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."
The Times article quotes Dr. Julian Nicholas, a gastroenterologist who was contracted by the FDA, as saying that approving an application for virtual colonoscopy could "expose a number of Americans to a risk of radiation that is unwarranted and may lead to instances of solid organ abdominal cancer."
Adding to the concerns about radiation was a study late last year in the Annals of Internal Medicine that there was no consistent level of radiation received for patients having angiograms. It said some received up to 22 times the radiation exposure that other patients received, simply because of the level of radiation chosen by the lab technician.
But some physicians say recent literature has focused too much on the risk of radiation, comparing doses of radiation from imaging to that received from victims certain distances from World War II bombings.
Dr. Michael Macari, an associate professor of radiology at the New York University School of Medicine, said that the data is only "extrapolated… [bombing victims had] much greater radiation received than with conventional diagnostic radiation studies."
"With virtual colonoscopy," Macari said, "the low amount of radiation that one receives is similar to background radiation that one receives living in New York City for a year."
While virtual colonoscopy has advantages, some physicians say the benefits will be outweighed by what virtual colonoscopy doesn't find.
"It is less expensive and less uncomfortable and less hassle for the patient -- and many will have colon cancer missed because of it," said Dr. Richard Honaker, senior physician and CEO of Family Medicine Associates of Texas, Inc.
Others have pointed to the fact that polyps found on a virtual colonoscopy will require a colonoscopy anyway in order to remove them.
"If a lesion is found, the patient still needs a 'real' colonoscopy to remove/biopsy the lesion," said Dr. Randy Wexler, assistant professor of clinical family medicine at The Ohio State University. "This is another example of technology not necessarily improving anything."
President Obama had a virtual colonoscopy as part of his physical in February, seemingly a vote in its favor. But Dr. Richard Besser, ABC News' senior health and medical editor, said the president was in a unique situation: undergoing anesthesia for a traditional colonoscopy would have required a transfer of powers to Vice President Biden.
But with doctors deeply divided, Besser cautioned against make a screening decision on one's own. He said patients should consider their own situation.
"I want people to realize, if you have a CT scan planned right now, don't cancel it," he said. "Talk to your doctor. Find out why you're having that done. And make sure that the benefits of that scan really outweigh the risks."