Accuracy of virtual colonoscopies validated

Washington -- Virtual colonoscopies are poised to take off as a major screening tool for colorectal cancer -- the nation's second-leading cause of cancer death.

Findings from the American College of Radiology Imaging Network National CT Colonography Trial demonstrated that the noninvasive technique is as accurate as traditional colonoscopies at finding colorectal cancer and large precancerous polyps. Results from this large, multicenter study were published in the Sept. 18 New England Journal of Medicine.

The hope is that the wide adoption of virtual colonoscopies will encourage more people to be screened. Although screenings have increased in recent years to nearly 61% of those 50 and older, people still fall through the cracks, according to Centers for Disease Control and Prevention data.

In addition, a study published Sept. 8 in Cancer indicates that many colorectal cancer survivors do not receive recommended follow-up screenings.

The promise of CT colonography for screening has been building in recent years. In March, the American Cancer Society, the American College of Radiology and the U.S. Multi-Society Task Force added virtual colonoscopies to their list of recommended tests to detect cancer and polyps. The task force includes representatives of the American College of Gastroenterology, the American Gastroenterological Assn. and the American Society for Gastrointestinal Endoscopy.

"I think the clinical validation of the technique is complete," said C. Daniel Johnson, MD, lead investigator of the ACRIN trial and chair of the radiology department at Mayo Clinic's Scottsdale, Ariz., facility. In disclosures for the article, Dr. Johnson and other ACRIN investigators reported links to firms working on screening aids and techniques.

"Indeed, this study provides another push for noninvasive/minimally invasive screening by CT colonography," said David Kim, MD, assistant professor of abdominal imaging at the University of Wisconsin School of Medicine and Public Health. Dr. Kim, who was not involved in the ACRIN trial, was lead author of another study published last year in NEJM showing that colonoscopy and colonography had similar detection rates for large polyps. He reported serving on the advisory board for a laxative manufacturer and receiving lecture fees from a diagnostic software firm.

The ACRIN trial is the largest so far to compare the two technologies. It enrolled more than 2,600 men and women 50 and older at 15 sites across the country. The participants were scheduled for a standard screening colonoscopy and then agreed to have a virtual colonoscopy, or CT colonography, on the same day. The day before the exams, participants underwent colon-cleansing procedures prescribed by gastroenterologists.

The virtual and traditional screening results were compared, and researchers found that the virtual screenings identified 90% of the large polyps found by colonoscopies.

A cautionary note

In marking the study's findings, gastrointestinal specialists raised some cautions. "Colonoscopy is the only test that can both detect cancer at an early curable stage and prevent cancer by removing precancerous polyps," said a statement from the American Gastroenterological Assn.

The findings "underscore the reality that many patients who have polyps detected by CT colonography will still have to undergo complete colonoscopy," said American College of Gastroenterology President Amy Foxx-Orenstein, DO.

Plus, the virtual procedure also might cause some discomfort, she said, because it requires that the abdomen be insufflated with air or gas. Patients are not sedated for this procedure as they are for a colonoscopy.

"It is important for patients to understand that CT colonography does not at present represent a painless or risk-free procedure, nor does it eliminate the need for bowel cleaning, which patients report as a barrier to screening," she added.

The AGA statement also said CT colonography was less likely to detect small polyps measuring 5 mm to 9 mm. But it's not clear whether those smaller polyps pose a risk.

Additional obstacles must be overcome before virtual colonoscopy hits the mainstream. "The professional organizations need to review and adopt the evidence and insurance companies need to agree to cover it," Dr. Johnson said. To that end, "the Centers for Medicare and Medicaid Services are currently reviewing the technique for reimbursement."

"Once reimbursement has been established, it is anticipated that the use of [CT colonography] in screening will dramatically increase," Dr. Kim predicted.

Currently, only a few large-scale screening programs use colonography, he noted. Among them is a program at the University of Wisconsin where local HMO coverage for virtual screenings has been established. The Wisconsin program began in 2004 and has screened more than 5,000 people, he said. A few military hospitals also have established programs.