Patients weighing the merits of colon cancer screening tests should stick with conventional colonoscopies at least for now rather than "virtual" procedures, according to research published in Wednesday's Journal of the American Medical Association.
Research has shown that colonoscopies, in which doctors use lighted scopes inserted into the rectum to find and remove polyps, can prevent cancer.
But patients hoping to avoid an invasive conventional procedure have been interested in the so-called "virtual colonoscopy," which uses computerized scans instead of scopes to produce 3-D images of the colon.
In December, a study published in The New England Journal of Medicine found that virtual colonoscopies were just as good as conventional ones. Radiologists who performed the screenings used state-of-the-art technology.
Wednesday's study, however, suggests that while the virtual screenings are promising, they are not yet reliable.
In a study of 600 patients at nine medical centers in the United States and England, researchers found that virtual colonoscopies found only 39 percent to 55 percent of precancerous lesions detected by the conventional test.
Researchers said they were surprised and disappointed by the results from the virtual screenings.
"I certainly wouldn't recommend it now," said Peter Cotton, director of the digestive disease center at the Medical University of South Carolina in Charleston. "This is a bucket of cold water to say, 'Let's back off a minute.' "
But Perry Pickhardt, who co-wrote the December study, said Cotton's research is outdated. Doctors can be expected to obtain poor results if they use older equipment and techniques and radiologists lacking experience, said Pickhardt, associate professor of radiology at the University of Wisconsin Medical Center.
The two studies show the difference between colonoscopies performed under ideal circumstances and those done in the real world, said David Ransohoff, a medicine and epidemiology professor at the University of North Carolina-Chapel Hill. In an editorial that accompanied Cotton's study, Ransohoff noted that virtual colonoscopies can create a dilemma for patients with small lesions: Should they undergo a second colonoscopy to remove the growths or wait and see if the polyps get bigger?
In the future, researchers hope to develop technology that could permit patients to undergo a "prepless" colonoscopy without taking laxatives to empty the bowels, Ransohoff said.
Pickhardt said that doctors need to set guidelines to ensure that patients get high-quality virtual screenings.
"For the next year or two, you just won't know what you are getting, unless you are near a well-established academic center or a very good private practice center," Pickhardt said. "People might be better off with regular colonoscopies if they can't get to a really good radiologist. But it's better to get either test than nothing."