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Radiation Risk
Fact vs Fiction
Disclosures
• No financial disclosures for myself or family
• No off label uses will be discussed
• One exception: I am a radiologist
– 25+ years selling xrays for a living
– Mortgages and college tuition still to pay
Radiation Risk
• Concept of Dose and Measurements
• Relative Risk related to age and gender
• Impact of Medical Imaging
Quiz 1
A. Cujo
B. Godzilla
C. Barney
D. None of the
above
Quiz 2
• Radiation induced carcinogenesis increases in
likelihood with dose. It is considered a
stochastic effect.
• True or False
– Current risk models for radiation carcinogenesis
assume that a lower limit of radiation exists below
which no risk of cancer is present?
– A. True
– B. False
Impact of Radiation
Exposure
• Stochastic and Deterministic Effects
– Deterministic Effects
• Severity increases with dose, effect is prompt
• Lower limit threshold exists
• Examples (erythema, infertility(3-6Sv), marrow
suppression)
– Stochastic Effects
•
•
•
•
•
Likelihood increases with dose, effect is delayed
Genetic Damage/Carcinogenesis
No threshold
Risk of lifetime death from 100mSv ~.8%
Examples (Leukemia…)
Dose Quantification
• Sievert vs other units of measurement
• Concept of Relative Dose
– Absorbed dose is used to assess the potential for biochemical changes in
specific tissues. [Unit is the milligray (mGy)]
– Equivalent dose is used to assess how much biological damage is
expected from the absorbed dose. (Different types of radiation have
different damaging properties.)[For diagnostic radiation: The equivalent
dose in milliSievert (mSv) = the absorbed dose in mGy.]
– Effective dose is used to assess the potential for long-term effects that
might occur in the future. Effective dose is a calculated value, measured
in mSv, that takes three factors into account:
• the absorbed dose to all organs of the body,
• the relative harm level of the radiation, and
• the sensitivities of each organ to radiation.
Risk of Radiation Effects
• Tissue dependent
– Slowly dividing cells less sensitive
– Marrow more sensitive than skeletal or neural tissue
• Age dependent
– Risk of carcinogenesis likely is reduced by half in
older adults compared with 30 y/o
– Risk in infants and young children is likely doubled
compared with young adult ( National Research Council. Health
risks from exposure to low levels of ionizing radiation. BEIR VII Phase 2.
Washington, DC: National Academies Press; 2006.)
Relative Organ Risk and Age
Graph shows estimated excess cancer mortality risk
according to age at time of exposure in a stationary
population, with U.S. mortality risk rates, that is exposed to a
radiation dose of 10 mSv (14). Data are averages between the
sexes.
Published in: "Estimated Radiation Risks Potentially
Associated with Full-Body CT Screening1“
Brenner and Elliston
Radiology Vol. 232, No. 3: 735-738
©RSNA, 2004
Risk of Exposure and AGE
The British Journal of Radiology, 81 (2008), 362–378
Relative Radiation Exposure
of Ct
• Background Radiation
– Cosmic
– Radon Gas (number one source for exposure)
– Annual exposure
• Man-made Radiation Exposure
– Diagnostic Imaging
– Contribution of CT
– Change over time
Quiz 3 “Mothra”
Mothra’s Weapons included
A. Poisonous Fangs
B. Hurricane Winds
C. Atomic Blast
D.None of the above
Quiz 4 Radiation Annual
Dose
• The Majority of the annual average dose of
radiation received by the US population comes
from:
– A. Residua of atomic bomb tests and nuclear
reactor accidents
– B. Cosmic Radiation
– C. Medical Imaging
– D. Radon Gas
U.S. Annual Dose Changing
due to Medical Imaging
Relative Contributions of
Radiation U.S. 2006
Strategies to Minimize Dose
• Technical parameters in CT can be adjusted
– GHS CT scanners are optimized to minimize
dose
– Scanned areas should be limited to that which is
necessary
• Alternative Diagnostic Strategies
– Image Wisely
– ACR Appropriateness Criteria
Clinical Vignettes
• Utilize the average reported doses for common
radiological exams
• Online Calculator: radiation induced
carcinogenesis is utilized (xrayrisk.com)
• Examples:not intended to be a detailed
evaluation of clinical decision making
• Goal is to give a sense of the magnitude of
impact in radiation induced carcinogenesis that
different imaging algorithms may have
Relative Risks of Alternative
Dx Strategies
• Liver Lesion Evaluation in 30 y/o female
– Biliary ultrasound identifies solid mass in liver of
otherwise healthy female with nonspecific RUQ
pain
– Recommendation for definitive imaging
suggested
• Multiphasic CT
• Liver MRI
Relative Risk of Radiation
from Liver CT
Relative Risk of Multiple
Liver CT’s for Lesion
Observation
Relative Risk of MRI for Cancer
Induction from Radiation
• No ionizing radiation is involved in MRI and
therefore the added risk of cancer induction is zero
SBS vs CTE vs MRE for
Crohn’s Disease 25y/o Male
MR Enterography is ZERO……and likely more useful information
than SBS
30 y/o Female with CP,
Cough and Hemoptysis
Modified Wells score = 1
Pleural Effusion Evaluation
CT vs Decub Xrays vs US
50 y/o Male
Ultrasound is ZERO, no ionizing radiation
20 y/o Male RLQ pain
CT vs Physical Exam
25 y/o Female Chest Pain after
Trauma and Normal CXR
1 more cancer case for every 900 patients managed this way
CT Utilization Optimization
• Radiation Risk
– Cancer induction risk is thought most likely proportional
to dose
– Younger pts and more rapidly dividing tissue is at
greater risk
• CT is leading source and current US Exp 2X prior
– CT is 25%
– Absolute risk is in range of ~1/150 to 1/2000
• Radon is number 2 source that can be mitigated
• Cost of CT to care is substantial ~1.3M/yr
Quiz 3 “Them”
Famous Actors as Cast Members
A. James Arness
B. Fess Parker
C. James Whitmore
D. Leonard Nimoy
E. All of the above
Quiz 4 Residential Radon
• Residential radon gas can be excluded as a
significant risk if:
– A. I have city water and no risk from well water
contamination
– B. My neighbors house was tested and all my other
neighbors are OK.
– C. My house was tested.
– D. My house is only 5 years old and has no
basement.
Radon
• Decay product of U-238 and Radium-226
• Risk in Uranium miners well established
• Residential Risk?
– RR = 1.1 (1.0-1.3)
– Smokers greater
US Radon Map
SC Radon Risk
Residential Radon
• Discovered by investigators of Stanley Watras
– Construction engineer at Nuclear Plant with no fuel
(PA)
– Set off alarm
– Radiation was from home
– 2,700pCi/L (max safe home levels 4 pCi/L)
• Peak Areas
– Appalachian Mountains
– Iowa, fertile soil of upper midwest from glaciation
The Discoverer of Residential
Radon
Quiz 7 “Matango”
A science research vessel
studying the aftermath of
radiation exposure is found
abandoned by a pleasure yacht
that becomes stranded. The
research vessel crew is:
A. Blood thirsty savages
B. Members of Greenpeace
C. Mutated into “Mushroom
People”
D. None of the above
Quiz 8 Fetal Radiation
• Diagnostic medical imaging exposure of the
fetus may likely:
– A. Improve future academic performance
– B. Double the risk of childhood malignancy
– C. Result in injuries visible at birth
– D. None of the above
News Article and Fetal Radiation
NCI sponsored
Included cases of xrays of abdomen/pelvis as well as
CT
Small sample size therefore limited power
15% more cancers in patients with a history of
exposure but difference was not statistically significant
Headline = “NO SIGNIFICANT RISK”
Carcinogenesis and Fetal
Radiation
• Carcinogenesis is believed to be a stochastic effect of radiation (i.e., no
threshold dose). The risk of childhood malignancy after in utero irradiation
was first reported in 1956 [1], though the association was not widely
accepted until the early 1960s
– Baseline risk of childhood cancer19/10,000
– Baseline risk of fatal childhood (0-15 yrs) cancer [2]5/10,000
– Excess risk of fatal childhood cancer per rad of fetal whole body dose
[3]4.6/10,000
– Excess risk of childhood cancer per rad of fetal whole body dose [4]6.4/10,000
– Excess risk of childhood cancer per rad of fetal whole body dose [5]:6/10,000
– Relative risk of childhood cancer after fetal radiation exposure of 5 rad [6]:2
• increased risk of childhood cancer of up to 2 times baseline for a standard
pelvic CT.
UCSF Department of Radiology Guidelines
Carcinogenesis and Fetal
Radiation
• The relationship between carcinogenesis and gestational age is
controversial [9]. The OSCC study suggests the risk is higher with exposure
in the first trimester than with exposure in the second or third trimesters, with
relative risks of 3.19, 1.29 and 1.30, respectively [10].
• Assuming a relatively high fetal dose estimate of 5 rads for a pelvic CT
during pregnancy, the relative risk of fatal childhood cancer may be doubled.
This relative risk may appear substantial, but it should be remembered that
the baseline risk is very low, so that the odds of dying of childhood cancer go
from 1 in 2000 (baseline) to 2 in 2000 (after 5 rads).
– risk comparisons driving 20,000 miles in a car
– living in New York City for 3 years
• Key point: CT of the fetus should be avoided in all trimesters of pregnancy,
because it may cause up to a doubling of the risk of fatal childhood cancer.
UCSF Department of Radiology Guidelines
MRI in Pregnancy
• Abdomino-pelvic MRI
– Highly accurate for appendicitis
• Reported 100 Sens and 94% Spec
• Start with U/S and still can do CT if needed
– Other findings: ureteral stone, cholecystitis,
infarcted fibroid… visible
• Discouraged in First Trimester
– Heating concerns
– Number one cause for MRI injury overall are
thermal injuries
Thermal Injury MRI
Summary
• Radiation Carcinogenesis is assumed to have no
lower limit of exposure below which is 100% safe
• Medical imaging has double the US annual
population exposure to radiation and CT is
primarily responsible
• Residential radon gas is number one non-imaging
cause for exposure
• Fetal exposure to radiation is likely most sensitive
period for carcinogenesis
Fetal Radiation References
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1.Stewart A, Webb J, Giles D, Hewitt D. Malignant disease in childhood and diagnostic irradiation in utero. Lancet 1956; 2: 447.
2.Roberts PJ, Given-Wilson R, Gifford D, Bryan G. Pregnancy and work in diagnostic imaging. Report of a joint working party of
the Royal College of Radiologists and British Institute of Radiology. British Institute of Radiology, London, 1992.
3.Mole RH. Childhood cancer after prenatal exposure to diagnostic x-ray examinations in Britain. Br J Cancer 1990; 62: 152168.
4.United Nations Scientific Committee on the Effects of Atomic Radiation. Ionizing radiation: levels and effects. 1972 Report to
the General Assembly, with annexes. Vol II. Effects. New York, United Nations, 1972.
5.Muirhead CR, Cox R, Stather JW, et al. Estimates of late radiation risks to the UK population. Documents of the NRPB 4 [4].
Chilton: National Radiological Protection Board, 1993: 15-157.
6.Ginsberg JS, Hirsh J, Rainbow AJ, Coates G. Risks to the fetus of radiologic procedures used in the diagnosis of maternal
venous thromboembolic disease. Thrombosis and Haemostasis 1989; 61: 189-196.
7.Damilakis J, Prassopoulos P, Perisinakis K, Faflia C, Gourtsoyiannis N. CT of the sacroiliac joints: Dosimetry and optimal
settings for a high-resolution technique. Acta Radiol 1997; 38: 870-875.
8.Damilakis J, Perisinakis K, Voloudaki A, Gourtsoyiannis N. Estimation of fetal radiation dose from computed tomography
scanning in late pregnancy: depth-dose data from routine examinations. Investigative Radiology 2000; 35: 527-533.
9.Doll R, Wakeford R. Risk of childhood cancer from fetal irradiation. Br J Radiol 1997; 70: 130-139.
10.Gilman EA, Kneale GW, Knox EG, Stewart AM. Pregnancy X-rays and childhood cancers: effects of exposure age and
radiation dose. J Radiol Prot 1988; 8: 3-8.
11.Benjamin SA, Lee AC, Angleton GM, et al. Neoplasms in young dogs after perinatal irradiation. J Natl Cancer Inst 1986; 77:
563-571.
12.http://www.physics.isu.edu/radinf/risk.htm. Accessed 3/14/06.
13.ACOG Committee on Obstetric Practice. ACOG Committee Opinion. Number 299, September 2004. Guidelines for
diagnostic imaging during pregnancy. Obstet Gynecol. 2004; 104: 647-651.
Reference Material
ACR Appropriateness Criteria
https://acsearch.acr.org/list
Acute Pancreatitis
RUQ pain
Flank Pain- recurrent Sx stone variant
Pyelonephritis
Crohn dz
Palpable abdominal mass
Right Lower Quadrant Pain- pregnant pt variant (adults rec CT and peds we already do US)
Rib fractures
Headache
Links for additional references
Beir VII report
http://www.nap.edu/catalog.php?record_id=11340
Image Wisely
http://www.imagewisely.org/
Xrayrisk.com