Despite challenges, interest grows in CT colonography
Trial could trigger change in demand, reimbursement
While it is not without risks, optical colonoscopy (OC) has long been the gold standard for colorectal cancer screening. The problem is that most Americans fail to undergo screening as recommended, probably because it is an invasive procedure that requires what many consider to be an onerous preparation regimen designed to cleanse the colon. For that precise reason, there is growing interest in CT colonography (CTC) as an alternative screening procedure that could potentially encourage many more people to undergo colorectal screening and ultimately save lives.
While early data regarding the use of CTC showed that the procedure did not approach the accuracy level of OC,1 the procedure has undergone refinements and improvements in recent years. Newer data are more encouraging. For example, a non-randomized study comparing the use of CTC with OC for the detection of advanced neoplasia found that the two screening procedures resulted in similar detection rates.2
A co-author of that study, Perry Pickhardt, MD, associate professor of radiology at the University of Wisconsin Medical School in Madison, has extensive experience with CTC in part because he has received special authorization from local medical providers to be reimbursed for the procedure. "The benefit of adding another effective option like CTC is that more folks will come off the screening sidelines," he says. "Our experience is that many folks are reluctant to undergo OC for primary screening, [but] these folks are often willing to undergo CTC."
However, in other states reimbursement for CTC is relatively rare except in cases where OC cannot be completed or OC is considered too risky for the patient to undergo. Further, no current guidelines recommend CTC as a primary screening alternative. Consequently, for many providers, CTC is a private pay option and is therefore in limited use.
CTC is a non-invasive test and is therefore generally less expensive to carry out than OC. However, part of the problem is that if the test identifies polyps that need to be removed, the patient then must be referred for OC as well so the polyp(s) can be removed. In Pickhardt's study, when CTC revealed polyps that were at least 6 mm in size, these patients were referred for OC to have those polyps removed. This referral occurred in 7.9% of the 3,120 patients who underwent CTC.2
However, gastroenterologists are worried that some radiologists performing CTC may be inclined to leave small polyps intact, rather than refer patients on to a second procedure. "Small polyps being ignored, we think is very dangerous," emphasizes David Johnson, MD, FACG, FACP, immediate past president of the American College of Gastroenterology and professor of medicine and chief of gastroenterology at Eastern Virginia School of Medicine in Norfolk. He points out that researchers have looked at the impact of disregarding smaller polyps (6-9 mm), and they have concluded that the practice can miss some high risk lesions.3 However, Pickhardt counters that his approach with regard to small polyps (removing polyps that are 6 mm or larger) is sound medical practice. "The risks involved with sending a patient to OC for a small polyp outweigh the inherent risks of the polyp itself," he says.
Concerns with regular CTC scans
Johnson also raises the concern of radiation exposure involved with undergoing regular (every five years) CTC scans. "The concern is that radiation is just going through the roof in terms of exposure," says Johnson, noting that many people undergo diagnostic studies with regularity and especially abdominal CT scans. "If you superimpose on that [exposure] these screening tests with regularity, then you really start to ramp up the exposure risk for radiation."
The type of abdominal scan required for CTC requires 10-20 mSv of radiation, but Johnson points out that the dosage must, in some cases, be doubled for people who are obese. However, Pickhardt believes that the concerns about radiation exposure have been greatly exaggerated and that other risks should be considered as well. "The tiny theoretical risks associated with radiation at CTC pale in comparison to the very real risks of perforation and bleeding at OC," he says.
Many concerns about CTC are related to the fact that studies looking into the technology have been small and results have been relatively inconsistent, depending on which centers are involved. However, these concerns should be addressed this year when the results of a large, multi-center trial are unveiled. The American College of Radiology Imaging Network (ACRIN) National CT Colonography Trial enrolled more than 2,300 participants at 15 sites. Each participant has undergone CTC followed by OC in the same day, so the effectiveness of the two techniques can be compared. C. Daniel Johnson, MD, a professor of radiology at Mayo Medical School in Rochester, MN, is leading the effort. He has indicated that he anticipates that the trial will settle many of the questions and concerns regarding CTC.
In fact, CTC technology, and associated CAD programs to assist the radiologist in locating areas of interest, have advanced since the ACRIN trial was launched in 2005, according to Pickhardt. "ACRIN represents the low end of the performance level that I would expect in the 'real world,'" says Pickhardt. Nonetheless, if the results suggest that CTC is comparable to OC as a screening modality, they could lead to more willingness on the part of guideline-writing committees to recommend CTC. That, in turn, could encourage more payers to reimburse for the test and more people to get screened.
"That is a significant trial," observes David Johnson, "and the data look reasonably promising."
References
- Cotton P, Durkalski V, Pineau B, et al. Computed tomographic colonography (virtual colonoscopy): a multicenter comparison with standard colonoscopy for detection of colorectal neoplasia. JAMA 2004; 291:1,713-1,719.
- Kim D, Pickhardt P, Taylor A, et al. CT colonography versus colonoscopy for the detection of advanced neoplasia. N Eng J Med 2007; 357:1,403-1,412.
- Hurr C, Chung DC, Schoen RE. et al. The management of small polyps found by virtual colonoscopy: results of a decision analysis. Clin Gastroenterol Hepatol 2007; 5:237-244.
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