Limiting radiation exposure in coronary CT angiography: much can be achieved with little extra effort

Abstract

Radiation dose is of concern in coronary CT angiography: a very recent international survey of 50 sites which routinely perform coronary CT angiography— the PROTECTION I study—revealed that some centers performed their scans with average effective radiation doses as high as 30 mSv [1]. However, these high doses are only one end of what is really a spectrum—in fact, a quite extreme end of that spectrum. In PROTECTION I, some sites used average dose as low as 5 mSv, and the median effective dose associated with coronary CT angiography in a total of 1,965 patients was 12 mSv. This needs to be put in perspective in several respects. First of all, other diagnostic measures also expose patients to radiation. A recent Science Advisory of the American Heart Association reported typical effective doses of 7 mSv for an invasive coronary angiogram, 15 mSv for a percutaneous coronary intervention, 9 mSv for a sestamibi 1-day stress/rest myocardial perfusion scan and 41 mSv for a thallium stress/rest myocardial perfusion scan [2]. This in no way means that the radiation exposure of coronary CTA is negligible or irrelevant, but in 2006, it was estimated that cardiac CT accounted for 1.5% of the collective CT-related radiation dose in the US population while cardiac nuclear medicine studies, of which more than 10 million were performed, accounted for about 20% of the collective CT-related radiation dose. Second, the effect of a given radiation exposure is extremely difficult to determine and it also varies tremendously, depending on who the exposed patient is. The induced lifetime cancer risk is superbly difficult to quantify. Assumptions are that an effective dose of 10 mSv increases the lifetime risk of fatal cancer by 0.5 per 1,000 individuals—while the background lifetime risk of ‘‘naturally occurring’’ cancer is 212 per 1,000 individuals (for comparison, the lifetime risk of a fatal motor vehicle accident is 12 per 1,000 individuals) [2]. Radiation effects in young patients and women are more severe than in older individuals and in men, so that protection from overly high radiation doses are most important in young individuals. In older patients, using a higher radiation dose for coronary CT angiography may be completely justified if it helps to avoid invasive coronary angiographies with the associated risk of invasive arterial access, such as bleeding. Radiation effects decrease and non radiation-related risks increase in older patients [3, 4] so that the balance may be entirely different than in younger individuals. All the same, there is absolutely no doubt that radiation exposure carries a risk, as small and difficult to quantify as it may be, and that doses should always be ‘‘as low as reasonably achievable’’. Tremendous progress has recently been made to provide low-dose Editorial Comment on 9396 (DOI: 10.1007/s10554-008-9396-z).