A long-awaited federal study of an X-ray alternative to the dreaded colonoscopy confirmed its effectiveness at spotting most cancers, according to Thursday's New England Journal of Medicine.

The study focused on CT colonography, the so-called "virtual colonoscopy." It's a super X-ray of the colon that is quicker, cheaper and easier on the patient than traditional colonoscopies. Colonoscopies cost up to 3,000 dollars while the X-ray test costs 300 to 800.

In the study, both the standard colonoscopy and the X-ray test were given to 2,531 people at 15 U.S. medical centers. The largest of its kind, also known as virtual colonoscopy, identified nine out of 10 people who had cancers and large growths seen by regular colonoscopies.

The X-ray test's real value may be in showing who really needs a regular colonoscopy -- it was better at ruling cancer out than it was at detecting it.

The scans showed large growths in about one in six people, although some were false alarms not confirmed by colonoscopy.

But there were flaws, too. Among them: the radiologists sometimes misread the X-ray, leading them to spot polyps that weren't there, leading led to unnecessary follow-up testing.

The gold standard is colonoscopy, in which a long, thin tube equipped with a small video camera is snaked through the large intestine to view the lining. Any growth can be removed during the procedure.

It involves sedation and a missed day of work, not to mention preparation that uses pills or liquids to clean out the bowel.

Of the patients with growths verified by colonoscopy, 90 percent were flagged through the X-ray scans.

Virtual colonoscopies, currently recommended every five years, expose people to repeated doses of radiation. It's half the dose of a standard CT exam, but the cumulative effects are not yet known.

Colonoscopy is only recommended every 10 years, said Dr. C. Daniel Johnson, the lead author of the study and a researcher at the Mayo Clinic campus in Scottsdale, Ariz.

Back to the false alarms -- only one in four of those patients diagnosed with a growth actually had one, noted Dr. Robert Fletcher, a retired Harvard Medical School professor who wrote an editorial accompanying the study.

(Xinhua News Agency September 18, 2008)