Taking into account the cancer mortality rate from radiation exposure, plus the age of the population undergoing such scans, the researchers estimated that the cases would result in 14,500 deaths per year.
Two-thirds of the cancers would be in women, who are more vulnerable to radiation. And the younger a patient is at the time of the scan, the higher the risk of cancer eventually developing.
Researchers' conclusions are based on the assumption that the patients receive a normal dose of radiation, but that is not necessarily a good assumption. Smith-Bindman and her colleagues studied the radiation doses received by 1,119 adult patients at four San Francisco Bay Area hospitals between Jan. 1 and May 30 of 2008.
Estimating the amount of radiation received by the patients, they concluded that dosing was highly variable both between institutions and within them as well. Some patients got below-normal doses.
There is little that individual patients can do about the vagaries of doses delivered by different machines.
But they do need to be their own advocates, said Dr. Rosaleen Parsons, chair of the department of diagnostic imaging at Fox Chase Cancer Center in Philadelphia.
Patients should keep their own records of the number of scans they have received, question why repeat studies are necessary and argue for other types of imaging, such as magnetic resonance imaging, or MRI, to minimize exposure to radiation, she said.