Cardiologists over the past five years have increasingly come to rely on a technology called cardiac computed tomography angiography (CCTA) to locate artery blockages in the heart. The downside: the procedure exposes patients to potentially cancer-causing radiation. How much radiation? According to a new study, exposure varies from hospital to hospital but the average dose of a single scan is equivalent to about 600 traditional chest x-rays.

Study co-author Thomas Gerber, a cardiologist at the Mayo Clinic in Jacksonville, Fla., says the advantage of CCTA scans is that they provide doctors with a direct view of the heart arteries, revealing tiny blockages that might be missed during traditional stress tests (which entail monitoring the heart rate, breathing, blood pressure and heart rhythm of a patient running on a treadmill). The major worry with such scans, he notes, is that they create images with the help of x-rays, which may increase the risk of developing cancer.

Gerber and his colleagues, from February to December 2007, studied the radiation exposure of 1,965 patients who received CCTA scans in 50 hospitals in the U.S., Europe, South America, and Asia. They asked doctors performing the procedure to record, among other things, how long each scan lasted and the strength of the electrical current used.

Based on this data, the researchers calculated each patient's "effective radiation dose," a value that takes into account the amount of radiation and the vulnerability of body parts exposed to it, such as the lungs and breasts. There was wide variation among hospitals ranging from five to 30 millisieverts (mSv); the average effective radiation dose was 12 mSv, which is about the same dose of 600 chest x-rays, according to the study.

"The risk of [these levels of] radiation in terms of causing cancer isn't understood very well," Gerber says, "but we can't completely dismiss the risk." 

David Brenner
, a radiation biophysicist at Columbia University Medical Center, says that a typical CCTA scan may increase the risk of developing cancer by as much as 0.04 percent for patients age 35 or older. The cancer risk associated with radiation exposure is much higher for younger people—10 times higher for an infant, for example—but that demographic is less likely to develop heart disease, according to the American Heart Association, and thus less likely to require CCTA scans.

Andrew Einstein, a cardiologist from Columbia University in New York City who wrote an editorial accompanying the study (and who has served as a consultant for companies that make CCTA machines), hopes the findings, published this week in the Journal of the American Medical Association, will encourage hospitals to use the smallest possible doses of radiation when giving CCTA scans. He notes, for example, that less radiation is needed on thin patients, because there's less tissue absorbing x-rays. Hospitals with older scanners might also consider upgrading to some of the newer lower radiation "sequential scanners" that deliver x-rays in pulses rather than a continuous beam, Einstein adds.

"It is important," Gerber says, "for doctors to get a sense [of] what the potential risks are."

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