The study found roughly a 14-fold difference in radiation dosage among the various CAC scan protocols. Eliminate two or three "outlying" readings, and the difference is still threefold, Einstein said.
But those estimates are suspect, said Dr. Thomas G. Gerber, an associate professor of medicine and radiology at the Mayo Clinic, and co-author of an accompanying editorial, because it is based on extrapolation of the damage done to people exposed to high doses of atomic bomb radiation at Hiroshima and Nagasaki.
"At the very low doses used in medical imaging, there is a huge controversy about whether there is an increased risk of anything," Gerber said. "Estimates of increased risk are based on a linear no-threshold hypothesis. There is even a theory that chronic exposure to low doses of radiation might be beneficial."
There is equal cloudiness on the benefit side of the equation, said Gerber. "I am not a strong proponent of screening," he added.
"The risk of cardiac events increases if calcium is present in the arteries," Gerber said. "But you can't pick up blockages before they are 70 percent or more. There is some debate about whether the risk predicted by coronary calcium screening is incremental [adds to] the risk predicted by conventional risk factors. It stands to reason that it might be, but that is not proven."
The U.S. Preventive Services Task Force recommends against using CT scans in screening programs, and the American Heart Association says they should be used for "selected individuals" at intermediate risk.
So what do physicians do about CAC scanning in the real world?
"I like using it for patients at intermediate risk of coronary disease, when I do not know how aggr
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