In a new study of nearly one million adults between the ages of 18 and 64, nearly 70 percent of participants underwent at least one medical imaging procedure between July 2005 and December 2007, resulting in an average effective dose of radiation nearly double the amount they would otherwise be exposed to from natural sources.
Nearly 20 percent of participants received at least moderate annual doses of radiation from diagnostic tests, and women and older individuals were at greater risk for radiation exposure, according to a report in the August 27 issue of the New England Journal of Medicine.
The study looked at imaging procedures involving radiation for diagnostic or treatment purposes; procedures in which radiation was specifically delivered for treatment, such as radiation for cancer, were excluded. Computed tomography (CT) scans and nuclear imaging accounted for three-fourths of radiation exposure, with nuclear stress tests to detect coronary heart disease, also known as myocardial perfusion imaging, cited as the procedure accounting for the largest single radiation exposure (22 percent of total effective dose in study participants).
In an accompanying Perspective article, "Elements of Danger – The Case of Medical Imaging," Michael S. Lauer, M.D., director of the Divisions of Prevention and Population Sciences and of Cardiovascular Diseases at the National Heart, Lung, and Blood Institute (NHLBI), calls for more research to demonstrate whether the use of cardiovascular imaging tests, such as myocardial perfusion imaging and CT scans, improves patient outcomes. He notes that "no large-scale, randomized trials have shown that imaging [in patients with stable or suspected heart disease] prolongs life, improves quality of life, prevents major clinical events [such as heart attacks], or reduces long-term medical costs." The NHLBI is part of the National Institutes of Health.
Studies are needed to determine whether the benefits of such imaging procedures to diagnosis and treat patients outweigh the potential risks of cumulative radiation exposure, according to Lauer. He calls on clinicians to "think and talk explicitly about the elements of danger in exposing our patients to radiation. This means taking a careful history to determine the cumulative dose of radiation a patient has already received and providing proper, personalized information to each patient about the risk" of developing cancer from cumulative exposure to radiation.
Radiation exposure is a known risk factor for cancer. Recent estimates suggest, for example, that as many as two percent of cancers could be attributed to radiation during CT scans. Although the radiation exposure from a single test is minimal, the frequency of the use of imaging tests that emit radiation continues to grow expansively, and often patients undergo repeated or multiple types of tests, thereby increasing their cumulative exposure to potentially cancer-causing radiation. Since 1992, the number of CT scans obtained has quadrupled. In addition, use of myocardial perfusion scans – which accounted for the single most frequent test and the highest radiation dose -- increased by more than six percent per year between 1993 and 2001.
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