"The confirmation of low rates of referral to colonoscopy, the prevalence of advanced neoplasia and the prevalence of extracolonic findings makes CT colonography a viable option for Medicare-aged patients," first author Dr. Brooks D. Cash said in a statement.

Low dose

The average effective radiation dose was also rather moderate, according to the authors, at 4.24 millisieverts. To put that number in its proper context, the researchers said Americans receive about 6.2 mSv on average every year from background radiation. Doses under 50 mSv are not thought to be really medically significant, the researchers said, citing the Health Physics Society.

However, the study wasn't designed to address one CMS objection -- the unreliability of CTC in detecting polyps smaller than 6 millimeters, and whether that's a problem. Still, the researchers said their results provide "indirect evidence" of the rarity of neoplasia in polyps 5 millimeters or tinier.

"In the current study, none of the diminutive polyps identified and removed during colonoscopy harbored advanced neoplastic features, a reassuring observation in this group of older patients," the researchers wrote. "Conversely, advanced colorectal neoplasia was identified in almost 6 percent of patients with small (6-9 millimeter) polyps, supporting current recommendations for referral of these patients to colonoscopy for polypectomy."

The retrospective study was conducted between 2004 and 2009. The mean age for patients was 75. Most patients getting screened or scanned (58 percent) were men.

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