Virtual Colonoscopy Nears Prime Time

CT Colon Scan Finds Cancer as Well as Colonoscopy

By Daniel J. DeNoon
WebMD Health News

Reviewed By Louise Chang, MD

Oct. 3, 2007 - Flying through your colon in virtual reality, Perry Pickhardt, MD, says he can find early colon cancer at least as well as a gastroenterologist using a very real colonoscope.

A new study backs up this boast by comparing colon cancer screening with virtual colonoscopy to screening with real colonoscopy. The study, in healthy, low-risk patients, compared the results of 3,120 consecutive virtual colonoscopies to results from 3,163 real colonoscopies.

"We found slightly more advanced polyps than colonoscopy did, and without any complications," Pickhardt tells WebMD. "The outcomes are not just good, but beyond our expectations. Nobody thought we would find more important things than did colonoscopy -- the current gold standard -- but we have."

Pickhardt, associate professor of radiology at the University of Wisconsin, is a pioneer in the field of virtual colonoscopy. Virtual colonoscopy, more accurately known as CT colonography or CTC, uses special software to view CT scans of a patient's colon. Experts using the technique can see colon polyps before they become deadly colon cancers.

"The reason we are able to find polyps so successfully is we find them on this 3-D reality fly-through," Pickhardt tells WebMD.

Doctors now agree that the best way to find colon polyps is with a colonoscope. But Pickhardt says that's going to change.

"Years from now we will be amazed we did such an invasive test for screening," he says.

Virtual Colonoscopy vs. Real Colonoscopy

The study by Pickhardt, David H. Kim, MD, and colleagues is not a randomized clinical trial. Instead of being randomly assigned to virtual colonoscopy or real colonoscopy, patients chose the screening method they wanted.

But both groups of patients were referred by the same doctors. Most patients in each group had no symptoms of colon cancer and were only at average risk.

The two techniques detected colon cancer at nearly the same rate. They also detected polyps larger than 10 millimeters -- a size considered dangerous -- at the same rate. Colonoscopy found far more tiny polyps than did CTC. But such polyps only very rarely carry cancer cells.

Colonoscopy has one big advantage: Any polyps that are found are immediately removed. Patients who have suspicious polyps found by CTC must undergo colonoscopy to have them removed. This happened to 8% of the patients in the study. Some patients with smaller polyps, however, chose to undergo CTC surveillance to see whether the polyps really were growing into something dangerous.

Seven of the patients who underwent colonoscopy screening had a colon puncture. This happens in about one in 500 colonoscopies and often requires surgical repair. The puncture rate seen in the study was in the expected range. There were no punctures in the CTC group.

Virtual Colonoscopy: Ready for Prime Time?

If CTC works so well, with so little risk, why isn't it now recommended for colon cancer screening? That's what WebMD asked Durado Brooks, MD, MPH, director of prostate and colorectal cancers for the American Cancer Society.

"The big question is whether the larger community of radiologists can get the same sort of very encouraging results we see in this study," Brooks tells WebMD. "These guys at Wisconsin have a great deal of experience using this technology in a setting where the technicians and everybody else is used to doing this. This is off the scale for community doctors who do CT scans."

But Brooks says we'll soon have an answer to this question. A large NCI-funded study is looking at how well CTC works when done by a large number of different radiologists. The study is completed and results should be available early next year.

"If these kinds of findings can be replicated, it would enhance the likelihood this would become another alternative for colorectal cancer screening," Brooks says. "So CT colonography could be added to the American Cancer Society recommendations if research suggests it can be done efficiently, safely, and with consistent performance in a variety of settings."

Pickhardt says an early look at the results of this CTC validation study are "very good" and "gratifying."

"If the American Cancer Society recognizes this as a valid colon cancer screening test, then insurance companies will pay for it and it will take off," he says. "This has been a long time coming, but now is an exciting time."

Kim, Pickhardt, and colleagues report their findings in the Oct. 4 issue of TheNew England Journal of Medicine.

SOURCES: Kim, D.H. New England Journal of Medicine, Oct. 4, 2007; vol: 357 pp. 1403-1412. Perry Pickhardt, MD, associate professor of radiology, University of Wisconsin Medical School, Madison. Durado Brooks, MD, MPH, director, prostate and colorectal cancers, American Cancer Society, Atlanta. Gatto, N.M. Journal of the National Cancer Institute, Feb. 5, 2003; vol: 95 pp: 230-236.

© 2007 WebMD Inc. All rights reserved.



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