Virtual colonoscopy: What is its role in cancer screening?

The virtual colonoscopy (CT colonography, or CTC) could make life just a little bit easier when it comes to discussing colorectal cancer screening options with your patients. After all, what patient wouldn’t like to hear that there is an alternative to the colonoscopy that doesn’t require sedation, IV injections, or a scope?

The reality, though, is that a number of roadblocks stand between the CTC and its inclusion in the battery of colorectal screening tools we typically discuss with our patients. Among the barriers: Mixed results from research studies evaluating the sensitivity and specificity of the CTC^1-3 and a decision by many insurance plans not to cover the procedure, deeming it “experimental.”⁴

More research is undoubtedly needed, and some is already underway. The American College of Radiology Imaging Network has conducted a large scale, double-blind study,⁵ with results expected later this year. In the meantime, though, counseling your patients on their options will hinge on your knowledge of the advantages and disadvantages of the CTC and what the research—to date—tells us about its usefulness.

Like a colonoscopy, it offers a fly-through view

The CTC, which uses helical CT to capture 2D axial images that can be converted into a 3D view, allows the radiologist the same type of colon “fly through” view that a gastroenterologist would see using a colonoscopy (FIGURE).⁶ Among its pluses: It requires no anesthesia and is noninvasive, so it’s likely to appeal to patients who have a strong fear of colonoscopy. (See “What patients can expect during a CTC”) Another potential plus: While full bowel cleansing is still required, recent investigations have studied new “prep-less” CTC options consisting of a low residue diet with multiple doses of liquid barium without catharsis.^7-9

CTC also offers a viable screening option for certain patient populations. Specifically, it’s already regularly being used in those who have had an incomplete colonoscopy or who have an obstructing carcinoma.^10-12 CTC can also be used to screen elderly patients who have contraindications to conscious sedation or medical problems that preclude them from invasive procedures.

FIGURE
“Fly-through” via virtual colonoscopy

A 2D color reconstruction “fly-through” showing a large pedunculated polyp (left) and a large sessile polyp (right).On the downside, there is always a concern about the possible deleterious effects of radiation whenever an imaging technology is involved. The average person in the US gets about 3 mSv of radiation per year from the environment. This compares with about 10 mSv from a CT of the abdomen, 0.1 mSv from a chest x-ray, 0.7 mSv from mammography, or 5 to 7.8 mSv from CTC.^13,14 Even though the radiation dosage currently used in CTC is safe, studies examining CTC with lower ionization have produced very hopeful results.¹⁵ In fact, a recent study by Brenner et al found that in terms of radiation from CTC and its ability to detect polyps, the benefits far outweigh any risks.¹⁶

As you might expect, the cost of a CTC is on the higher end of the colorectal cancer screening spectrum, though it is comparable with a colonoscopy. Fecal occult blood testing is the cheapest, with a cost, on average, of $10 to $20. Flexible sigmoidoscopy is about $150 to $300, double-contrast barium enema is about $250 to $500, and both colonoscopy and CTC are about $800 to $1600. However, CTC is currently not covered under most insurance plans, but it’s starting to gain acceptance as a reimbursable procedure. In fact, the Centers for Medicare and Medicaid Services has recently published CPT codes for CTC and even more recently made the professional components of both diagnostic and screening CTC fully reimbursible.