Virtual colonoscopies are excellent at detecting large and medium-sized polyps that can lead to colon cancer, according to the most definitive study yet published on this controversial technology.

In fact, these noninvasive tests are as effective as old-fashioned colonoscopies and ready to be widely used for cancer screening, said Dr. C. Daniel Johnson, lead author of the report published in the New England Journal of Medicine.

If more people get screened because they find the virtual alternative more acceptable, that could end up saving lives, he noted. More than half of Americans who should get colon cancer screenings don’t.

Insurance companies haven’t been willing to pay for virtual colonoscopies, citing insufficient evidence that they work. But that could change. Medicare is reviewing data from the new study, with an eye toward re-evaluating reimbursement.

¢ Colon cancer: This cancer is the second leading cause of cancer deaths in the U.S. and the third most common type of cancer. Screening for polyps is recommended at age 50, but traditional colonoscopies are so unpleasant that many people avoid them. They involve inserting a long tube topped with a miniature camera into the large intestine while the patient is under general anesthesia.

¢ The study: It was the largest of its kind to date, involving 2,600 men and women tested at 15 medical centers. All participants received both a virtual and a standard colonoscopy, with 99 percent of the duplicate procedures done on the same day. The virtual tests identified 90 percent of large polyps or cancers (1 centimeter or over) detected through the traditional colonoscopies. The study confirms earlier results on a larger scale, said Dr. Abraham Dachman, professor of radiology at the University of Chicago Medical Center and a co-author of the report.

¢ The procedure: Virtual colonoscopies involve a CT scan of the lower body. They don’t require anesthesia and are less invasive than the traditional procedures, which result in bowel perforations in 1 out of 1,000 patients.

Virtual colonoscopies are also less expensive because they’re done on an outpatient basis without an anesthesiologist and pathologist present. It’s common for standard colonoscopies to cost two to three times more than virtual procedures.

Patients still must take much-dreaded preparations that clean out their bowels, just as they do for traditional colonoscopies. If worrisome polyps show up, a patient will need a traditional colonoscopy so a physician can go in and remove them. About 4 percent of all patients who are screened will have polyps 1 centimeter or larger, and these clearly need to be excised, Johnson said. About 12 percent of patients will have polyps 6 centimeters or larger.

¢ Caveats: Smaller polyps are missed more often in virtual colonoscopies, said Dr. John Affronti, a professor at Loyola University Medical Center. Flat polyps also appear harder to detect.

In addition, even though radiation doses are half those of normal CT scans, “we still have to be concerned about the potential cumulative effects of radiation exposure,” said Dr. David Lichtenstein, director of endoscopy at Boston Medical Center. And often, the scans reveal abnormalities in other parts of the abdomen, which could lead to additional, unnecessary tests.

For Lichtenstein, the bottom line is “traditional colonoscopies remain the gold standard, but virtual colonoscopies are a good alternative” for people at average risk who can’t tolerate the prospect of having a tube inserted. People at high risk because of a family history or cancer, genetic mutations, or previous polyps should opt for the traditional approach, he and other experts say.