Scientists at the Food and Drug Administration say their concerns over the radiation exposure from virtual colonoscopies were ignored by the agency.
In advance of a meeting today on limiting unnecessary patient exposure to radiation, scientists who worked at the FDA told the New York Times that their concerns about radiation from the CT scans used in a virtual colonoscopy were largely brushed off. Manufacturers have been pushing for the approval of the devices for colon cancer screening.
It is the most recent case of public disagreement among doctors over the benefits of virtual colonoscopies. Observers have pointed out that radiologists, who typically promote the benefits of virtual colonoscopies, have an interest in their use. Gastroenterologists, who administer traditional colonoscopies, tend to point out the flaws in virtual colonoscopies.
Conventional colonoscopy is performed with a long, flexible tube, inserted in a patient's colon. A doctor looks for evidence of cancer through optics in the tube as it is carefully snaked up the sedated patient's large intestine.
Virtual colonoscopy abandons that hardware in favor of a CT scan -- short for computed tomography -- of the patient's abdomen.
Doctors in favor of virtual colonoscopy say it eliminates the chance of perforated bowel that comes with traditional colonoscopies, as well as the risks that come with giving a patient anesthesia. They say more patients are likely to be screened for colon cancer, since a CT scan is less invasive than a traditional colonoscopy.
Opponents say virtual colonoscopies expose patients to radiation -- and if a polyp is found, a second surgical procedure must be done to remove it. With a traditional colonoscopy, the polyps can be removed at the same time as the colon examination. They also say incidental findings of the virtual procedure could lead to extra, possibly unnecessary tests.
The U.S. Preventive Services Task Force does not recommend the use of virtual colonoscopies, but other professional organizations do. The American Cancer Society and the American College of Radiology endorse the use of CT scans for this procedure, while the American College of Gastroenterology supports direct visual colonoscopy.
Doctors also remain divided over the issue, and that has led to some trouble when advising patients on the screening process.
"Virtual colonoscopy is a good option for a select group of patients that are not good candidates for the sedation of regular colonoscopy, that is, older or high-risk patients," said Dr. Martin Makary, a cancer surgeon and associate professor of public health at the Johns Hopkins University School of Medicine. "I advise younger patients not to get in the routine of having a CT scan every five years for the rest of their lifetime -- that's a lot of radiation which can be avoided.
"It's hard to study the 50-year downstream effects of things like modern CT scan radiation doses, but some research is now emerging that it's not dangerous, but it's not totally safe either. There are rare, radiation-induced cancers, like thyroid cancer and lymphoma, which are more common with certain exposures to radiation."