Studies quantify radiation doses, cancer risks from CT scans

Doses of radiation from commonly performed computed tomography (CT) scans vary widely, appear higher than generally believed and may contribute to an estimated tens of thousands of future cancer cases, according to two reports in the December 14/28 issue of Archives of Internal Medicine, one of the JAMA/Archives journals.

CT scans have become increasingly common in the United States—about 70 million were performed in 2007, up from 3 million in 1980, according to background information in one of the articles. "While CT scans can provide great medical benefits, there is concern about potential future cancer risks because they involve much higher radiation doses than conventional diagnostic X-rays," the authors of one report write. For example, a chest CT scan exposes the patient to more than 100 times the radiation dose of a routine chest X-ray. "The risks to individuals are likely to be small, but because of the large number of persons exposed annually, even small risks could translate into a considerable number of future cancers."

It is important to understand how much radiation medical imaging delivers to help balance benefits and risks, the authors note. In one paper, Rebecca Smith-Bindman, M.D., of the University of California, San Francisco, and colleagues studied 1,119 patients undergoing the 11 most common types of diagnostic CT scans at four area institutions in 2008. Using hospital records, they calculated the radiation dosage involved with each scan and then estimated lifetime risks of cancer that could be attributed to those scans.

Radiation dosage varied widely between different types of CT studies; median (midpoint) doses ranged from 2 millisieverts for a routine head CT scan to 31 millisieverts for a multiphase abdomen and pelvis scan. "Within each type of CT study, effective dose varied significantly within and across institutions, with a mean [average] 13-fold variation between the highest and lowest dose for each study type," the authors write.

The estimated number of CT scans that would lead to the development of one cancer case also varied by type of CT scan and also by each patient's age and sex.

source: Eurekalert