Virtual Colonoscopy Gaining New Respect as a Sensitive and Cost-Effective CRC Screening Tool

For the past few decades, optical colonoscopy has been the gold standard in colon cancer screening. However, recent studies have shown that virtual colonoscopy may be the safest and most cost-effective colon cancer screening method available. Cancer Care & Economics (CC&E) recently spoke with Abraham H. Dachman, MD, professor of radiology at the University of Chicago Hospitals. A nationally recognized expert in virtual colonoscopy, Dr. Dachman explained why this emerging technology deserves a prominent place in screening for colon cancer.

CC&E: Has virtual colonoscopy finally gained recognition as a cost-effective screening tool?

DR. DACHMAN: Yes. We've seen virtual colonoscopy evolve from basically being considered a research technology into an accepted, clinically viable procedure. The positive predictive value rates published to date, as well as results from ongoing screening programs, prove that virtual colonoscopy is a very sensitive and cost-effective screening tool when targeting individual polyps about 6.0 mm and greater. According to recent studies, targeting smaller lesions does little to reduce the incidence of colorectal cancer [CRC] and results in unnecessary costs. [See ONI, May 2007, page 54.]

CC&E: What improvements have we seen in virtual colonoscopy?

DR. DACHMAN: For one, advances in technology have made virtual colonoscopy a faster, more comfortable, and more automated exam. We now have dedicated rectal tubes and dedicated pressure-controlled carbon dioxide insufflators that are extremely safe. We also have faster CT scanners that essentially eliminate the imaging problems that arise with respiratory motion.

The computers and networks to reconstruct and send the images through programmable automation controller (PAC) systems to dedicated workstations are vastly improved. We have better software to interpret the cases using a host of techniques that include 2D and 3D, as well as novel views with interesting new reading tools for the radiologist.

The combination of these factors has resulted in the potential to learn how to read virtual colonoscopy in a time-
efficient manner, and although there is still a long learning curve, an experienced reader can interpret most cases in 10 to 15 minutes.

CC&E: For various reasons, optical colonoscopy might not view the entire bowel, leaving an incomplete exam. Is this an issue with virtual colonoscopy?

DR. DACHMAN: No, essentially it's not. Studies examining the causes of incomplete optical colonoscopies indicate reasons such as partially obstructing tumors, benign strictures, and adhesions from previous surgery. However, in virtual colonoscopy, patients with obstructive lesions can be faithfully traversed by refluxing carbon dioxide gas or room air retrograde into the remainder of the colon, reliably evaluating not only the full extent of the abnormality but also looking for synchronous polyps and masses to the terminal ileum. Simply put, a virtual colonoscopy can visualize 100% of the colon surface because of its ability to navigate in both directions.

CC&E: Bowel prep is often cited as a discouraging factor in compliance with optical colonoscopy. Is bowel prep with virtual colonoscopy gentler?

DR. DACHMAN: Currently, most practitioners prefer using a saline cathartic rather than a gavage. And they prefer that the patient have some additional tagging agent to identify residual fluid and stool. So there still exists a degree of discomfort in the prep stage.

That said, there are investigators working on a reduced, gentler prep. In fact, one company has now put out a saline cathartic in a standard reduced dose dedicated specifically for virtual colonoscopy. Undoubtedly, bowel prep for virtual colonoscopy will become a gentler, more refined process over time.

CC&E: What kind of start-up costs could a facility expect in initiating a virtual colonoscopy program?

DR. DACHMAN: The set-up cost is almost negligible. The most expensive piece of equipment is the CT scanner, which any facility doing radiological work already has. The next highest cost is a workstation, and, again, facilities doing radiological exams routinely employ workstations. The only secondary expenses are a software package for interpreting virtual colonoscopy, a carbon dioxide insufflator, and the disposables, the tagging agent, and the tubing. The main investment is actually the time and energy needed to learn how to deliver and read the examination.

CC&E: Is the payer community embracing virtual colonoscopy?

DR. DACHMAN: Currently, about 45 states partially reimburse for virtual colonoscopy. Each state has slightly different regulations. The most common scenario is reimbursement for virtual colonoscopy in the event of an incomplete optical colonoscopy when done for a diagnostic indication. Acceptance as a fully reimbursed screening modality will evolve as more data are published in scientific journals and more virtual colonoscopy programs are initiated.

CC&E: Imaging technologies always provoke debate over their true value. Any closing thoughts on the future of virtual colonoscopy?

DR. DACHMAN: Some of the pitfalls and concerns that have been raised about computer-aided mammography and lung nodule detection have some analogies to virtual colonoscopy, but also some important differences. As I mentioned, recent studies have demonstrated the efficacy and predictive value of virtual colonoscopy, within the scope of its intended use in screening.

Looking forward, I see virtual colonoscopy being routinely employed on a national level, regularly integrated with stool tagging and computer-aided detection. I also see virtual colonoscopy providing a screening option that will encourage more uniform adherence to American Cancer Society screening guidelines, which will ultimately help reduce the incidence of colon cancer.