New, Higher Cancer Risk Estimates for CR Scans

Moral of the story: CT scans are being reevaluated for their cancer risk, which was underestimated in the past based on theoretical values and not actual practice data.

Source: ACP Internist Weekly 12/21/09

New estimates on cancer risk of CT scans

Two new studies warn of the cancer risk posed by CT scans and suggest some risk-reduction strategies.
A retrospective cross-sectional study calculated the radiation doses delivered by computed tomography (CT) scans performed at four different California hospitals. Doses ranged from 2 millisieverts (mSv) for a routine head CT to 31 mSv for a multiphase abdomen and pelvis scan. Many of the scans provided more radiation than is usually assumed to be the case; the median dose for a routine abdomen and pelvis scan was 66% higher than the expected 8 to 10 mSv. Even within each type of study, the effective dose varied significantly within and among the hospitals. There was a mean 13-fold variation between the highest and lowest doses for each procedure.
Extrapolating from these data, researchers calculated cancer risks, such that 1 in 270 women who underwent CT coronary angiography at age 40 would develop cancer from the scan. Risks were lower for men than women, and higher for younger than older patients (20-year-olds faced double the risk, 60-year-olds only half). The study was published in the Dec. 14/28 Archives of Internal Medicine.
Another study in the same issue used risk models to calculate how many cancers could eventually be attributed to CTs based on current scanning rates. Overall, they estimated that 29,000 future cancers could be caused by CT scans performed in the U.S. in 2007. Scans of the abdomen and pelvis contributed the most to the tally, and one-third of the cancers would be due to scans performed on patients between the ages of 35 and 54.
The authors of the studies and an accompanying editorial offered a number of solutions to this problem, including standardized protocols (such as have been applied to mammography), fewer multiple series examinations, dose reduction and registration, and greater use of American College of Radiology accreditation and criteria. The experts also called for a reduction in the number of inappropriate and unnecessary CT scans.