People who undergo radiation-based tests and procedures after a heart attack may have a heightened risk of developing cancer down the road, a study published Monday suggests.
Researchers found that among nearly 83,000 Canadians who’d suffered a heart attack, the risk of developing cancer over five years inched up along with the patients’ exposure to radiation from heart procedures.
For every additional 10 millisieverts (mSv) in cumulative radiation dose received, the study found, the risk of developing cancer rose by 3 percent.
The common radiation-based procedures that heart attack patients undergo — including nuclear stress tests, heart catheterization and, increasingly, CT scans of the heart — typically deliver a radiation dose of between 5 and 15 mSv.
The study, published in the Canadian Medical Association Journal, is the latest to raise concerns about people’s increasing exposure to radiation from medical imaging. Growth in individuals’ potential lifetime radiation exposure has been driven largely by the growing use of CT scanning, which employs X-rays to produce three-dimensional images of the body, and nuclear medicine tests — wherein a small amount of radioactive material is injected into the bloodstream, concentrates in various tissues and is then read by special cameras.
However, the researchers stress that the cancer risk detected in the new study is small.
They say the findings should not scare heart disease patients away from needed procedures — certainly not from the potentially lifesaving catheterization procedures that might be done to treat a heart attack in progress.
During catheterization, a thin tube is threaded into the arteries leading to the heart and special X-ray images allow the doctor to locate any blockages; those blockages can then be cleared using a balloon-tipped catheter — a procedure known as angioplasty.
For someone having an acute heart attack, the benefits of those procedures “will greatly outweigh” any long-term cancer risk from radiation, said lead researcher Dr. Mark J. Eisenberg of McGill University and Jewish General Hospital in Montreal.
He noted that the bulk of patients’ radiation exposure in this study — 84 percent — came within a year of their heart attack. Catheterization and angioplasty accounted for most of that radiation, while nuclear scans accounted for about one-third.
“I think that the vast majority of those tests in the short term would be appropriate,” Eisenberg told Reuters Health.
Nonetheless, he said, the findings also suggest that doctors and hospitals should temper their enthusiasm for performing multiple radiation-based tests in people who’ve had heart attacks.
Eisenberg pointed out that some medical centers, particularly in the U.S., are aggressively marketing CT angiography, as a way to non-invasively peer into the heart arteries. Traditionally, one of these scans would deliver a radiation dose of around 16 mSv — though the newest scanners and techniques have trimmed the necessary radiation dose substantially.
Then there are nuclear stress tests. They are similar to traditional exercise stress tests, in which a person walks on a treadmill and has his or her heart activity monitored via electrodes placed on the body. But with the nuclear stress test, a radioactive substance is injected into the bloodstream, which allows the doctor to get a visual image of how well blood is feeding different parts of the heart muscle.
It’s not clear, though, that nuclear stress tests are any better than standard ones for evaluating people post-heart attack, Eisenberg said.
He suggested that when people with heart disease are advised to have a radiation-based procedure, they ask their doctor questions: Why is this test necessary? Are there any radiation-free alternatives?
He said they should also bring up any recent radiation-based tests they’ve had — like mammography breast cancer screening — so their cardiologist has an idea of their total radiation exposure.
“Work with your doctor to try to figure out what’s best for you,” agreed Mathew Mercuri, a researcher at Hamilton Health Sciences and McMaster University in Hamilton, Ontario.
But Mercuri, who co-wrote an editorial published with the study, also stressed that heart patients should not be alarmed by the findings.
During the study period, just over 12,000 of the 83,000 heart attack patients were diagnosed with cancer. But “only a few” of those cancers would likely be directly linked to their medical radiation exposure, according to Mercuri and his colleagues.
They estimate that for every 2,000 patients getting a 20-mSv dose of radiation, there would be one case of cancer attributable to the medical procedure.
“I don’t think individual patients should really be too worried by the findings,” Mercuri told Reuters Health.
He noted that the radiation dose from one heart procedure would be far less than that from a person’s lifetime exposure to the sun, for instance. (The average American is exposed to about 3 mSv of radiation per year from the sun and other natural sources, like radioactive substances in the ground and water.)
According to Mercuri, the findings are more important from the broader, public health standpoint. Since so many people are or will be undergoing radiation-based medical procedures, even a small cancer risk to an individual becomes substantial at the population level.
“As a healthcare community,” Mercuri said, “we need to make sure that people are getting the tests they need, and not getting the ones they don’t.”
He and Eisenberg both said that right now, there is no good way for doctors to know what a patients’ cumulative medical radiation exposure has been.
One idea being considered, Mercuri noted, is to create “smart cards” that would keep track of patients’ radiation doses from various medical procedures.
Source : Thomson Reuters