Next, consider the economics of dual modality screening. The find rate for polyps greater than 6mm using VC is just under 30%. In our practice, using optical colonoscopy, polyps were found in over 45% of procedures (see Table 1), and 36% of patients had polyps exceeding the VC detection threshold. Conceivably, one third of all VCÌs could lead to a conventional colon-oscopy; polyps smaller than 6 mm would be missed, though the risk of these small polyps is thought to be low. The economics of VC now become clear: the higher the rate of proceeding to colonoscopy and polypectomy at any time, the lower the efficiency of this tool. This is one of the factors that has prevented VC from being officially recognized by Medicare and other third parties as a reimbursable screening method.

The convenience [of VCs] will be very attractive to many who would otherwise not consider screening.

Finally, a recent National Academy of Sciences panel raised the issue of radiation exposure, citing a single CT scan as conveying a lifetime risk of 1 in 1000 for cancer. If true, this exceeds the risk of death or serious morbidity from conventional colonoscopy. Despite these concerns, the element of convenience will be very attractive to many who would otherwise not consider screening. Any legitimate tool that increases the number of those being screened will save lives.

Table 1. Colon polyp detection rates at Charlottesville Gastroenterology Associates. Data were obtained over a 3-month study period 10/04 Ò 12/04. Study cohor includes screening and diagnostic colonoscopies.
	At Martha Jefferson Hospital, we have been using virtual colonoscopy for over five years to complement optical studies. It is likely that the usage will increase as technical obstacles are overcome. Our medical imaging department and our gastroenterologists work closely together on an ongoing basis to define and implement the best possible screening strategy for our community.

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