Proponents of virtual colonoscopies say they can save lives by screening people for colon cancer who might be reluctant to get an actual colonoscopy. But a new study suggests it had better increase the numbers of people getting screened by a significant amount if it's to be considered cost effective.

A report published Tuesday in the Journal of the National Cancer Institute found that the scans, known as computed tomographic colonographies, are less cost effective than regular colonoscopies unless they're reimbursed at a lower rate or they increase the number of people getting screened by at least 25 percent.

Some of these findings were shared with a Medicare advisory committee in Nov. 2008, lead researcher Amy B. Knudsen, a senior scientist with the Massachusetts General Hospital's Institute for Technology Assessment, told DOTmed News.

The results were among the body of research that convinced the Centers for Medicare and Medicaid Services not to reimburse the procedure, Knudsen said, though she said that CMS decided against paying for the scans largely because of concerns about extra-colonic findings and a dearth of studies on its effectiveness with a Medicare-aged population.

The CMS made its controversial decision, opposed by the American College of Radiology, in May 2009.

In the current study, using mathematical models based on patient data drawn from the Department of Defense and national CT colonography trials, the researchers estimate CTC scans cost $600,000 to $700,000 more than colonoscopies per 1,000 Medicare-aged patients 65 years old over the course of their lives.

The higher cumulative costs of the CTC scans came about because doctors must follow up abnormal findings on CTC scans with a colonoscopy anyway, Knudsen said.

As CTC scans aren't reimbursed by Medicare now, the researchers estimated their cost by looking at pelvic and abdominal CT scan rates, as well as the cost of processing and interpreting the images. According to their estimates, CTC scans cost about $488 each, just a smidgen less than a colonoscopy without polyp removal, at $498.

Screening with the CTC scans once every 5 years, as recommended by most radiologists, also resulted in fewer life-years gained, the researchers said: 143 to 178 years per 1,000 65-year-olds, compared with the 152-185 life-years per 1,000 65-year-olds gained from once-a-decade colonoscopies.

Nonetheless, CTC scans could be more cost effective if, as their advocates claim, they boosted the rate of people getting screened.

The researchers said if virtual colonoscopies convinced an additional 25 percent of otherwise unscreened people to get a scan, it would be cost-effective at the current rate of $488. If only 10 percent extra were encouraged, it would be cost-effective at $204 to $408, the authors said.

Currently, there's no evidence CTC scan availability increases screening compliance, Knudsen said.

In an accompanying editorial, Dr. Russell Harris, professor of medicine at UNC and a member of UNC Lineberger Comprehensive Cancer Center, said while the analysis was useful, the models might actually overestimate the cost-effectiveness of both screening tests. For instance, colonoscopy often results in harmless polyps being removed, which can result in excessive bleeding, and CTC scans can detect abnormalities outside the colon, such as in the kidneys or liver, which lead to further testing and surgery even though the treatment will not help the patients live longer.

Harris said, in the end, neither test is ideal.

"Wouldn't it be interesting if we ended up, a few years from now, with neither CTC nor colonoscopy as the primary screening test, but rather an improved fecal test as our gold standard?" Harris asked.