Studies say CT scans fuel surge in cancers

Researchers find extremely high levels of radiation

By: JournalNow Staff | LOS ANGELES TIMES
Published: December 16, 2009

Widespread overuse of CT scans and variations in radiation doses caused by different machines and different operators are subjecting patients to high doses of radiation that will lead to tens of thousands of new cancer cases and as many as 15,000 deaths for each year that the scanners are used, researchers reported yesterday.

Several recent studies have suggested that patients have been unnecessarily exposed to radiation from CTs or have received excessive amounts, but two studies reported yesterday in the Archives of Internal Medicine are the first to quantify the extent of exposure and the related risks.

In one study, researchers from the University of California, San Francisco found that the same imaging procedure performed at different institutions -- or even on different machines at the same hospital -- can yield a thirteenfold difference in radiation dose, potentially exposing some patients to inordinately high risk.

While a normal CT scan of the chest is the equivalent of about 100 chest X-rays, the team found that some scanners were giving the equivalent of 440 conventional X-rays. The absolute risk may be small for any single patient, but the sheer number of CT scans -- more than 70 million a year, 23 times the number in 1980 -- will produce a sharp increase in cancers and deaths, experts said.

"The articles in this issue make clear that there is far more radiation from medical CT scans than has been recognized previously," wrote Dr. Rita F. Redberg of UC San Francisco, the editor of the journal, in an editorial accompanying the reports.

Whole-body scans of healthy patients looking for hidden tumors or other illnesses are also becoming more common, even though they rarely find anything wrong. The irony is that, by exposing healthy people to radiation, they may be creating more problems than they solve.

CT scans, short for "computed tomography," provide exceptionally clear views of internal organs by combining data from multiple X-ray images. But the price for that clarity is increasing exposure to X-rays, which cause mutations in DNA that can lead to cancer.

Scanner manufacturers are designing new instruments that use lower doses of radiation, but many older machines rely on higher doses. Machine settings for particular procedures, furthermore, are not standardized, and individual radiologists use the technology differently in different patients, leading to variance in doses.