In a standard colonoscopy, polyps can be removed during the scoping procedure itself, Fletcher pointed out.
In addition, there is a concern about the dose of potentially harmful radiation received by the patient from the X-ray, Fletcher noted. Multiple CT colonographies would mean multiple doses of this radiation, he said.
"Most important, from my point of view, are the extra-colonic findings with CT colonoscopy. Findings you never set out to find, but nevertheless once you see them you have to go on to further evaluate them, which involves cost and risk, " he said.
That's because -- unlike standard colonoscopy -- CT colonoscopy doesn't only depict the colon, but the whole abdomen. It will show cysts and other growths in the liver and kidneys that can lead to further testing in many patients. "Those tests may often be futile and in any case may be dangerous and certainly are costly," Fletcher said.
In terms of expense, standard colonoscopies can cost up to $3,000, while CT colonography has a price tag of between $300 to $800.
Another expert agreed with Fletcher that perhaps CMS had acted wisely.
"I am pleased with the decision," said Dr. Douglas Rex, director of endoscopy at Indiana University Hospital in Indianapolis. "The Medicare population is definitely not the right population to begin the CT colonoscopy experiment in. I was pleased that the people at CMS had the courage to make the right decision."
Rex said that older patients do have a much higher prevalence of polyps, "so many more patients, if they are screened initially with CT colonoscopy, are going to need a colonoscopy in order to remove polyps."
He also seconded Fletcher's concern that virtual colonoscopy would pick up too many innocuous aberrations outside the colon. "Most of these are incidental and not important to the patient but result in tests that increase the cost and the risk to patients," he said.
For more information on colon cancer, visit the American Cancer Society .
SOURCES: Abraham Dachman, M.D., American College of Radiology Colon Cancer Committee, and director of computed tomography, University of Chicago Medical Center; Robert Fletcher, M.D., professor of ambulatory care and prevention, Harvard Medical School, Boston; Douglas Rex, M.D., professor of medicine, Indiana University School of Medicine, director of endoscopy, Indiana University Hospital, Indianapolis; J. Leonard Lichtenfeld, M.D., deputy chief medical officer, American Cancer Society, official ACS blog