Feb. 3, 2009 -- Radiation doses from scans used to diagnose heart and vascular disease vary widely, and they could be reduced significantly if strategies for minimizing exposure were more widely followed, a new study shows.
Researchers estimated radiation exposures from cardiac computed tomography (CT) scans at 50 teaching and community hospitals throughout the world. Their study appears in the Feb. 4 issue of The Journal of the American Medical Association.
They found radiation exposures at the highest-dose sites to be six times as high as those at the lowest-dose sites.
And on average, the radiation exposure from a single, new-generation CT imaging test was equivalent to exposure from 600 conventional chest X-rays.
"That sounds really scary, but the chest X-ray isn't very useful for evaluating coronary artery disease so it really is a useless comparison," study researcher Jorg Hausleiter, MD, tells WebMD. "The more important point is that coronary CT is an excellent diagnostic tool for ruling out coronary artery disease. But we need to work to reduce radiation exposures."
64-Slice CT Scan
Since its introduction less than five years ago, the 64-slice CT scan had emerged as a leading tool for identifying clogged arteries and cardiovascular risk.
CT scanning in U.S. cardiology practices has increased threefold in the last two years and is expected to continue to rise.
But concerns about increases in cancer risk from increased radiation exposure remain.
"This new study highlights the fact that radiation doses from cardiac CT can still be quite high," Columbia University cardiologist Andrew J. Einstein, MD, PhD, tells WebMD. "That is of concern. But what we don't want is people avoiding these tests out of fear."
In a 2007 study, Einstein and colleagues concluded that the cancer risk from a single 64-slice CT heart scan was small but not negligible. The risk for women was found to be higher than for men and the risk to younger patients was higher than for older ones.
Mayo Clinic cardiologist Thomas C. Gerber, MD, PhD, who worked on the newly published study, tells WebMD that the cancer risk from diagnostic procedures like the 64-slice CT is not completely understood.
"We know the risk is low, but we don't know how low," he says.
Gerber emphasized that the wide variation of patient exposures in the study had little to do with technician error or carelessness.
And patient exposures at centers performing the most cardiac CT scans were not necessarily lower than exposure at centers performing fewer of the diagnostic tests.
One of the biggest dosage predictors was the use of strategies to lower radiation exposures to individual patients.
Only three-fourths of the centers participating in the study used a radiation-lowering strategy that has been shown to reduce exposure without affecting the efficacy of the scan. And other potentially more beneficial, but less well-studied, strategies have not been widely adopted.
Because the field is so new and it is so difficult to compare radiation doses of different centers, there is little that individual patients can do to minimize their exposure, short of avoiding redundant tests, Gerber says.
CT Scan Advisory
On Monday the American Heart Association issued an advisory to doctors in its journal Circulation, urging the judicious use of CT scans for the diagnosis of cardiovascular disease.
Gerber, who led the panel that wrote the advisory, says doctors need to carefully consider whether patients with chest pain or other symptoms consistent with heart disease will benefit from the test before ordering it.
The advisory also warns against using CT scans to screen asymptomatic patients who are at risk for cardiovascular disease.
"This is already happening, but there are no studies that show that screening asymptomatic patients and then changing their treatment based on the results impacts survival," he says.