Heart scan radiation linked to higher cancer risk: study
Published Monday, February 7, 2011 2:48PM EST
Heart attack survivors who undergo scans and nuclear medicine tests tend to have higher rates of cancer than those with less exposure, a new Canadian study suggests.
The researchers, from the McGill University Health Centre and the Jewish General Hospital in Montreal, note that the use of cardiac imaging tests has exploded in recent years in both Canada and the U.S.
And yet, they point out, little attention has been paid to the cumulative effect of the radiation used in those tests, or on how they might be affecting cancer rates.
So for this study, which appears in the Canadian Medical Association Journal, the researchers looked almost 83,000 patients who had a heart attack between 1996 and 2006, but who had no history of cancer.
About 77 per cent underwent at least one cardiac procedure using low-dose ionizing radiation within a year of the attack.
The tests included a heart imaging test called myocardial perfusion imaging, angiogram procedures called diagnostic cardiac catheterization and percutaneous coronary intervention, as well as a form of nuclear imaging called cardiac resting ventriculography All the tests involve exposing patients to low-dose ionizing radiation.
While most patients received only a low or moderate level of radiation, a substantial group were exposed to high levels through repeated tests -- and these patients tended to be younger, healthy men.
The study's lead author, Dr. Louise Pilote, a researcher in epidemiology, says her team found a distinct link between the cumulative exposure to low-dose ionizing radiation from cardiac imaging and the risk of cancer.
Over the course of the study, the researchers found 12,000 incidents of cancers, with two-thirds of the cancers affecting the abdomen/pelvis and chest areas.
They calculated that for every 10 "milliSieverts" of ionizing radiation, there was a 3.0 per cent increase in the risk of cancer, the study found. (A milliSievert is commonly used to measure the radiation dose in diagnostic medical procedures.)
Since the risk for cancer grows with age, the researchers accounted for that in their calculations.
"These results call into question whether our current enthusiasm for imaging and therapeutic procedures after acute myocardial infarction should be tempered," she and her co-authors conclude.
But Pilote also cautioned that patients who need to undergo scans after a heart attack shouldn't be dissuaded from undergoing the tests because of these findings.
"In cardiac patients who just sustained a myocardial infarction [heart attack], it's clear that the exposure to these radiation (procedures) is warranted," Pilote told The Canadian Press in an interview.
"And it probably way outweighs the risk of them ever developing a cancer."
The researchers say there needs to be a system of documenting cardiac imaging tests and other radiation-based procedures each patient undergoes to keep track of a patient's exposure to ionizing radiation.
In a related commentary, McMaster University cardiologist Mathew Mercuri and coauthors write that, although the radiation exposure of many tests is often low, they carry some risk.
They say the best solution could mean using procedures with lower or no radiation exposure, especially if there are multiple procedures involved.
And they too, called for programs to track radiation doses in patients, noting that if such programs already exist for health care workers and nuclear industry workers, they should exist for heart patients as well.