CT Colonography: Ready for Prime Time

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On June 18, 2008, a letter was sent to the CMS Coverage and Analysis Group seeking approval of CT colonography (CTC) as a generalized screening tool for colorectal cancer among asymptomatic Medicare patients 50 years of age or older. The letter itself was a calm recitation of years of evidence collected through studies and trials of CTC in various patient groups, including the large, multicenter ACR Imaging Network (ACRIN) trial recently completed.

The letter was sent in response to a call from CMS for comment on a national coverage analysis of CTC. The letter, sent under the sponsorship of the ACR, the Society of Gastrointestinal Radiologists, and the Society of Computed Body Tomography & Magnetic Resonance, hardly appeared, on its face, to mark a watershed event, but the response to CMS may have been one.

imageJudy Yee, MD

CTC, commonly called virtual colonoscopy (a name that the ACR is trying to discourage), has been on the horizon for years. Its practitioners have patiently developed it through several generations of CT scanners and have seen its utility and accuracy increase with the introduction of 2D and 3D postprocessing software and workstations. For all this, CTC has remained largely an out-of-pocket expense. At the same time, over 60% of those at risk for colon cancer are going unscreened.

imageBibb Allen, MD

Now, that could change. If CMS approves CTC as a generalized screening tool, the impact on patients, payors, radiology groups, and certain nonradiology physicians could be momentous, both clinically and financially.

Events Prior to the Letter

While she was not a signatory to the June 18 letter, Judy Yee, MD, was one of its authors. She and her colleagues worked quickly to prepare the letter once CMS called for comment on CTC. She says, “There was a short window. It was 30 days.”

Yee is chief of radiology at the San Francisco VA Medical Center and is also professor and vice chair of the department of radiology and biomedical imaging at the University of California–San Francisco (UCSF). She has been a pioneer of CTC through studies at the VA and elsewhere. She has also developed national guidelines for performing CTC screening, and she teaches CTC at the UCSF medical school.

Yee says that a rapid succession of events stimulated the CMS call for comment and the writing of the June 18 letter. First, in late 2007, the results of the ACRIN trial were released. They showed excellent performance for CTC as a screening tool, Yee says, with sensitivity rates of 90% and specificity rates of 86% for precancerous polyps of 10 mm or more. These rates were comparable to those for the gold standard in colorectal-cancer detection, the optical colonoscopy (OC), Yee adds.

The second stimulus, Yee says, was the 2007 publication of a study1 directly comparing CTC with OC; it found similar detection rates for advanced adenomas. A significant factor in that study, Yee adds, was that the number of polypectomies was four times higher in the OC-only group than in the CTC group, meaning that polyp removal for the CTC patients who later underwent OC and surgery was more efficient.

The third stimulus behind the CMS call for comment and the June 18 letter was perhaps the most critical, Yee says. That came in March 2008, when the American Cancer Society added CTC to its list of screening options for colorectal cancer. “For the first time, there was endorsement of CTC as a valid option for screening for colorectal cancer,” Yee says.

The Clinical Impact

While CMS won’t act on CTC approval for screening until all comments have been analyzed, Yee says that she’s optimistic. “My take on this is that CTC has really been proven,” she says. “I think the ACRIN trial showed this is an excellent test, with a less invasive option for getting the screening done.”

If CTC is approved by CMS—and if other payors follow the CMS lead with their own approval—then the clinical picture of colorectal cancer in the United States could be hugely altered. For one thing, Yee says, many more patients will be screened for precursor polyps before their cancers can develop.

Because OC requires an instrument to be inserted into the colon, most asymptomatic patients opt out of screening. “Currently, less than 40% of those who should be screened are actually getting screened,” Yee says. “This is with the options of colonoscopy, barium enema, or flexible sigmoidoscopy.”

Most people continue to rely on a routine fecal occult-blood test (FOBT), but the