Thousands of New Cancers Predicted Due to Increased Use of CT

From Medscape Medical News

Roxanne Nelson

December 17, 2009 — Computed tomography (CT) scans are widely used and are an invaluable tool for medical imaging. However, the possible overuse of CT scans and the variability in radiation doses might subsequently lead to thousands of cases of cancer, according to findings from 2 new studies published in the December 14/28 issue of the Archives of Internal Medicine.

In the first study, researchers found that radiation doses from common CT procedures are higher and more variable than what is typically cited. For example, the authors note that the median effective dose of an abdomen and pelvis CT scan is often cited as 8 to 10 mSv, but they found that the median dose of this type of scan was actually 66% higher, and the median dose of a multiphase CT scan of the abdomen and pelvis was nearly 4 times higher.

The authors also found a considerable range in doses within and across the institutions included in their study, with a mean 13-fold variation between the highest and lowest dose for each CT type studied.

In the second study, researchers estimated future cancer risks from current CT scan use in the United States, and projected that 29,000 future cancers will be directly attributable to CT scans that were performed in 2007. It is expected that the majority of these projected cancers will be caused by scans of the abdomen and pelvis (n = 14,000), chest (n = 4100), and head (n = 4000), and by CT coronary angiography (n = 2700).

What is becoming clear . . . is that the large doses of radiation from such scans will translate, statistically, into additional cancers.
More than 19,500 CT scans are performed every day in the United States; these expose each patient to the equivalent of 30 to 442 chest radiographs per scan, notes Rita F. Redberg, MD, MSc, professor of medicine at the University of California, San Francisco School of Medicine and editor of the Archives of Internal Medicine, in an accompanying editorial.

However, there is a question of benefit — whether these scans will lead to "demonstrable benefits through improvements in longevity or quality of life are hotly debated," she writes. "What is becoming clear, however, is that the large doses of radiation from such scans will translate, statistically, into additional cancers."

"We need to do something now, not wait 10 or 20 years to see the effects. It's not like radiation exposure can be undone after we find out that it does cause cancer," Dr. Redberg told Medscape Oncology.