Both Dr Pickhardt and Dr Joseph Ferrucci criticize the Cotton et al study because it primarily used 2D images and their trial ended in October 2001, whereas Pickhardt et al’s started in May 2002.22 With so much dependent on software issues, the interval is significant. In addition, the study by Dr Cotton and his colleagues used older CT and insufflation technology and several of the centers involved in the studies only had to show familiarity with the procedure, but no demonstrated ability in reading CTC images.22 Thus, both technical and reader issues were significant. Similarly, in the study by Rockey et al, the issue of reader inexperience was present, as was the fact that neither stool nor fluid tagging was used.22
Remove that polyp? With virtual colonoscopy, it’s not automatic
When an adenomatous polyp of any size is found during a colonoscopy, the polyp is removed. Thus the diagnostic and therapeutic functions are married in colonoscopy. However, CTC only allows detection of these polyps, thus raising the question as to which size polyps should be reported and then removed by doing an additional colonoscopy. The issue of what size polyps have malignancy potential has been discussed extensively in the literature.31-33
It’s also a hotly debated topic in the literature for colorectal cancer screening, especially when any mention of CTC comes up. Every year, about 1% of polyps larger than 10 mm progress to colorectal cancer and there is agreement that these should be removed.34 However, there is considerable debate over the 6 to 9 mm category.34-36 Several trials have shown that the incidence of polyps between 6 to 9 mm progressing into colorectal cancer approaches, but is definitely less than 1%.37 Even the American Gastroenterological Association acknowledges that the risk of developing colorectal cancer from a polyp 6 to 9 mm remains uncertain.21
Thus, while it’s clear that polyps larger than 10 mm pose a significant enough risk to warrant removal, the data is equivocal—or absent—on what to do about polyps in the 6 to 9 mm category.
Another important variation between Pickhardt et al’s study and those by Drs Cotton and Rockey and their colleagues is the use of oral contrasts for stool tagging.23 A unique aspects of Pickhardt et al’s study was the aggressive bowel preparation using 2 types of oral contrast (water soluble and barium) for stool tagging. This allowed the computer to electronically separate and subtract residual stool from soft tissue structures improving image quality dramatically.1 This elaborate patient preparation has not been done by anyone else. Many contend that what Pickhardt et al achieved was a paradigm of the best CTC can be under ideal circumstances, technology, and expert interpretations and if not done in this manner, the results would get murky with diffuse application.23 This again emphasizes the importance of recognizing the evolving technology and protocol for CTC.
Much-needed research is underway
Until results of the caliber that Pickhardt et al achieved are reproducible locally, many insurance companies will delay coverage for screening CTC. For most areas, CTC would be about $1000 out of pocket cost for the patient. It seems likely that most patients would not opt for CTC when insurance companies cover other screening procedures.
The American College of Radiology Imaging Network has conducted a very large-scale double-blind study of CTC effectiveness in a screening population involving 15 institutions and 2300 participants.5 The results of this trial, expected out this summer, will surely influence CTC’s acceptance both by the medical community and by third party payers. Until then, family physicians will need to consider the use of CTC on a case-by-case basis.
American Cancer Society guidelines
Colorectal cancer mortality can be significantly reduced through proper screening.18,24-27 The American Cancer Society’s guidelines for screening28 indicate that beginning at age 50, both men and women with average risk factors should have one of the following:
- yearly fecal occult blood test
- flexible sigmoidoscopy every 5 years
- yearly fecal occult blood testing and flexible sigmoidoscopy every 5 years
- double-contrast barium enema every 5 years, or
- colonoscopy every 10 years.
A positive finding for any of the first 4 should prompt a colonoscopy.
CORRESPONDENCE
Jaspal Singh Ahluwalia, MD Walter Reed Army Medical Center, 6900 Georgia Avenue NW, Washington, D.C. 20307 E-mail: jaspal.ahluwalia@us.army.mil