Widespread reimbursement in the private sector is not here yet, however, since many major insurance companies consider CTC an experimental procedure.4 This hesitance on the part of the private sector is understandable, as we found when we undertook a search of the literature.
Methods
We conducted a thorough and systematic search of PubMed for English-language articles from 1994 to 2006. Search terms included “CT colonography,” “virtual colonoscopy,” “CT colonoscopy,” “colography,” and “CT pneumocolon.”17 The general focus was on original research articles, but meta-analyses and review articles were also considered. In addition, we conducted general Internet searches to discern the general public’s view on this technology.
The research is mixed—specificity/sensitivity values vary
Research has shown that colorectal cancer arises in adenomatous polyps and that detection and removal reduces mortality for this cancer.18,19 Since 1994, when Vining et al first described the concept of CTC,6 numerous studies have compared its polyp detection rate with the gold standard, colonoscopy. The most recent are 3 large, multicenter prospective trials comparing the sensitivity and specificity of CTC against colonoscopy for adenomatous polyp detection.1-3 These 3 studies have not been consistent in their findings. One study showed very favorable results,1 but the other 2 showed unfavorable results (TABLE).
In December 2003, Dr Perry Pickhardt and his colleagues published the first multicenter prospective study comparing CTC with colonoscopy on a large, asymptomatic population.1 That study was performed in 3 medical centers and included 1233 subjects with a mean age of 57.8 years. All of the subjects underwent same-day CTC and colonoscopy. Each CTC was interpreted using both 2D and 3D imaging techniques. The results were very encouraging. CTC had a 93.8% sensitivity for adenomatous polyps at least 10 mm in diameter, 93.9% sensitivity for those at least 8 mm in diameter, and 88.7% sensitivity for those at least 6 mm in diameter. (For more on polyp size, see “Remove that polyp? With virtual colonoscopy, it’s not automatic,”.) The specificity for those polyp size categories was 96.0%, 92.2%, and 79.6%, respectively. The study concluded that CTC compared well with colonoscopy in the detection of adenomatous polyps in asymptomatic adults.
In April 2004, Dr Peter Cotton and his colleagues published the second multicenter, prospective study comparing CTC and colonoscopy in terms of adenomatous polyp detection for a screening population.2 The study took place at 9 medical centers and had 615 patients ages 50 and older who had both CTC and colonoscopy done on the same day. The researchers found that CTC had a sensitivity of 55% for those at least 10 mm in size and 39% for polyps at least 6 mm in size. They concluded that CTC technology was not ready for mainstream clinical use until a significant amount of enhancement took place in the use of this technology.
In January 2005, Dr Don Rockey and his colleagues published a multicenter study comparing CTC and colonoscopy at 14 sites.3 They had 614 patients with an average age of 57.4. They also found CTC to be significantly less sensitive for detecting polyps both >10 mm and >6 mm when compared with colonoscopy.
TABLE
Multicenter trials compared colonoscopy and virtual colonoscopy polyp detection rates
| PB COTTON ET AL2 (JAMA) | PJ PICKHARDT ET AL1 (NEJM) | DC ROCKEY ET AL3 (LANCET) | |
|---|---|---|---|
| Number of sites | 9 | 3 | 14 |
| Dates of study | April 2000–Oct 2001 | May 2002–June 2003 | Dec 2000–Feb 2004 |
| Number of patients | 615 | 1233 | 614 |
| Patient age (mean) | 61 | 57.8 | 57.4 |
| Sensitivity & specificity of detecting lesions ≥6 mm | Sensitivity: 39.0% Specificity: 90.5% | Sensitivity: 88.7% Specificity: 79.6% | Sensitivity: 51.0% Specificity: 89.0% |
| Sensitivity & specificity of detecting lesions ≥10 mm | Sensitivity: 55.0% Specificity: 96.0% | Sensitivity: 93.8% Specificity: 96.0% | Sensitivity: 59.0% Specificity: 96.0% |
The discrepancy may be a matter of software and protocols
Dr Pickhardt and his colleagues attribute part of their success in CTC to the particular software they used, which can render 3D images better than almost any other program available.20 A report issued by the American Gastroenterological Association says that Pickhardt et al’s use of primary 3D interpretation differs from most currently performed protocols.21 If Pickhardt et al’s results can even partly be attributed to use of new software, then it seems prudent to change the protocols to whatever works best in light of the evolving technology. The protocols must remain flexible until appropriate results are achieved and repeatable.
In addition, there are many other variables that could account for these results including a younger screening population, mostly composed of military families, the use of stool and fluid tagging (advanced techniques that improve accuracy and decrease the need for a completely clean bowel), or the aggressive, double-bowel preparations given before the procedure.1