CT scans more harmful than thought

February 27, 2012

Cancer, Health Concerns

CT scans are performed in the U.S. more than 70 million times each year.

Several recent studies have suggested that patients receive excessive radiation from medical CT (computed tomography) scans, but two new studies published in December’s Archives of Internal Medicine are the first to quantify the extent of exposure and the related risks.

CT scans provide exceptionally clear views of internal organs by combining data from multiple X-ray images. University of California-San Francisco professor Rebecca Smith-Bindman, who led one study, said, “The risk associated with obtaining a CT is routinely quoted as ‘around one in 1,000 patients who undergo CT will get cancer.’ In our study, the risk of getting cancer in certain groups of patients for certain kinds of scans was as high as one in 80.”

Researchers from UC San Francisco found that the same imaging procedure performed at different institutions — or even on different machines at the same hospital — can yield a 13-fold difference in radiation dose, potentially exposing some patients to an inordinately high risk. Machine settings for particular procedures are not standardized, and individual radiologists use the technology differently for different patients, leading to a wide variance in doses.

While a normal CT scan of the chest is the equivalent of about 100 chest X-rays, the team found that some scanners were emitting the equivalent of 440 conventional X-rays.

In another study, epidemiologist Amy Berrington de Gonzales and her colleagues at the National Cancer Institute constructed a computer program to estimate the risks associated with CT scans. They concluded that about 29,000 future cancers could be related to CT scans performed in the United States in 2007 alone. That includes 14,000 cases resulting from scans of the abdomen and pelvis, 4,100 from chest scans and 2,700 from heart scans.

Taking into account the cancer mortality rate from radiation exposure, plus the age of the population undergoing such scans, the researchers estimated that the cases would result in as many as 14,500 deaths per year. Two-thirds of the cancers would be in women, who are more vulnerable to radiation. However, the conclusions were based on the assumption that the patients received a normal dose of radiation, but as the other studies showed, amounts of radiation vary widely.

The highest doses of radiation are routinely used for coronary angiography, in which cardiologists image the heart and its major blood vessels to look for blockages or other abnormalities. Under the normal dosages of radiation for the procedure, about 1 in 270 women and 1 in 600 men who receive it at age 40 will develop cancer as a result, reported Smith-Bindman.

CT scans are performed in the U.S. more than 70 million times each year. According to Dr. Michael S. Lauer of the National Heart, Lung and Blood Institute, there are no clinical trials showing that imaging saves lives.


Sources: USA Today December 14, 2009, MSNBC December 14, 2009 and

Reprinted from AzNetNews, Volume 29, Number 1, Feb/Mar 2010.

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