Authors' objectives:

This Assessment reviews evidence on the effectiveness of CT colonography as an alternative to colonoscopy for the purpose of colon cancer screening.

Authors' results and conclusions: Based on the available evidence, the Blue Cross and Blue Shield Association Medical Advisory Panel made the following judgments about whether CT colonography for colon cancer screening meets the Blue Cross and Blue Shield Association Technology Evaluation Center (TEC) criteria. 1. The technology must have final approval from the appropriate governmental regulatory bodies. CT colonography may be performed using any CT scanner capable of producing helical (spiral) thin-section images ( <5 mm). More recent studies have been conducted using commercially available multidetector-row (multislice) helical CT scanners that facilitate faster image acquisition and thinner sections. The 2D cross-sectional CT images may be interpreted directly, and software algorithms using 3D reformatting techniques may also be used to facilitate interpretation. 3D reformatting software may be cleared through the U.S. Food and Drug Administration (FDA) for this specific application. For example, the Viatronix V3D-Colon virtual colonoscopy system (Viatronix, Inc., Stonybrook, NY) was cleared for marketing by the FDA via the 510(k) process on April 19, 2004, for use as a screening tool in detecting colon cancer. 2. The scientific evidence must permit conclusions concerning the effect of the technology on health outcomes. The current evidence consists of studies evaluating the sensitivity and specificity of CT colonography compared to either colonoscopy alone or a colonoscopy aided by CT colonography results. In this Assessment, 11 studies evaluating diagnostic performance at a per-patient level of analysis at specific minimum size thresholds met study selection criteria for this review. Included studies were prospective studies that compared CT colonography and optical colonoscopy to a valid reference standard (usually colonoscopy), provided per-patient analysis allowing calculation of sensitivity and specificity of CT colonography, and reported on at least 50 patients. Overall, sensitivities were quite variable between studies, from as low as 35% to as high as 100% for detecting patients with 10 mm or larger lesions. The larger studies with more stable estimates of sensitivity ranged from 55% to 94%. Specificities were less variable, and most studies reported sensitivities greater than 90%. At a smaller size threshhold of detection CT colonography was both less sensitive and less specific. Variable performance of CT colonography may be associated with interpreter experience or other technical factors. Such evidence does not allow conclusions on the effect of CT colonography in improving health outcomes, however. Positive findings on CT colonography require referral for colonoscopy to confirm findings and remove polyps. The appropriate minimum size of polyp that should be referred and the appropriate screening interval are unknown. It would defeat the purpose of initial noninvasive screening to refer patients with any polyp for colonoscopy, because the prevalence of polyps is so high that a large proportion of patients would need to undergo both procedures. Because known polyps are left behind, and sensitivity for small polyps is known to be less than colonoscopy, CT colonography is meant to be used more frequently than colonoscopy in a screening program. 3. The technology must improve the net health outcome. There is no direct evidence as to whether CT colonography improves health outcomes. However, the evidence evaluating colonoscopy, its principal comparator, is also indirect. Colonoscopy has become an accepted mode of colon cancer screening through understanding of the natural history of colon cancer and its role in other proven methods of colon cancer screening. 4. The technology must be as beneficial as any established alternatives. The current evidence does not allow conclusions as to the comparative efficacy of CT colonography and colonoscopy. Comparison of sensitivity and specificity with colonoscopy is incomplete evidence, because the 2 techniques are intended to be used differently. The bowel preparation currently required for CT colonography is the same as conventional colonoscopy, and depending on the criteria for referral, a variable proportion of patients require colonoscopy, which necessitates another bowel preparation. CT colonography only identifies for removal polyps of a certain minimum size threshhold, and is meant to be used more frequently. It is uncertain what the appropriate size threshhold for referral and frequency of screening is appropriate. Actual longitudinal studies or modeling studies are needed to assess comparative efficacy in preventing colon cancer mortality. Improvements in the technical aspects of CT colonography include developments in stool tagging and digital subtraction, which may obviate the need for bowel preparation. In such a case it might then be appropriate to compare CT colonography to one of the less-invasive colon cancer screening techniques. 5. The improvement must be attainable outside the investigational settings. Diagnostic performance of CT colonography is variable in the studies, possibly due to differences in interpreter experience and variability in other technical aspects of performing the test. Standards of performance are yet to be developed. It is likely that diagnostic performance in the community may also vary. While there is no direct evidence of improvement of health outcomes with use of CT colonography, poor diagnostic performance virtually precludes any possible positive effects of the technology.

Authors' recommendations: Based on the above, CT colonography as an alternative to colonoscopy for the purpose of colon cancer screening does not meet the TEC criteria.

Authors' methods: Review

Project Status: Completed

URL for project: http://www.bcbs.com/blueresources/tec/contact-tec.html

Year Published: 2004

English language abstract: An English language summary is available

Publication Type: Not Assigned

Country: United States

Organisation Name: BlueCross BlueShield Association

Contact Address: BlueCross BlueShield Association, Technology Evaluation Center, 225 North Michigan Ave, Chicago, Illinois, USA. Tel: 888 832 4321

Contact Name: tec@bcbsa.com

Contact Email: tec@bcbsa.com

Copyright: BlueCross BlueShield Association (BCBS)