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Are virtual colon cancer screenings ready for real-world usage?

Almost. In fact, by the end of the year, the American Cancer Society, which is now working on new guidelines, may include virtual colonography as one of the recommended ways to screen Americans over 50 for colon cancer.

In a virtual colonography, the colon is examined by a CT scan -- a less invasive screening method than a conventional colonoscopy, in which patients often have to be sedated so a viewing tube can be inserted into the rectum.

So far, most insurers do not pay for a virtual colonography, which costs about $650. But data from a trial expected to be published later this year, as well as a study published in the journal Cancer late last month, are building momentum for greater acceptance.

With virtual colonography, if polyps larger than 5 millimeters are found, the patient must have a regular colonoscopy so that a doctor can snip the polyps out.

A growing body of evidence suggests that polyps smaller than 5 millimeters are not dangerous so long as you get a repeat scan in 10 years, said Dr. Michael Zalis , director of CT colonography at Massachusetts General Hospital. Since most polyps are this tiny, virtual colonography means that roughly 85 percent of the time, people need no further testing.

"Virtual colonoscopy is equal to conventional colonoscopy for detecting the polyps that matter -- those 6 millimeters or more. We don't even report the smaller polyps because the risk of invasive colonoscopy -- perforation and bleeding -- outweighs the minuscule cancer risk," said Dr. Perry Pickhardt, a radiologist at the University of Wisconsin.

Though some gastroenterologists have feared that if everybody switches to virtual exams, their incomes could go down, said Pickhardt , the lead author of the Cancer study, said this has not happened in his program. Because the virtual exam is less anxiety-provoking, more people actually get screened, he said. And there are enough people who do need further testing that gastroenterologists' business has actually increased, he said.

JUDY FOREMAN

E-mail health questions to foreman@globe.com.

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