Virtual colonoscopy has been touted as a noninvasive and safe way of screening for colon cancer, but a new study adds to a growing body of evidence that it's not yet ready to replace the standard colonoscopy.
During a standard colonoscopy, after the patient is sedated, a scope is inserted into his/ her colon. The physician can detect cancerous or precancerous lesions and remove them immediately.
With a virtual colonoscopy, the patient undergoes a CT scan that takes images of the colon. These are analyzed later, and if any lesions are found, they are removed during a traditional colonoscopy.
Before either procedure is performed, patients must fast, take laxatives and/or use enemas to clean the colon.
In this study, researchers analyzed a mathematical model comparing virtual colonoscopy with standard colonoscopy. They found that virtual colonoscopy was associated with more cancer deaths than standard colonoscopy.
There were 66 more deaths related to colon cancer per 100,000 patients who had virtual colonoscopy, compared with standard colonoscopy, says lead researcher Dr. Douglas Faigel, an associate professor of medicine at Oregon Health and Science University.
"It is up to the public to decide whether it is worth doing virtual colonoscopy, given the death rate," he says.
Weighing The Risks
"Virtual colonoscopy has risks," says Faigel. One of these risks is cancer caused by the radiation used during the virtual colonoscopy, he says. "The risk to an individual patient is rather low, but over 100,000 patients, you are going to see excess cancers," he says.
"In addition, if you have a virtual colonoscopy and you see polyps, you [still] have to have a regular colonoscopy with all of its risks."
Virtual colonoscopy also misses more cancerous and precancerous lesions than standard colonoscopy, Faigel says. "If you miss important lesions, then you are going to have more patients get colon cancer after a virtual colonoscopy than [after] a standard colonoscopy," he says.
Virtual colonoscopy is not safer or cheaper or more comfortable than regular colonoscopy, Faigel says. "I don't think virtual colonoscopy, as it is being done right now, really has a role," he adds. "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."
Virtual Colonoscopy Down, But Not Out
This study is a simulation, cautions Dr. Durado Brooks, director of colorectal cancer at the American Cancer Society. The risks associated with virtual colonoscopy seem a little high, he says. "Virtual colonoscopy is really in its infancy, and it is in a state of rapid evolution," Brooks notes.
But, he adds, the data n this study is from several years ago, and therefore, doesn't reflect virtual colonoscopy as it is done today. The amount of radiation used is getting lower and the accuracy is improving to near that of standard colonoscopy, he says. Although one study found that virtual and standard colonoscopy are equally accurate, these results have yet to be replicated, Brooks adds.
"Virtual colonoscopy is a work in progress," Brooks says.
Although virtual colonoscopy is not recommended as a screening tool for colon cancer by the American College of Radiology or other groups, Brooks believes that in the future 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 says.
Faigel believes that if the level of radiation was reduced and the accuracy of the procedure improved, then virtual colonoscopy would be comparable to standard colonoscopy.
"In addition, if you can get to a prep-less virtual colonoscopy, which might increase compliance, then maybe it might be beneficial," Faigel says.