12.19.2009

Cat Scan Radiation Exposure and Cancer Risks

Several recent articles in he Archives of Internal Medicine outline the rapidly growing concerns about cancer risk and radiation exposure from CT scans. Each day there are over 19,500 Cat Scans performed in the U.S. With each scan the patient is exposed to the equivalent of 30 - 443 chest x-rays.

Smith-Bindman and colleagues3 collected actual data on radiation dosages for the most commonly used CT scans at 4 institutions in the San Francisco Bay area in California in 2008. They found a surprising variation in radiation dose—a mean 13-fold variation between the highest and lowest dose for each CT type studied (range, 6- to 22-fold difference across study types). The investigators found a median effective dose of 22 mSv from a typical Cat Scan coronary angiogram and 31 mSv for a multiphase abdomen-pelvis CT scan. At one institution, exposure was a staggering 90 mSv for a multiphase abdomen-pelvis CT scan.

Even the median doses are 4 times higher than they are supposed to be, according to the currently quoted radiation dose for these tests. Just 1 CT coronary angiogram, on average, delivers the equivalent of 309 chest radiographs. From their data, Smith-Bindman et al3 estimated the risk of cancer, taking into consideration age, sex, and study type. By their calculations, 1 in every 270 forty-year-old women undergoing a CT coronary angiogram will develop cancer from the procedure.

In a second study, Berrington de González and colleagues2 determined CT scan use frequency using data from a large commercial insurance database, Medicare claims data, and IMV Medical Information Division survey data. They estimated there were 72 million CT scans performed in 2007. Excluding scans conducted after a diagnosis of cancer and those performed in the last 5 years of life, Berrington de González et al2 projected 29 000 excess cancers as a result of the Cat Scans scans done in 2007. These cancers will appear in the next 20 to 30 years and by the authors' estimates, at a 50% mortality rate, will cause approximately 15 000 deaths annually.

In other words, 15 000 persons may die as a direct result of CT scans physicians had ordered in 2007 alone. Presumably, as the number of Cat Scans scans increase from the 2007 rate, the number of excess cancers also will increase. In light of these data, physicians (and their patients) cannot be complacent about the hazards of radiation or we risk creating a public health time bomb.