RADIATION PROTECTION
Presented by Rose Aehle RT (R,M) MS
Program Coordinator, Montgomery College
REFERENCES
• Bushong Radiologic Science for
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•
•
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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
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
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
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
•ARS
–Hemopoietic (BONE
MARROW SYNDROME)
100-1000 RAD
–25 RADS CAN DEPRESS
BLOOD COUNT
–Gastointestinal (6001000 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
CANCER
EMBRYOLOGIC 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) Nothing
b) Direct effect
c) Indirect effect
d) All of the above
HIGH LET is associated with which
effect?
a)
b)
c)
d)
No effect
Direct effect
Indirect effect
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?
•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
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
AREA
•Everyone else!
•USE FACTOR
•% of time primary
beam is directed at a
particular wall
•# of x-ray exams per
week
•WORKLOAD
• 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?
•
•
•
•
•
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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 2011!!!!!