May 11, 2009 (Boston, Massachusetts) — A study using computed tomography colonoscopy (CTC) found that the technique can reliably detect polyps as small as 6 mm in approximately 92% of cases. The finding was presented here at the American Roentgen Ray Society (ARRS) 2009 Annual Meeting.
In the study, conducted at the University of Wisconsin Medical School, CTC (also known as virtual colonoscopy) detected 667 (91.6%) of 739 lesions in 479 patients presenting for colorectal screening.
This study was based on an initial population of 5124 patients screened with CTC. Of this group, 639 patients (12.5% of the total) were found to have a polyp 6 mm in size or larger. Of those, 479 patients received subsequent optical colonoscopy for confirmation and polypectomy to determine positive predictive value (PPV).
"I feel that our data support the use of [CTC] as a primary screening tool for colon cancer," lead study researcher Steven Wise, MD, from the University of Wisconsin School of Medicine and Public Health in Madison, told Medscape Radiology. "We propose that it be used as an initial screening test so that the patients who do have positive CTC screening exams can then be selected out for optical colonoscopy and subsequent polypectomy."
To function as an effective screening tool, CTC must not only be sensitive for the detection of clinically relevant lesions, classified in this study as polyps 6 mm or larger, it must also demonstrate a low false-positive rate and high concordance with optical colonoscopy, he said.
The study found that the PPV of CTC did not vary according to polyp size. Approximately 92.7% of polyps 10 mm or larger were detected by CTC. The PPV for polyps 6 to 9 mm was similar, at 90.1%. However, researchers did find that polyp morphology plays a role in different PPV findings. Lesions classified as mass or carpet lesions were detected 100% of the time. However, flat lesions were identified in only 76.8% of cases.
Dr. Wise said his research stems from his association with the highly regarded diagnostic radiology team of coauthor Perry Pickhardt, MD, and others at the University of Wisconsin. "Dr. Pickhardt's body of work is one of the largest . . .in the field of diagnostic radiology in colon cancer," Dr. Wise said. "Much of it contributes to this idea that CTC is going to be well-suited to serve as a screening modality for cancer. Our data here demonstrate that if we call it at [CTC], the optical colonoscopist can be confident that they will find a lesion where we said it was."
Reimbursement and Training Lacking
Study researchers suggest that CTC might help overcome 1 of the limiting factors for optical colonoscopy. "Optical colonoscopy is an effective screening tool, but it is currently not being used for the majority of the eligible screening population," Dr. Wise said. "There are not enough endoscopists, so that also limits its application."
However, CTC faces its own limiting factors. "CT colonography is used as a screening tool already, but not routinely yet," explained session moderator Abraham Dachman, MD, director of computed tomography at the University of Chicago Medical Center in Illinois. [The lack of its] widespread use is not a medical deficit but a fiscal problem. "The reimbursement issue is the hottest topic now with regard to CTC," Dr. Dachman told Medscape Radiology.
Until July 2004, insurance companies fully reimbursed radiologists for performing virtual colonoscopy. But in July 2004, virtual colonoscopy was reclassified with category 3 diagnostic codes.
"As a result of that, all insurance and Medicare stopped paying for virtual colonoscopy. We have been fighting an uphill battle ever since to reinstate and expand insurance coverage," Dr. Dachman said.
Today, most insurance companies pay for CTC only for diagnostic purposes, not for screening purposes. The American Cancer Society endorsed virtual colonoscopy in late 2008, but reimbursement has not followed suit. And thus far, the Centers for Medicaid and Medicare Services (CMS) have denied reimbursement for virtual colonoscopy. But that fight is still ongoing, with the American College of Radiology pursuing a positive reimbursement stand. Congressional hearings in March 2009 focused on the pending final decision from CMS, which will be announced later this month.
Another limiting influence on the overall success of CTC has to do with radiology training for the technique. In his keynote address at the ARRS session on genitourinary imaging, during which Dr. Wise presented his study, Dr. Dachman said: "I have significant concerns about radiologist training and certification when it comes to CTC. The average radiologist cannot usually reproduce the kind of data published by Pickhardt et al and by Dr. Wise here. Other centers show acceptable or good results, but they often do not reach that level of sensitivity and have lower specificity."
The final CMS decision will certainly influence the rate of use of CTC for screening, but the fight for optimal training will linger. Dr. Dachman said: "I think CMS will eventually change its mind, but I think we have to be proactive as radiologists to offer high-quality training to the radiologists. If you try to institute a virtual-colonoscopy program and your radiologists can't get it right, you will lose credibility."
Dr. Wise has disclosed no relevant financial relationships. Coauthor Dr. Pickhardt has disclosed financial interests with Viatronix, Medicsight, Fleet, Covidien, Philips, and VirtuoCTC. Coauthor Dr. Kim has disclosed financial interests with Viatronix, Medicsight, and VirtuoCTC. Dr. Dachman is a consultant to iCAD Inc; GE Healthcare, Inc; and ACR Image Metrix, Inc.
American Roentgen Ray Society 2009 Annual Meeting: Abstract 110. Presented April 27, 2009.
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Cite this: ARRS 2009: Study Confirms Virtual Colonoscopy Is Reliable for Colorectal Cancer Screening - Medscape - May 11, 2009.