Virtual Colonoscopy Not Ready for Prime Time

Despite advances, it still has radiation risks and accuracy problems, new study finds

MONDAY, Nov. 1, 2004 (HealthDayNews) -- Virtual colonoscopy has been touted as a noninvasive and safe way of screening for colon cancer, but a new study adds to growing evidence that it's not yet ready to replace the standard colonoscopy.

In a standard colonoscopy, a scope is placed into the colon while the patient is sedated. The physician can see any cancerous or precancerous lesions and remove them on the spot. In a virtual colonoscopy, the patient has a CT scan that takes images of the colon, which are analyzed later. If any lesions are found, they have to then be removed during a traditional colonscopy.

For either procedure, patients have to fast and take a diuretic to clean their colon before the procedure can be performed.

In this study, researchers analyzed a mathematical model comparing virtual colonoscopy with standard colonoscopy on more than 100,000 patients and found that virtual colonoscopy was associated with more procedure-related deaths and cancer deaths than standard colonoscopy.

"Virtual colonoscopy has risks," said lead researcher Dr. Douglas Faigel, an associate professor of medicine from Oregon Health and Science University. "In addition, if you have a virtual colonoscopy and you see polyps, you have to have a regular colonoscopy with all of its risks."

Another risk of a virtual colonoscopy is cancer caused by the radiation used in the virtual colonoscopy, Faigel noted. "The risk to an individual patient is rather low, but over 100,000 patients you are going to see excess cancers," he said.

In addition, virtual colonoscopy misses more cancerous and precancerous lesions than standard colonoscopy, Faigel said. "If you miss important lesions, then you are going to have more patients get colon cancer after a virtual colonoscopy than a standard colonoscopy," he added.

Faigel's team found that out of 100,000, patients, there would be nine deaths from a standard colonoscopy and 30 deaths among patients who had a virtual colonoscopy.

There were 66 more colon-cancer-related deaths per 100,000 patients who had virtual colonoscopy, compared with standard colonoscopy, Faigel said. "It is up to the public to decide whether it is worth doing virtual colonoscopy, given the death rate, or not," he said.

Faigel presented his findings Nov. 1 at the American College of Gastroenterology annual meeting in Orlando, Fla.

Virtual colonoscopy is not safer or cheaper or more comfortable than regular colonoscopy, Faigel said. "I don't think virtual colonoscopy, as it is being done right now, really has a role," he added.

Faigel believes that if the level of radiation was reduced and the accuracy of the procedure was improved, then virtual colonoscopy would be comparable to standard colonoscopy.

"In addition, if you can get to a prepless virtual colonoscopy, which might increase compliance, then maybe it might be beneficial," Faigel said. "Right now, virtual colonoscopy is experimental, and patients should undergo one of the standard screening tests where we have data and we know it works."

This study is a simulation, cautioned Dr. Durado Brooks, director of colorectal cancer at the American Cancer Society. The risks associated with virtual colonoscopy seem a little high, he said.

"Virtual colonoscopy is really in its infancy, and it is in a state of rapid evolution," Brooks said.

But, he added, the data in this study reflects data from several years ago and therefore doesn't reflect virtual colonoscopy as it done today.

Brooks said that the amount of radiation used is getting lower and the accuracy is improving to near that of standard colonoscopy. However, the one study that found that virtual and standard colonoscopy were equally accurate has yet to be replicated, Brooks noted.

"Virtual colonoscopy is a work in progress," Brooks said. Today, virtual colonoscopy is not recommended as a screening tool for colon cancer by the American College of Radiology or other groups, so you should be screened by the proven methods recommended by the American Cancer Society, which include standard colonoscopy, Brooks said.

However, in the future, Brooks believes that virtual colonoscopy may become a proven and safe technique. "The field of virtual colonoscopy is in such rapid evolution. Within the next couple of years, a lot of the issues that are limiting it today are going to be improved," he said.

More information

The American Cancer Society can tell you more about colon cancer.

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