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 (CAC) scanning with computed tomography (CT) in asymptomatic individuals remains an elusive goal. In this issue of the Archives, Kim et al1 contribute to our knowledge about potential risks by reporting estimated radiation doses and excess lifetime risks of radiation-induced cancer from CAC scanning for a variety of CT scanners and scanning protocols that have been described in the literature. The authors report more than a 10-fold variation in effective radiation dose, from 0.8 to 10.5 mSv, with a median of 2.3 mSv. The data reflect well-established relationships between the specifics of CT scanner settings such as x-ray tube potential or tube current-time product on the one hand and radiation exposure and dose on the other.2 For their median radiation dose, Kim and colleagues estimate a lifetime excess cancer risk from a single examination at the age of 40 years of 9 cancers per 100 000 men and 28 cancers per 100 000 women.
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