High radiation from CT scans raises concern about future cancers

Kathleen Blanchard's picture
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High radiation from CT scans, a widely used diagnostic tool, has raised concern among researchers about future cases of cancer. Radiation exposure to patients from CT scans varies, and may be higher than previously known.

Compared to conventional X-Rays, CT scans deliver higher doses of radiation. The authors of a new study, published in the Archives of Iinternal Medicine, say it is important to weigh the risks and benefits of radiation from CT scans. For instance, a CT scan of the chest delivers 100 times more radiation than a chest x-ray. The authors of this study say, "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."

In one paper, Rebecca Smith-Bindman, M.D., of the University of California, San Francisco and colleagues studied 1,119 patients in 2008 undergoing common CT scans. After calculating the radiation dose from each scan, the researchers then calculated individual lifetime risk of cancer.

They found that radiation doses from CT scans varied significantly, depending on the area of the body being scanned. Four institutions were studied, and the researchers also found differences in radiation doses, depending on where the CT scan was performed – a mean a variation of 13 fold was found between the highest and the lowest radiation dose delivered to patients during a CT scan.

There were also other variables found in the study between men and women that are also age dependent. For example, one in 600 men who undergo CT scan of the heart (coronary angiography) at age 40 will develop cancer as a result. One in 270 women would develop cancer. A routine CT scan of the head would lead to one cancer case among every 8,100 women and 11,080 men. “For 20-year-old patients, the risks were approximately doubled, and for 60-year-old patients, they were approximately 50 percent lower," the authors write.

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The study authors say radiation doses from CT scans have steadily increased over the last two decades. To minimize the risk of cancer from CT scans the authors say dosing should be standardized across institutions, the number of unnecessary CT scans should be reduced, and patient studies should be performed to determine the benefits of CT scans to patients versus risk of cancer from radiation.

An estimate from Amy Berrington de González, D. Phil., of the National Cancer Institute, Bethesda, Md and colleagues revealed that 29,000 future cases of cancer could be the result of CT scans performed in 2007. Two thirds of those cancers would occur in women, one third would occur among individuals age 35 to 54 from CT scans, and fifteen percent would occur among children and teens.

In an accompanying editorial Rita F. Redberg, M.D., M.Sc., of the University of California, San Francisco, and editor of Archives of Internal Medicine writes, "To avoid unnecessarily increasing cancer incidence in future years, every clinician must carefully assess the expected benefits of each CT scan and fully inform his or her patients of the known risks of radiation.”

The authors say more studies are needed to determine the risks and diagnostic benefits of CT scans and the impact on future cases of cancer.

The study highlights the risks of future cancer from a CT scans, especially for individuals age 35 to 54. The largest impact is associated with CT scans of the abdomen, pelvis and chest. Radiation from CT scans could be responsible for tens of thousands of future cases of cancer annually.

Arch Intern Med. 2009;169[22]:2049-2050

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