Feb. 3 (Bloomberg) -- Heart scans on average expose patients to radiation equivalent to getting 600 chest X-rays at once, according to the first study to measure emissions from the procedures.

Doctors aren’t always aware of the doses and many don’t use the best methods for reducing the radiation, said Thomas Gerber, the Mayo Clinic researcher who did the study. The average exposure from computerized tomography, or CT, scans of the heart was 885 milligrays per centimeter, according to the study, published in tomorrow’s issue of the Journal of the American Medical Association. The authors of the study recommended that doctors limit the use of CT heart scans.

“If you have a patient with no chest pain and no shortness of breath, then a test that uses that level of radiation isn’t right,” said study author Gerber, a cardiologist at the Mayo Clinic branch in Jacksonville, Florida, in a telephone interview today. “If the patient feels great and hasn’t got much in the way of risk factors, and the doctors insist they have the test, it might be reasonable to question it.”

Exposure to radiation increases the chance of getting cancer, and the risk varies from patient to patient, said Andrew Einstein, the author of an editorial in the journal, in a telephone interview. In a 60-year-old woman with one exposure to CT scanning, the risk of cancer might be 1 in 700, while in younger patients, particularly females, it could be higher, Einstein said. Two tests would double the risk, he said.

The procedures have become more common as the installation of CT scanners for heart applications has tripled in the last two years, wrote Einstein, a cardiologist at the Columbia University College of Physicians and Surgeons in New York, in the editorial.

Scan Advantage

The scans help detect blockages in arteries that provide blood to the heart, without the risks or discomfort of standard procedures that insert tubes into arteries around the organ.

The additional lifetime risk of cancer from such scanning is “small,” the study authors wrote. For a CT abdominal scan, the additional lifetime risk of death from cancer is about 0.02 percent.

The international data were collected over a course of a month in 2007, at 50 sites in Argentina, Australia, Austria, Belgium, Brussels, Brazil, Canada, Denmark, Germany, Italy, Israel, Japan, Korea, Malaysia, Mexico, Monaco, the Netherlands, Pakistan, Portugal, Singapore, Spain, Switzerland, Turkey, the U.K. and the U.S. About 1,900 patients were evaluated.

The study was supported by Deutsches Herzzentrum Muenchen, Klinik an der Technischen Universitat; and by Bundesministerium fuer Bildung und Forschung.

Doses Varied

The doses of radiation from scans measured in the study were variable, Gerber said. Obese patients required more radiation, and the larger the area of the chest that needed to be scanned, the higher a dose was used, he said.

A dosing algorithm used to reduce radiation exposure by 25 percent was used almost three-quarters of the time. The algorithm should be widely adopted, wrote Columbia University’s Einstein, who wasn’t involved in the study.

A tactic called “sequential scanning” -- in which the CT scan of the heart is done in pieces, with the X-ray on for a brief part of each scan -- reduces the dose of radiation by 78 percent. It was used 6 percent of the time.

Coronary artery disease, the leading cause of death in the U.S., occurs when vessels that supply blood to the heart become narrowed or blocked by buildup of plaque on their walls, according to the National Institutes of Health. Symptoms include chest pain, and the condition can lead to heart attacks.

A previous study, published in the New England Journal of Medicine, said CT scans for finding heart disease weren’t as reliable as the standard method, catheterization, which involves threading a tube into the patient’s artery.

To contact the reporter on this story: Elizabeth Lopatto in New York at elopatto@bloomberg.net.

Last Updated: February 3, 2009 16:58 EST