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.)

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

Relative Organ Risk and Age

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

• 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: 152-

168.

• 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