CT Scans Raise Cancer Risk

CT Scans Raise Cancer Risk

A new study just published in the April issue of the medical journal Radiology has a sobering conclusion for anyone who thinks “non-invasive” CT scans are simply pain-free, high tech medical marvels with no downside. The research shows that people who undergo numerous computed tomography (CT) scans over their lifetime may be at a significantly increased risk of cancer.

In fact, seven percent of the patients studied had enough recurrent CT testing to raise their estimated cancer risk by one percent or more above the baseline US cancer risk rate of 42 percent. Among the patients in the top percentile of cumulative lifetime attributable risk (LAR) of cancer, CT scans increased their chances of malignancies by 2.7 to 12 percent.

According to the Radiological Society of North America, some 68.7 million CT exams were performed in the U.S. in 2008 — that’s 6 million more than were performed in 2006. CT is commonly used to make medical diagnoses and to help figure out treatment options because the scanning technique provides detailed images of internal organs through digital imaging processing which generates a three-dimensional picture. To accomplish this, CT scanning involves taking a large series of two-dimensional X-ray images around a single axis of rotation. The result is that CT scans use higher radiation doses than most other imaging exams.

For their study, Aaron Sodickson, M.D., Ph.D., assistant director of Emergency Radiology at Brigham and Women’s Hospital and researcher at the Center for Evidence-Based Imaging in Boston, and his research team developed new methodology to estimate the cumulative radiation exposure for CT scans and the associated radiation-induced cancer risks for individual patients. The scientists took each patient’s CT history from electronic medical records and applied standard risk estimation models using a formula which takes into account the patient’s gender and age at time of x-ray exposure.

In all, some 31,462 adult patients were studied. All had diagnostic CT scans at Brigham and Women’s Hospital or the Dana-Farber Cancer Center in 2007 and had undergone a total of 190,712 CT exams over the previous 22 years. About 33 percent of the research subjects underwent five or more lifetime CT exams, five percent had more than 22 CT scans, and approximately one percent underwent more than 38 exams. Fifteen percent received estimated cumulative effective radiation doses of more than 100 millisieverts (mSv) — equal to the radiation from 1,000 chest x-rays. Four percent received a whopping radiation exposure of more than 250 mSv and one percent were subjected to over 399 mSv.

“CT is an excellent diagnostic tool of tremendous clinical value in many situations,” Dr. Sodickson said in a statement released to the media. “Individual decisions about its use should balance the expected clinical benefits against the potential cumulative risks of recurrent imaging.”

“However, we feel that a higher clinical threshold is warranted in patients undergoing a large amount of recurrent CT imaging, particularly if many of their prior CT scans have been negative. This scenario may result in a combination of high cumulative risk with low clinical benefit,” he added.

Dr. Sodickson also pointed out that the techniques implemented in his group’s study could be used to identify higher risk patients who might benefit from “enhanced radiation protection efforts”. This statement is of particular interest because it appears to indicate better radiation protection is available — although clearly not being routinely used.

Other scientists have previously urged restraint in using CT scans too often and have sounded alarms over the radiation exposure associated with the technology. For example, in 2007, writing in The New England Journal of Medicine, David J. Brenner, Ph.D., and Eric J. Hall, Ph.D., from the Center for Radiological Research at Columbia University Medical Center, argued that the potential cancer-causing effects from using CT scans might be underestimated or overlooked. In fact, they stated one third of all CT scans performed in the United States may not even be medically necessary.


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~ by sunil khemaney on April 6, 2009.

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