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CT scans increasing lifetime cancer risk
Higher frequency of scans, variation in radiation doses may be endangering patients.
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The use of CT scans has increased dramatically in the last decade or more, and recently published research indicates that this may ultimately result in an increase in the number of radiation-related cancer cases – and cancer-related mortality.
Two studies, published in the Archives of Internal Medicine, attempted to quantify the effect of CT on cancer incidence and mortality.
“Every day, more than 19,500 CT scans are performed in the United States, subjecting each patient to the equivalent of 30 to 442 chest radiographs per scan,” Rita Redberg, MD, MSc, professor of medicine and director of Women’s Cardiovascular Services, division of cardiology, University of California, San Francisco Medical Center, wrote in an accompanying editorial “What is becoming clear … is that the large doses of radiation from such scans will translate, statistically, into additional cancers.”
Radiation doses
The first study, conducted by Rebecca Smith-Bindman, MD, of the University of California, San Francisco, and colleagues, was a retrospective cross-sectional study examining the radiation doses used with the 11 most common types of diagnostic CT scans. Data were examined for 1,119 consecutive adults in four centers in the San Francisco Bay area between January and May 2008.
Results identified a mean 13-fold variation between the highest radiation dose and the lowest for each CT study type. Although in some procedures radiation exposure was as low as 2 mSv, the dose increased to 31 mSv for a multiphase abdomen and pelvis CT scan.
“Even the median doses are four times higher than they are supposed to be, according to the currently quoted radiation dose for these tests,” Redberg wrote in her editorial. “Just one CT coronary angiogram, on average, delivers the equivalent of 309 chest radiographs. By their calculations, one in every 270 40-year-old women undergoing CT coronary angiogram will develop cancer from the procedure.” This is compared to one in every 8,100 women who had a routine head CT scan at the same age.
Radiation-related cancers
In the second study, Amy Berrington de González, PhD, an adjunct assistant professor at Johns Hopkins Bloomberg School of Public Health, and colleagues constructed a risk model to estimate age-specific cancer risk for each CT scan type. Data were derived from the National Research Council’s “Biological Effects of Ionizing Radiation” report, national surveys and insurance claims.
They found that approximately 29,000 future cases of cancer could be due to CT scans that took place in 2007. Abdomen, pelvis, chest, head and CT angiography were the largest contributors to the risk.
About 35% of these cancers were from CT scans in people when they were aged 35 to 54 years. Lung cancer was the most common radiation-related cancer, followed by colon cancer and leukemia.
“Presumably, as the number of CT scans increase from the 2007 rate, the number of excess cancers also will increase,” Redberg wrote. “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.”
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