AIM: CT calcium screening poses increased cancer risk

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Widespread screening for the buildup of calcium in the arteries using CT scans could lead to an estimated 42 additional radiation-induced cancer cases per 100,000 men and 62 cases per 100,000 women, according to a computer modeling-based study in the July 13 issue of Archives of Internal Medicine.

Kwang Pyo Kim, PhD, then of the National Cancer Institute (NCI) in Bethesda, Md., and now of Kyung Hee University in Gyeonggi-do, South Korea, and colleagues estimated the radiation dose delivered to adult patients undergoing CT screening for coronary artery calcification from a range of available protocols in the literature.

"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 wrote.

Because of differences in scanner models and techniques, radiation dose from a single scan varied more than 10-fold, the researchers said. 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 continued. "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 mSv was 42 cases per 100,000 men (range, 14 to 200 cases) and 62 cases per 100,000 women (range, 21 to 300 cases)."

The investigators noted that 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 wrote. "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."

In an accompanying editorial, Raymond J. Gibbons, MD, and Thomas C. Gerber, MD, PhD, of Mayo Clinic in Rochester, Minn., wrote that the "critical appraisal of any medical test or strategy requires careful assessment of its potential risks, benefits and costs.

"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," Gibbons and Gerber wrote. "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, healthcare providers should ideally discuss the potential risks and benefits of the procedure," they concluded. "This discussion should include the small radiation (and potential cancer) risk described by Kim et al."