• GENETICALLY SIGNIFICANT DOSE• 20 mrem estimated dose• Equivalent dose to the

reproductive organs received by every human would cause the same genetic injury as the actual dose received by individual population members

The pregnant radiographer

•WHICH OF THE FOLLOWING IS (ARE)

TRUE?•5 mSv for the period of pregnancy•500 mrem for the period of pregnancy•0.5 mSv per month•0.05 rem per month•Two badges

•TRUE

•TRUE

•TRUE•TRUE

LET’S PICK UP THE PACE NOW!KEEP THE PATIENTS SAFE!!!

WHAT KIND OF EXPOSURE FACTORS ARE BEST FOR PATIENTS?

• NAME FACTORS TO KEEP PT DOSE DOWN• AS SID increases, what happens to the

intensity? What do we adjust and do we increase or decrease this adjustment?

• Which of the following impacts PT dose?– Inherent filtration?– Added filtration?– SID?– Focal spot size?– Screen speed?

WHAT GIVES HIGHEST CONTRAST BUT INCREASES PATIENT DOSE?

• COMPTON?• CHARACTERITIC?• BREMSSTRAHLUNG?• PHOTOELECTRIC?

DO GRIDS DECREASE PATIENT EXPOSURE?

MINIMIZING PATIENT EXPOSUER

• SHIELDING– Gonadal shielding females reduces

gonad dose by 50%– Gonadal shielding males reduces

gonad dose by 95%– Flat, shadow shields

• COLLIMATION– DID YOU KNOW THAT THERE ARE A

HIGHER SET OF LEAD SHUTTERS PLACED NEAR THE X-RAY TUBE WINDOW TO ABSORB OFF-FOCUS RADIATION?

• FILTRATION– INCREASED FILTRATION (HVL)

INCREASES THE AVERAGE BEAM ENERGY

– No filtration on a 70 kVp tube (0-70) would produce an average energy of 35 kVp

– However, if you filter out the lower energies (30-70 kVp) is 50 kVp

– Inherent– Added– _________is required for machines

operating at 70 kVp

HVL

• How many HVL’s are required to reduce the intensity of the beam to less that 15% of its original value

• A) 2• B)3• C)4• D)5

FLUOROSCOPYWHERE SCATTER ALWAYS MATTERS!

READING NOMOGRAMS

•What kind of info do you need?

•From Appleton and Lange•What is the approximate patient ESE from an AP projection of the abd. made at 105 cm, 70 kVp, 300 mA, 0.2 sec (60 mAs)and 2.5 mm AL total filtration

SCATTER STATS

• Each time the x-ray beam scatters, its intensity at 1 meter from the scattering object is one thousandth of its original intensity

• or it decreases 1000 times!!!! • Or 1/1000 or • 0.1%

FLUOROSCOPY

• PULSED (DF)• X-RAY TUBE OPERATES IN

RADIOGRAPHIC MODE WHICH MEANS USING TECHNICAL FACTORS THAT ARE USED FOR OVERHEAD EXAMS

• HOWEVER• THE TIME REQUIRED TO REACH THE

SELECTED MA AND KV (INTERROGATION TIME) AND THE TIME FOR THE X-RAY TUBE TO BE SWITCHED OFF (EXTINCTION TIME) IS LESS THAN 1 MS

• THEREFORE IN DR FLUORO A 5 MINUTE STUDY WILL RESULT IN A PATIENT DOSE OF 10 RAD VS 20 RAD FOR A CONVENTIONAL FLUOROSCOPY STUDY

Conventional fluoroscopy

• mA less than 5• Use of magnification mode

increases patient exposure

All types of fluoro

• Intermittent fluoro• Field size• Focus to table distance (15”

stationary, 12” mobile

PERSONNEL PROTECTIONLet’s keep safe!

THE ENVIRONMENT

•CONTROLLED AREA

•OCCUPANCY FACTOR

•UNCONTROLLED AREA

•USE FACTOR

•WORKLOAD

•Badged personnel

•Who,what is where

•Everyone else!

•% of time primary beam is directed at a particular wall •# of x-ray exams per week

• Primary barrier• 7 feet, 1/16 inch of lead

• Secondary barrier• Extend to ceiling• 1/32 inch of lead

Which of these regulations are accurate? • DL for eye is 50 mSv?• Cumulative whole body is 10mSv x age?• Leakage radiation – 100 mR/hr at 2 meters?• Lead aprons at 0 .25 mm pB equivalent?• ESE in 10R/min in fluoro?• Exposure cord on portable must be 1 meter

long?• Pregnant radiographer DL for fetus is 500

mrem for period of pregnancy?• The public exposure DL is 100 mrem per

year?• Bucky slot cover and protective curtain,

minimum of 0.5 pB equivalent?

FINALLY!!!

• ALARA• CARDINAL RULES OF PROTECTION• PERSONNEL MONITORS

– TLD’S VS OSL VS. FILM BADGES VS DOSIMETERS

– Lithium fluoride vs aluminum oxide vs x-ray film vs.gas

• INVERSE SQUARE LAW WITH EXPOSURE RATE

• If a radiographer receives 25 mR standing 3 feet from the source for one hour how much would he receive if he stands 2 feet from the source at 20 minutes?

• 25mR 2 feet squared X 3 feet squared• 25 mR 4 feet x 9 feet• 4 x = 225• X = 56 mR per hour• 20 minutes/60 minutes = .33• 56 mR x .33 = 18.48 mR at two feet for

20 minutes

SEE YA!!! GOOD LUCK TO ALL THE GRADUATES OF 2012!!!!!