RADIATION PROTECTION Presented by Rose Aehle RT (R,M) MS Program 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 • 2007 ARRT REGISTRATION HANDBOOK • The College of St. Catherine, Development Testing Program for Radiography • PLEASE TURN ALL CELL PHONES TO VIBRATE MODE LD 50 LD 50/60 THE AMOUNT OF RADIATIONTHAT WILL CAUSE 50% OF EXPOSED INDIVIDUALS TO DIE WITHIN 60 DAYS WHAT THE REGISTRY WANTS YOU TO KNOW (2007 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 Line 2 Threshold is assumed, response expected at lower doses Response to exposure is directly proportional Cataractogenesis 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 FRACTIONATION How to read a nonlinear threshold dose response curve PROTRACTED DOSE Death/ Repair Damage/eradication of abnormal cells Repair •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 ???????????????????????????? College of St. Catherine ANSWERS D C 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 • LET - SPARSELY IONIZING RADIATION • GAMMA AND X-RAY • LOW LET OF 3 KEV 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 •number assigned to weighting factor different types of ionizing radiation. Dependent of the LET of particular radiation •Wt –Tissue weighting factor •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 Radiosensitivity based on Wt factors What is more radiosensitive? • CNS or GI? • Rectum or Small bowel? • Erythoblasts or Myelocytes? • red bone marrow or gonads? • Adult or elderly? • Lung or thyroid? 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 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 _____________ SOMATIC EFFECTS • STOCHASTIC aka PROBALISTIC effect • NONSTOCHASTIC aka Deterministic Effect • SOMATIC •Short Term •LONG TERM •ARS •THOSE EFFECTS THAT CAN –Hemopoietic (BONE BE DIRECTLY RELATED TO MARROW SYNDROME) HIGH DOSE OF RADIATION 100-1000 RAD ARE CLASSIFIED AS –25 RADS CAN DEPRESS NONSTOCHASTIC BLOOD COUNT •Cataract –Gastointestinal (600- •Reduced fertility 1000 RADS) –CNS (5000 RADS •Fibrosis Locally •Organ atrophy •Erythema 300-1000 RADS •Sterility •Epilation •LONG TERM STOCHASTIC •Delay/suppress CANCER menstruation 10 RADS EMBRYOLOGIC EFFECTS •Temporary sterility (both sexes – 200 RADS 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) Nothing b) Direct effect c) Indirect effect d) All of the above HIGH LET is associated with which effect? a) No effect b) Direct effect c) Indirect effect d) Radiolysis of water The following is true regarding indirect effect I) DNA is impacted by free radicals II) Some free radicals may chemically combine to form hydrogen peroxide III) DNA is directly struck by radiation IV) The minority of the damage to body is caused by indirect effect a) I only b) I and II only c) I, II and III only d) 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? •TRUE •5 mSv for the period of pregnancy •500 mrem for the period of pregnancy •TRUE •0.5 mSv per month •0.05 mrem per month •TRUE •Two badges •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 FLUOROSCOPY WHERE 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 PROTECTION Let’s keep safe! THE ENVIRONMENT •CONTROLLED AREA •Badged personnel •OCCUPANCY FACTOR •Who,what is where •UNCONTROLLED •Everyone else! AREA •USE FACTOR •% of time primary beam is directed at a particular wall •WORKLOAD •# 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 2007!!!!!