Exposure to low doses of radiation from heart scans is associated with a very small increase in cancer risk, a new study suggests.

Researchers found that there is a 3 percent increased risk of cancer for every 10 milliSieverts (mSv) of radiation. To put that amount of radiation in perspective, a chest X-ray gives 0.04 to 0.10 mSv of radiation, and a coronary angiogram (heart screen) delivers between 2.1 and 4 mSv of radiation, according to the 2008 Manual of Cardiovascular Medicine.

Exposure to radiation among patients in the study averaged 5.3 mSv per year, the study said.

However, the vast majority of cancers are not related to radiation from imaging. And in most cases, cancer risks are outweighed by the benefits of detecting complications after a heart attack, said study researcher Dr. Mark J. Eisenberg, a professor of medicine at McGill University in Canada.

"If a patient is having a heart attack, and it can be aborted by an emergency angiogram and angioplasty, the benefits far outweigh the tiny risk of developing a cancer in the future," Eisenberg told MyHealthNewsDaily.

The study was published Monday in the Canadian Medical Association Journal.

Analyzing the angiograms

Eisenberg and his colleagues looked at the medical data of 82,861 people who had a heart attack between April 1996 and March 2006. Seventy-seven percent of them had at least one procedure with low-dose ionizing radiation within one year of their heart attack, the study said.

Researchers followed up with the patients a year after they were admitted to the hospital, and found that 12,020 had developed cancer. They found that the more radiation the heart patients had been exposed to, the higher their risk of cancer.

People who had a cardiologist as their treating physician were exposed to more radiation than people who had a general practitioner as their treating physician. Most people received low or moderate doses of radiation, but young males tended to be exposed to higher doses of radiation than other people, the study said, though researchers did not know the exact reasons why.

The majority of the cancers these patients developed were in the abdomen, pelvis and chest region, according to the study.

More than a million people undergo angiography every year in the United States. The process involves injecting a dye into the arteries, and seeing how freely it moves via an X-ray, according to the National Institutes of Health.

Weighing the risks

The findings shouldn't make people afraid to get heart scans, especially because the scans can expose life-threatening complications, said Dr. U. Joseph Schoepf, director of cardiovascular imaging at Medical University of South Carolina, who wasn't involved with the study.

"There is an extremely small risk [of cancer], as opposed to the very real and practical risk of dying either from myocardial infarction itself if not treated appropriately, or if complications aren't caught in time," Schoepf told MyHealthNewsDaily.

But the study should prompt doctors to keep track of what imaging procedures their patients have previously undergone, because the radiation exposures can add up, Eisenberg said.

"Multiple doctors can be ordering multiple different imaging tests and procedures in patients in different hospitals, and no one is keeping track," Eisenberg said. "This was not a big problem in the past, but with the explosion in imaging procedures, we need to start thinking about instituting such a system."

Doctors should instead consider using stress tests, such as those done on treadmills, and echocardiography, which involves no radiation, to test for heart risks if their patients have already been exposed to a lot of radiation, he said.