Download Radiation Exposure

9/2/2011
WHAT YOU DON’T SEE
CAN HURT YOU
DR. KENNETH WARD
CHILDREN’S HOSPITAL
DEPARTMENT OF RADIOLOGY
or
DEPARTMENT OF POTENTIALLY DANGEROUS INVASIVE PARTICLES OF
NUCLEAR MATTER OR ELECTROMAGNETIC WAVES THAT PENETRATE
YOUR BODY AND MAY KILL OR MAIM YOU IN AN UNSUSPECTED AND
INSIDIOUS MANNER
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INSPIRATION
Radiation risk to children from computed
tomography;; PEDIATRICS Vol 120 No 3, Sept.
tomography
2009
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RESOURCES
Biological Effects of Ionizing Radiation (BEIR)
United Nations Subcommittee on Atomic
Radiation (UNSCEAR)
American College of Radiology (ACR)
Society of Pediatric Radiology (SPR)
Medical Radiation Biology: Pizarello, Witcofski;
Lea and Feiberger 1982
Radiation Risks in Medical Imaging:
Imaging: Whalen and
Balter; Yearbook Medical Publishing 1984
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FEAR OF THE UNKNOWN
What will happen to
me?
What will happen to
my offspring?
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REAL RISK OF MEDICAL
IMAGING
Difficult to define
“Cannot see, smell or
taste radiation”
Detect with ion
ion-chambers
– Geiger
Geiger--Muller
Scintillation detectors
– Glows when exposed
DNA mutation
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IONIZING RADIATION
Radiation
– Energy in transit
Radioactivity
– Characteristics of
various materials to
emit ionizing radiation
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TYPES OF RADIATION
Alpha
– Helium atom (2N 2P)
– Heavy metal decay
Uranium, thorium,
radium
di
– Travels short distance
– Strong interaction
– Easily stopped
Paper,
Paper skin,
skin clothes
– Dr. No, Indiana Jones
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TYPES OF RADIATION
B t decay
Beta
d
– Electron from unstable nuclei
Elements below stable line on
periodic table
– Nuclear reactors
– Travel farther
Several meters
– Interact less
– Stopped by light metals or
plastic
Aluminum filters
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TYPES OF RADIATION
Cerenkov radiation
High energy betas
that travel through
water from fuel
reactors
– Blue glow
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TYPES OF RADIATION
Gamma rays
Gamma
– Electromagnetic radiation
– From excited nucleus
Tc 99m
Cs 137 (calibrate nuclear
q p
)
equipment)
– High energy light or microwave
– No mass or charge
– Collides with electrons in shells of
atoms
– Lose little energy
– Travel long distance
Hundreds of meters
Stopped by dense metals,
concrete, earth
Pass right through people!
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TYPES OF RADIATION
X-RAYS
– Conrad Roentgen 1895
– By
By--product of collision
between electrons and
heavy metal (tungsten)
– High energy
– Travels further
– Dose reduced by ½ for
every double in distance
away from source
– Stopped by heavy metals
(lead)
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TYPES OF RADIATION
Neutron
– Neutral particle
– Mass of proton
Weak interaction
– “Clean bomb”
Deep penetration
Nuclear power
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RADIATION UNITS
Roentgen
(coulombs/kg)
– Gamma or xx--rays in air
Rad: Radiation
Absorbed Dose
– Gray = 100 rads
Rem: biological effect
– Sievert = 100 rem
Gray x’s quality factor
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RADIOACTIVITY IN NATURE
Primordial
– Before the creation of the earth
Cosmogenic
– Result of cosmic ray interaction
Human produced
– Enhanced or formed due to human
actions
– Minor
Radionuclides found in air, water,
and soil
Building materials
– Brick, concrete
Even in us!!!!
Every day we ingest and inhale
radionuclides
– Radon
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SOURCES
SOURCE
AVG ANNUAL EFFECTIVE DOSE
EQUIVALENT (MREM)
Inhaled
200
Internally deposited
39
Terrestrial
28
Cosmic
27
Natural
300
Artificial
60
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You are what you eat!
Bad
B d ffood
d
–
–
–
–
–
–
Banana
Brazil nuts
Carrots
White potatoes
R d meatt
Red
Lima beans
Good food
– Water
– Beer (HOORAY!)
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Damned if you do
Building materials
– Brick
– Granite
– Cement
– Concrete
– Wallboard
Nuclear reactors
Waste
Smoke detectors
Luminous watches
TV tubes
Artificial teeth
Optical
p
g
glass
Tobacco smoke
Radon
Cell phones
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Damned if you don’t
B ildi materials
Building
t i l
– Wood
Gamma rays penetrate
Cosmic radiation
– Absorbed by atmosphere
– 27 mrem/yr
– Doubles every 6,000 feet
Denver, Mexico City
Flying NYNY-Paris @ 36,000
feet
– 3.1 mrad
– Effect less at equator
Geomagnetic field effect
on atmosphere
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Terrestrial radiation
High background
radiation
Black sand (monzanite)
– 5 mrad/hr
CXR 50 mrad
– 400 x’s U.S. natural
background radiation
Brazil
India
China
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Terrestrial
Brazil
– Hill high in thorium
Plants can produce xx-ray if placed
on photographic film
Oklo natural nuclear reactor
– 1972 – Western African Republic
of Gabon at Oklo
– Critical reactor 1.7 billion years
y
ago
– Released 15,000 megawatts
megawatts-years of power
– Consumed 6 tons of uranium
– Natural uranium
– Ground water supply
– Lack of neutron absorbing poisons
– By
B -products
Byd t limited
li it d power ((xenon,
neodynium)
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Biological effects
BEIR V
V, N
National
ti
lR
Research
h
Council
Report on health effects of low
levels of ionizing radiation
“In areas of high background
radiation, increased frequency
of chromosome aberrations
were noted, consistent with
radiation workers and persons
exposed at high dose levels.
No increased frequency of
cancer was detected.”
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RELATIVE RADIATION LEVELS
SOURCE
# CXR / YR
Natural
50
50--100
Diagnostic
0.1
0 11-500
Nuclear imaging
50
50--1,000
Start of acute radiation
syndrome
Radiation therapy
30,000 CXR / day
100,000
100,000--1,000,000 CXR
/ wk
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RISK
Stochastic risk
– Probability of occurrence in
a population is proportional
to radiation dose received
by the total population
Ex: Lottery ticket
– Few win
– Rest of population
unaffected
Radiation odds favor no
injury to the individual
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Estimated loss of life expectancy
Lifestyle
Loss in days
Unmarried male
3,500
Smoker – male
2,250
Unmarried female
1,600
Smoker – female
800
Dangerous job
300
MVA
207
Alcohol
130
Accidents – home
95
Average job
74
Radiation job
40
Accident – pedestrian
37
Safest job
30
Natural radiation
8
Medical xx-rays
6
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RELATIVE RISKS
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Lifestyle expectancy
ACTION
LOSS IN MINUTES
Buying a small car
7,000
Coast to coast drive
1,000
Coast to coast flight
100
Smoking a cigarette
10
Calorie rich dessert
50
Non--diet soft drink
Non
15
Diet soft drink
0.15
Crossing street
0.4
Not fastening seatbelt
0.1/mile
1 mrem of radiation
1.5
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OH NO!!!
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What are YOU thinking?
We’re all going to die!
What’s the point of living!
Just tell me something to make me feel better about
myself!
I can’t believe I paid for this!
I should
h ld b
be att Di
Disney W
World!
ld!
No! Wait! Disney is far too risky
…and then there’s the drive there and my car is too
small
… and the calorie rich desserts after a long day on the
rides!
id !
OH NO! THE RIDES ALONE COULD KILL ME! I MIGHT
AS WELL STAY HOME!
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Why are you here?
Let’s get a grip on the
real risk of medical
radiation exposure.
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ACUTE RADIATION EFFECTS IN MAN
Total dose received < 1 day
Non--stochastic effect = everyone affected
Non
Whole dose mrad
Critical tissue
Comment
10,000,000
CNS
Death < 1 day
1,000,000
GI
Death ~ 1 wk
600,000
Bone marrow
Possible death ~ 1 mo
100,000
Regional
Rad Tx max
100,000 total body
Bone marrow
WBC suppression
10,000
Fetus
Increased congenital abnormality
animals
1,000
Bone marrow
Possible measurable increase
leukemia adults
1,000
Fetus
Possible statistical increase
tumors
150
Whole body
Bone scan dose
200
Limited region
KUB
Rad Tx
Medical Tx not required < 20,000 rads
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BIOLOGICAL EFFECTS
Cancer induction
– Atomic bomb survivors
Fetal effects
– 5 Rads
– Rapid cell division
3 divisions
– Pre
Pre--implantation
Fetal death
– Major organogenesis
Congenital
abnormality
– Fetal growth
Cell depletion
p
Growth reduction
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BIOLOGICAL EFFECTS
GSD – genetically significant dose
– Fraction of medical radiation that can have genetic
impact
– Presumed impact on entire population
– Cannot be applied to individual
Doubling dose
– Radiation that induces a mutagen rate that is twice
the spontaneous mutation rate
– ~156 rads (BEIR, UNSCEAR, atomic bomb survivors)
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Detection of Radiation Induced
Cancers
Indistinguishable from those
occurring naturally
High background rate makes
detection difficult
– Lifetime risk of fatal cancer
16%
Long latent period
Effect of disease as opposed
to the Radiation Tx
No effective control population
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FERTILITY EFFECTS
Permanent sterilizing doses
– 500 rads acute exposure
– 1500 fractionated over several
days
Male
– Impaired fertility acute testicular
dose 100 rads
– 90 day repair
Female
– Acute ovarian dose 300
300--400 rads
– Hi resistance of oocytes
– No repair cycle
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PREGNANCY AND RADIATION
H
Harmful
f ld
dose still
till unknown
k
Estimation of risk, decision to terminate
difficult
4-6% natural rate of congenital defects
Increased risk of congenital defects below
10 rads exposure to fetus negligible
Greater fetal vulnerability 10 day through
10thh week
Risk negligible < 5 rads, high > 10 rads
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TEST !
Call from local MD
Patient had Thyroid scan
Was asked if she was pregnant
Said no
Missed her period
Pregnant! 1st 14 days!
What to do?
Call physicist!
Estimate risk based on all this data!
Advise patient
Saving grace – organogenesis had not yet started
No thyroid to affect in fetus.
Baby born intact!
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TEST 2
Same story
Third trimester pregnancy
Baby born absent thyroid tissue
On Synthroid for entire life
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TEST 3
Hematuria
18 yo
Asked if could be pregnant
Said yes
Tested
Lab called with negative result
IVP started
Scout film
1st post
post--injection
Lab called back with positive result!
Lab error, wrong patient
Study stopped
What to do?
Call physicist!
Estimate risk!
Advise patient.
Baby born with teratoma of CNS
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What to do with the fertile female?
Hospital policy
National standards
Establish appropriate age related actions
Mandatory testing above age 13 for high
risk procedures
– Anesthesia
– Chemotherapy
– I-131 thyroid therapy
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Case of the best intentions
Weird radiology resident
Mother and 8 y/o daughter
Fluoro case
Asked if she could be pregnant
Said yes
Mother attacked resident
Resident rescued
Asked her again
Said yes
Tested positive
Problems at home
Resident eventually transferred to Psychiatry
Should have gone to the casino
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MAXIMUM PERMISSIBLE DOSE (MPD)
NRCP dose limits
Maximum permissible dose equivalent for
occupational exposure
Occupational
O
ti
l
– Annual 5 rem / yr
– Long term (Age minus 18) x 5 rems
Public
– 0.5 rems / yr
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RADIOLOGY PROCEDURES
I
Imaging
i area
D
Dose
mrads
d
E i l t CXR’
Equivalent
CXR’s
Ankle 3
3--view
1.5
1/14th
Chest--2 view
Chest
20
1
KUB
50
2.5
Bone scan
6200
310
PET scan
15,000
765
Fluoro VGUG
330
16
CT head
4000
200
CT chest
3000
150
CT abdomen
5000
250
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BEST TEST
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REGULATORY CONTROLS
E
Exposure
rate
t closely
l
l ffollowed
ll
db
by government,
t
with max exposure rate checked annually
– Fluoro = 1 rad / min tabletop max exposure
– Room closed until problem resolved
New technology
gy often not tightly
g y regulated
g
Push for image quality led vendors to increase
radiation in new digital cath labs to satisfy MD’s
– 10 rads / min
Legal case: ~50 minute interventional fluoro
case in new DR cardiac cath suite = skin burn =
500 rads total exposure = radiation Tx
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Why CT?
Disproportionately higher rate of radiation exposure from radiation
procedures
– Mettler et al, 2000
11% of procedures
67% of dose
# of indications and procedures increasingly rapidly
# of detector rows effectivelyy increases the amount of exposed
p
tissue to
radiation exposure during multimulti-slice scan
Wide range of techniques produce similar image quality
– CXR: small over
over--exposure produces significant change in film quality
Dose reduction of 5050-90% yields satisfactory image quality for children’s
imaging
Dose reduction of 5050-90% yields satisfactory image quality for children’s
imaging
Dose reduction of 5050-90% yields satisfactory image quality for children’s
imaging!!!
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SPIRAL MULTISLICE CT
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REDUCTION IN RADIATION
EXPOSURE (UNSCEAR)
Reduce # radiographs / patient
Reduce time and intensity of exposure
Use plain xx--rays, not fluoro
Use smallest field of view
Avoid gonadal exposure
Shield gonads
Properly train and supervise staff
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BE PREPARED!
LEAD UNDERWEAR
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ALARA
As Low As Reasonably
bl Achievable
hi
bl
IR suite precautions
– Tight collimation
– Pulsed fluoro
Unacceptable to many clinicians
– Last image hold
Avoids additional exposures
– Magnification only when necessary
– Appropriate shielding of personnel
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ALARA
CT
Avoid adult
techniques in children
Alter technique based
on body part
– Automatic on newer
machines
Scan only necessary
tissues
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PHYSICIAN RESPONSIBILITY
Clinician
– Communicate with the
radiologist to decide
whether CT is best test
– US, MR alternatives
Radiologist
– Create protocols and adjust
scanning techniques on the
basis of special
considerations in the
pediatric
di t i patient
ti t
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Tale of the Children’s CXR
25 years ago
ago, in a land far away
High film / screen combo
– Poorer resolution
– Dose reduced by 90%
Nobody complained
No interpretation errors
N d ffor hi
Need
high
h resolution
l ti
– Metastatic disease
– Bone trabeculae
Keep a few high resolution cassettes for special situations
Inquiring minds ask: Why aren’t your films as PRETTY as those
from other site?
B
Because
they
th are using
i adult
d lt hi
high
h resolution
l ti fil
films att th
the costt off 10
fold increase in radiation exposure, with no appreciable increase in
diagnostic acumen. That’s why!
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SUMMARY
Radiation is an essential component of medical imaging
Amount of radiation is lowlow-level
Cause and effect of lowlow-level radiation unknown, but
appears small
No direct connection between CT and cancer, so risks
estimated
Amount of radiation per CT varies, including protocols
and equipment
Pediatric protocols for pediatric patients
Potential benefit from diagnosis by CT appears much
greater than potential cancer risk
ALARA trained radiologists
THAT’S ME!
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LIFE’S LESSON
STARRING:
A bird in peril
A passionate French
doctor
The bird’s angry parents
Th wrath
The
th off an angry
mob
A daring rescue
The inevitability of
nature’s laws
D
Darwin
i rules
l
Grief and sorrow
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