A new study published today in the Journal of the American Medical Association shows that radiation from a high-resolution cardiac CT scanthe newest, noninvasive test for detecting heart diseasemay slightly raise patients' lifetime risk of developing cancer. In general, the study found, the elevated risk of cancer was greatest for women and younger patients.
Led by Dr. Andrew Einstein, a cardiologist at the Columbia University College of Physicians and Surgeons, researchers calculated the lifetime attributable cancer risk associated with radiation exposure from a single scan (called computer tomography coronary angiography, or CTCA), based on the patient's sex and age. For example, the lifetime cancer risk following one CTCA was just 1 in 3,261 for an 80-year-old man; that risk jumped to 1 in 284 for a 40-year-old woman, and climbed higher still to 1 in 143 for a 20-year-old woman. At all ages for women, the risk of breast and lung cancers accounted for up to 85% of the total cancer risk from one scan. However, by using a radiation dose-reduction strategy during the CTCA, researchers were able to reduce overall cancer risks by 35%.
The question clinicians will need to consider is whether the benefits of CTCA outweigh the risks. In absolute terms, the lifelong attributable risk of cancer per CTCA scan was low, ranging from 0.02% (for an 80-year old man, with the dose-reduction strategy) to 1% (for a 20-year-old woman, with a regular heart and aorta scan). The benefits of CTCA are that it is noninvasive, quick (the test takes about 10 minutes), requires that the patient ingest less contrast dye than with other scans and can be performed immediately in an emergency room when someone is admitted with chest pain. According to the study's authors, emergency departments evaluate about 6 million patients each year for chest pain.
"This is the only technology available that will really define the presence or absence of calcified or non-calcified plaque," says Dr. Norman Lepor, a professor at UCLA's Geffen School of Medicine, referring to the tell-tale build-up on artery walls that signifies heart disease. Lepor says that CTCA gives off no more radiation than the routinely used diagnostic nuclear stress test, which also detects plaque deposits, but only those that are big enough to block 70% of the artery. "The risk-benefit assessment is in favor of cardiac CT to be used in a judicious fashion," says Lepor, who describes good candidates for the scan as male, over age 40 with at least one risk factor. But there's no need to image patients who don't have any risk factors. "This is not a test that should be done in any routine or repetitive fashion," says Lepor.
Einstein expects that the new study's findings will have several implications in the everyday practice of medicine. "I think this can reassure a lot of patients that CTCA is a good testand a safe test particularly for older patients," says Einstein. "On the other hand, for younger women, I think it may affect physicians' thinking in terms of the risk-benefit ratio of the test."
Because of the potential hazards involved with radiation exposure, Einstein warns patients against attempts to "get pretty pictures of their heart" without a doctor's recommendation. Otherwise, he says, the CTCA can be an excellent noninvasive alternative to the current gold standard test for heart disease, the coronary angiography, which involves threading a catheter from the groin to the heart's blood vessels, and can cause complications such as blood clots, infection and even death. CTCA is also a good substitute for the time-consuming diagnostic tests in use in emergency departments; with CTCA physicians can find out sooner when there is a problem with the patient's heart.
Down the line, Einstein believes his team's conclusions will boost cardiac diagnostic technology and prompt major manufacturers to improve it. "This is an impetus toward accelerating the pace of research in cardiac CT scans so as to reduce the dose to patients," says Einstein.
Lepor agrees. Though such technology is still in its early phases, he says, "Perhaps in five or seven years, we may have technologies using magnetic resonance that may allow us to see plaque without [radiation] exposure."