Virtual colonoscopy gets an endorsement

Virtual colonoscopy to screen for colorectal cancer has been in use in clinical trials for several years. Today, however, the technology was recommended for anyone who needs screening colonoscopy. While the test still requires what doctors politely call "bowel preparation," the new technology will be easier, safer and more comfortable for patients, to be sure.

The study endorsing widespread use of virtual colonoscopy is published in this week's New England Journal of Medicine. The largest study to estimate the accuracy of the technology, the research was sponsored by the National Cancer Institute and had 1,256 participants at 15 study sites, including UCLA. The participants underwent a virtual colonoscopy followed by a traditional colonoscopy, usually the same day. The results showed virtual colonoscopy is comparable in accuracy to traditional colonoscopy. Virtual colonoscopy was highly accurate in finding moderate to large polyps, which are unusual growths that could be cancerous or precancerous, and even very small polyps were detected with high sensitivity.

Colorectal cancer is the third most frequently diagnosed cancer in the country and the second leading cause of cancer death in American men and women. Colonoscopy is considered the definitive test for colorectal cancer screening and prevention.

"It is our hope that this less invasive option for screening will lead more people to get screened for colorectal cancer, which would result in fewer deaths," said Dr. Peter Zimmerman, principal investigator for the UCLA study site.

Virtual colonoscopy is performed with computerized tomography -- which is why it is also called CT colonoscopy. A standard colonoscopy uses a long, flexible tube with a camera that is threaded through the colon, but CT produces three-dimensional pictures taken with the CT scanner with only a thin tube inserted in the rectum. The test could greatly benefit the 5% to 10% of people who cannot have complete, regular colonoscopies because they have abdominal lesions or a very twisted colon.

There are some caveats to virtual colonoscopy, say experts from the American Gastroenterological Assn. For one, the test is more accurate in experienced hands. Also, if a polyp is found you still have to undergo a regular colonoscopy to have it removed. Finally, CT scans emit radiation. It's not easy to assess how much radiation people might get from virtual colonoscopy, however, because the exposure varies among the types of machines used, according to the AGA.

For more information on virtual colonoscopy, see the AGA web page entitled "What is CT colonography?"

An accompanying study, also in the New England Journal of Medicine, found that people need not have a colonoscopy any sooner than five years after the last normal scan. Many doctors recommend screening colonoscopy once every 10 years after age 50. But, until this new study, there were no data to support when another exam is warranted after the first normal one. People with symptoms, such as pain or bleeding, would need exams more often, as would anyone who has a family history of colon cancer.

-- Shari Roan

Photo: Computer-generated, 3-D picture taken from a CT colon exam. Credit: AP / Courtesy of Dr. Perry J. Pickhardt, University of Wisconsin Medical School.