Clinical Results

CTC researchers have developed several conventions for standardizing result reporting (Fenlon et al. 1999; Dachman and Zalis 2004). Results are reported on a per polyp as well as a per patient basis. Results based on per poly analysis are the most rigorous as they imply direct comparison to colonoscopy. Per patient analysis, however, is the more clinically relevant parameter in terms of referral of the patient for therapeutic optical colonoscopy. Polyp detection rates are usually grouped according to size as under 6 mm in diameter, 6-9 mm and 10 mm or greater. Polyp location is given either by anatomical colon segment (six or eight segments) or by recording the linear colon center line distance from the anal verge from workstation software. Polyp measurements are usually given as the longest linear dimension either by 2D or 3D viewing and there is also an emerging consensus that some form of a confidence limit modifier may be of some clinical merit.

To date, the most important published result has been that of a multi-center trial of screening in asymptomatic adults from the U.S. Department of Defense. (Pickhardt et al. 2003). In that prospective study of 1233 patients, CTC detected 96% of polyps 8 mm or greater, was more accurate than optical colonoscopy, and found 55 polyps and one of 2 cancers missed by optical colonoscopy. CTC also gave a negative predictive value of 98% for any polyp greater than 10 mm in size, and showed that over 50% of patients had no polyps whatsoever present in their colon. The excellent results in that study were considered to be multi-factorial in nature and included the use of primary endoluminal 3D viewing, aggressive double dose phosphosoda bowel preparation, knowledgeable radiologist readers, and the use of a novel segmental unblinding technique which produced a new consensus 'ground truth' by direct virtual and optical colonoscopic correlation. As a result of that study, gastroenterologists in the U.S. and their national professional organizations conceded that CTC was a technique that was likely to be of wide value and encouraged its "use" by gastroenterologists. However, a subsequent smaller study conducted by U.S. gastroenterologists several months later gave much poorer results (Cotton et al. 2004). However, that study was widely discredited by CTC radiologist researchers because of outmoded techniques and flawed study execution (Ferrucci et al. 2004; Pickhardt 2004; Halligan et al. 2004). Nevertheless, some doubt as to the generalizability of CTC performance was raised and the issue was left open as to whether or not additional studies of CTC in screening populations were really required. Two such large multi-center trials are underway as of this writing, one in the U.S conducted by the American College of Radiology Imaging Network (ACRIN) and another in the U.K. carried out for the National Health Service by the Special Interest Group for Gastrointestinal and Abdominal Radiology (SIGGAR). However, the results of these two trials are not likely to be widely available before 2006-2007. In the meantime, rapid further technical advances in CTC including the use of newer 16-64 slice multi-row detector scanners, laxative free colon cleansing schemes, and computer aided detection will become more widespread. Thus even these studies now well underway are destined to be characterized as outdated by the time their results are eventually published.

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