Having an X-ray to look for signs of colon cancer may soon be an option for those who dread the traditional scope exam.

Two of the largest studies yet of "virtual colonoscopy" show the experimental technique works just as well at spotting potentially cancerous growths as the more invasive method, according to a UW-Madison study being published in today's New England Journal of Medicine. It's also quicker and cheaper.

The X-rays can help sort out who really needs the full exam and removal of suspicious growths, called polyps. In one study, only 8 percent of patients had to have followup traditional colonoscopies, which are done under sedation and carry a small risk of puncturing the bowel.

But what some people consider the most unpleasant part can't be avoided: drinking laxatives to purge the bowel so growths can be seen.

Still, proponents hope that the newer test will lure those who have balked at getting conventional screening.

"This is ready for prime time," said Dr. Perry Pickhardt, one of the UW-Madison researchers reporting the results of the study.

A second, federally funded study at 15 sites around the country is meant to be the definitive test of virtual colonoscopy. Results have not been published, but they show the test to be promising.

Colonoscopies are recommended for everyone over 50, but just about half get tested. Colon cancer is the nation's second-leading cause of cancer deaths, and an estimated 52,000 people will die from it this year.

In traditional colonoscopy, performed by a gastroenterologist, a long, thin tube is inserted and snaked through the large intestines. Generally, any polyps that are spotted, regardless of size, are taken out in the process.

Virtual colonography uses a CT scanner to take a series of X-rays of the colon and a computer to create a 3-D view. A small tube is inserted in the rectum to inflate the colon so it can be more easily viewed. A radiologist then checks the images for suspicious polyps. Since the patient isn't sedated, there's no recovery time required.

But if any polyps need to be removed, the patient must then have a regular colonoscopy to do that.

For the Wisconsin study, Pickhardt persuaded health insurers in Madison to pay for the less expensive virtual colonoscopies and let patients choose between the two exams. The study included 3,120 patients who opted for a virtual colonoscopy and 3,163 who chose the traditional exam.

Most insurance companies don't cover virtual colonoscopy for screening but that could change if colon cancer screening guidelines endorse it.

Virtual screenings are already available at some hospitals and centers for people willing to pay for it.

The American Cancer Society is updating its guidelines, but Robert Smith, director of cancer screening, wouldn't say whether they would now recommend virtual colonoscopy, also known as CT colonography.

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