Study estimates cancer risks for widespread calcium screening

Calcium artery calcium (CAC) screening might cause 42 and 62 excess cases of cancer per 100,000 men and women respectively, according to a new study in the Archives of Internal Medicine. The study by Kim and colleagues also found a more than 10-fold variation in radiation dose.

The investigators note that the potential impact of even small increases in risk could have significant public health implications. SHAPE, for instance, advocates CAC screening for about 50 million Americans.

The authors cite a study by Diamond and Kaul that “estimated that 1-time screening of 50 million individuals could, assuming perfect statin adherence in patients with high CAC, prevent 24 000 deaths and 96 000 nonfatal cardiovascular events, at a net cost of $17 billion, equivalent to $32 000 per life-year equivalent saved in comparison to a standard prevention strategy based on National Cholesterol Education Program guidelines.” Kim and colleagues add to this calculation: “our estimates suggest that the single screening could result in about 5600 individuals (range, 2700-37 000 individuals depending on CT protocol) developing a radiation-induced cancer in the future.”

George Diamond responded to CardioBrief, saying the authors “fail to note that unconditional statin treatment prevents even more events at little more cost (and no risk of cancer).”

An accompanying editorial by Raymond Gibbons and Thomas Gerber points out that there is “a long-standing controversy about the health risks of ionizing radiation at the doses used in medical imaging that reflects uncertainty as to whether the observed risk from the high radiation doses of atomic bomb explosions and nuclear accidents can be extrapolated to the much lower radiation dose from imaging.”

The real risk of CAC scanning will likely never be known: “Given the many confounding issues in estimating effective dose and in estimating the risk of cancer at a low radiation dose, it is possible that definite, indisputable answers will never be obtained for the radiation risk associated with CAC scanning.”

Gibbons and Gerber write that future cost-effectiveness analyses of CAC shouldaccount for potential cancer risk, and “consent forms for any future research protocols involving CAC scoring should reflect Kim and colleagues’ data. Local institutional review boards should incorporate appropriate lay language to inform potential research subjects about this potential risk.”

In addition,”responsible professional organizations should advocate for standardization of CAC imaging with CT. In the meantime, ‘every effort should be made to reduce patient dose while balancing image noise and quality sufficient for confident interpretation,’ as recommended by the AHA in a recent science advisory.”

Here is the Archives press release:

Study Estimates Radiation Dose, Cancer Risk from Coronary Artery Calcium Screening

CHICAGO – A study based on computer modeling of radiation risk suggests that widespread screening for the buildup of calcium in the arteries using computed tomography scans would lead to an estimated 42 additional radiation-induced cancer cases per 100,000 men and 62 cases per 100,000 women, according to a report in the July 13 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.

Coronary artery calcification is associated with coronary artery disease. “Computed tomography (CT) has been proposed as a tool for routine screening for coronary artery calcification in asymptomatic individuals as part of a comprehensive risk assessment,” the authors write as background information in the article. Evidence suggests that this type of screening may detect the presence of calcium in the arteries of individuals who would be at low risk when assessed by traditional risk factors. “However, the potential risks of screening, including the risk of radiation-induced cancer, have to be considered along with the potential benefits.”

Kwang Pyo Kim, Ph.D., then of the National Cancer Institute, Bethesda, Md., and now of Kyung Hee University, Gyeonggi-do, Republic of Korea, and colleagues estimated the radiation doses delivered to adult patients undergoing CT screening for coronary artery calcification from a range of available protocols in the literature (there is not yet one agreed-upon standard). “Radiation risk models, derived using data from Japanese atomic bomb survivors and medically exposed cohorts, were used to estimate the excess lifetime risk of radiation-induced cancer,” the authors write.

Because of differences in scanner models and techniques, radiation dose from a single scan varied more than 10-fold, the authors note. Organs or tissues estimated to receive measurable radiation doses included the breast, lung, thyroid, esophagus, bone surface and adrenal glands. “The wide dose variation also resulted in wide variation in estimated radiation-induced cancer risk,” they continue. “Assuming screening every five years from the age of 45 to 75 years for men and 55 to 75 years for women, the estimated excess lifetime cancer risk using the median dose of 2.3 millisieverts was 42 cases per 100,000 men (range, 14 to 200 cases) and 62 cases per 100,000 women (range, 21 to 300 cases).”

There are currently no estimates of the benefits of CT screening for coronary artery calcification, but when they become available, they could be compared with these estimates of radiation-induced cancer risk to design appropriate detection and prevention strategies. “Many technical factors influence radiation dose from coronary artery calcification measurement with multidetector CT,” the authors write. “Careful optimization of these factors may reduce radiation exposure without detriment to the clinical purpose of the screening examination. Further efforts by professional societies are necessary to standardize protocols in order to decrease unnecessary radiation exposure and to minimize cancer risk.”
(Arch Intern Med. 2009;169[13]:1188-1194. Available pre-embargo to the media at www.jamamedia.org.)

Editor’s Note: Co-author Dr. Einstein is supported in part by a National Institutes of Health K12 Institutional Career Development Award. Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures, funding and support, etc.

Editorial: Results Shed Light on Risks and Benefits

“The critical appraisal of any medical test or strategy requires careful assessment of its potential risks, benefits and costs,” write Raymond J. Gibbons, M.D., and Thomas C. Gerber, M.D., Ph.D., of Mayo Clinic, Rochester, Minn., in an accompanying editorial.

“Accurate definition of the risks, benefits and costs of the use of coronary artery calcium scanning with computed tomography in asymptomatic individuals remains an elusive goal,” they write. “In this issue of the Archives, Kim et al contribute to our knowledge about potential risks by reporting estimated radiation doses and excess lifetime risks of radiation-induced cancer from coronary artery calcium scanning for a variety of CT scanners and scanning protocols that have been described in the literature.”

“For patients in whom coronary artery calcium scoring is considered, health care providers should ideally discuss the potential risks and benefits of the procedure,” they conclude. “This discussion should include the small radiation (and potential cancer) risk described by Kim et al.”
(Arch Intern Med. 2009;169[13]:1185-1187.)

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