Radiation doses from CT scans may contribute to cancer risk, according to two reports published in Archives of Internal Medicine (2009;169[22]:2078-2086, 2071-2077).

According to background information provided in one of the studies, CT scans have become increasingly common in the US, with about 70 million being performed in 2007 alone.

“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 wrote. “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.”

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In a study of 1,119 patients undergoing the 11 most common types of diagnostic CT scans, Rebecca Smith-Bindman, MD, of the University of California, San Francisco, and colleagues calculated the radiation dosage involved with each scan and then estimated lifetime risks of cancer that could be attributed to those scans.

Dr Smith-Bindman’s study found that effective radiation dose varied significantly within and across institutions, with an average 13-fold variation between the highest and lowest does for each study type. In addition, the estimated number of CT scans that would lead to the development of one cancer case also varied by type of CT scan and by each patient’s age and sex, with an estimated 1 in 270 women and 1 in 600 men who undergo CT coronary angiography at 40 years old developing cancer as a result.

“The radiation exposure associated with CT has increased substantially over the past two decades, and efforts need to be undertaken to minimize radiation exposure from CT, including reducing unnecessary studies, reducing the dose per study and reducing the variation in dose across patients and facilities,” the authors concluded.

In a secondary study, led by Amy Berrington de Gonzalez, DPhil, of the National Cancer Institute, researchers sought out to estimate age-specific cancer risks for each scan type and reported that an estimated 29 000 future cancers could be related to CT scans. One-third of these projected cancer cases occurring following scans performed in individuals 35-54 years old, compared with 15% due to scans performed in children and teenagers.

“Changes made to practice now could help avoid the possibility of reaching the level of attributable risk of 2%. Our detailed estimates highlight several areas of use in which the public health impact may be largest, specifically abdomen and pelvis and chest CT scans in adults aged 35-54 years,” the authors concluded. “Further work is needed to investigate the balance of the risks and benefits from CT scan use and to assess the potential for dose or exposure reduction.”