By Rachael Rettner
Colonoscopies could be made a bit more comfortable for people if they involved lying in a CT scanner, rather than being probed with an endoscope, and at the same time didn't require drinking upward of a gallon of laxative fluid beforehand — current requirements that most consider unpleasant.
A new type of "virtual colonoscopy" that uses CT scans to construct images of the colon, as well as to virtually "clean" the organ, was just as effective as a standard colonoscopy in finding colon polyps 1 centimeter or larger in size, a new study finds. Most polyps, or growths on the lining of the colon, are benign, but some can turn cancerous.
"The subtraction of the laxative can only make what's already an attractive test even more attractive," said Dr. Durado Brooks, director of prostate and colorectal cancer at the American Cancer Society, who was not involved with the study.
The discomfort of colonoscopies may deter some people from getting screened, said study researcher Dr. Michael Zalis, an associate professor of radiology at Massachusetts General Hospital.
If this laxative-free, CT scan type of virtual colonoscopy becomes an option for colon cancer screening, Zalis said, it could increase the number of people who get screened, and thus reduce the number of deaths from the disease.
The laxative-free method was not as effective as a standard colonoscopy in finding polyps smaller than 1 centimeter, but polyps of this size are less likely to cause cancer, according to the National Institutes of Health. The new findings must be confirmed by larger studies before the test is put into practice, Zalis said.
The study is will be published Tuesday (May 15) in the journal Annals of Internal Medicine.
No laxative required
Each year, there are about 120,000 new cases of colon cancer in the United States, and 50,000 people die from the disease,Zalis said.
Several methods are available to screen for colon cancer, including blood and fecal tests. But the "gold standard" is the colonoscopy, and the type most commonly performed is the optical colonoscopy, which uses a fiber optic tube with a light and camera to examine the internal surface of the colon. Another method, computed tomographic colonography (CTC), uses images produced by CT scans to indirectly view the colon. Both methods require patients to drink a laxative the day before their procedure.
More than 90 percent of colon cancer screening is done with colonoscopies or the blood tests, Brooks said.
In the new study, 604 people ages 50 to 80 who were eligible for a colonoscopy received the new test — a laxative-free CTC. Participants were required to eat a low-fiber diet for two days before the procedure, and to ingest small doses of a contrast agent that labeled their stool so that it was distinct from the colon on an X-ray. About five weeks later, the same patients were given an optical colonoscopy.
The laxative-free CTC correctly identified 91 percent of people with polyps 1 centimeter (10 millimeters) or larger. The results for the optical colonoscopy test were similar; it identified 95 percent of people with polyps of this size.
However, the colonoscopy was better at finding smaller polyps: it correctly identified 76 percent of people with polyps 0.6 centimeters or larger, while laxative-free CTC identified 59 percent of people with polyps of this size.
Three cases of colon cancer were diagnosed in the study. These cases were detected by both screening methods.
Participants said the laxative-free method was more comfortable and easier to prepare for than the colonoscopy. Sixty-two percent said the laxative-free method was their preferred method of screening.
Not a 'game changer'?
While laxative-free screening might increase the number of people who get colon cancer screening, "I don’t think it will be the big game changer that [the authors] suggest," said Dr. John Monson, chief of the division of colorectal surgery at the University of Rochester Medical Center, in New York, who was not involved in the study.
There are many reasons people do not get screened for colon cancer besides the requirement of a laxative, Monson said. For instance, some find other aspects of the test not agreeable, and others may be frightened to know the results, he said.
All virtual colonoscopies have a disadvantage in that, if polyps are found during the test, a follow-up colonoscopy is needed to remove them, Monson said. In addition, while polyps larger than 10 millimeters confer the greatest risk of colon cancer, most doctors do not feel comfortable leaving behind polyps that are 0.6 centimeters in size, Monson said.
CTC is currently considered an accepted method of screening by the American Cancer Society, but not by the U.S. Preventative Services Task Force.
The ACS recommends that people who get virtual colonoscopies be re-screened in five years; those who get optical colonoscopies are recommended to wait 10 years between tests.
Zalis said laxative-free CTC might first be offered to people who have only a moderate risk of colon cancer (those 50 and older without a family history of the disease, or other risk factors, such as inflammatory bowel disease). Some people may also be unable to have a colonoscopy, for instance, if they cannot be sedated for a medical reason.
While CTC uses X-rays, the dose is much lower than that required for a CT scan used to diagnose disease, Zalis said. A study published in 2005 published in the journal Gastroenterology concluded the cancer risks associated with exposure to radiation from CTC are small.
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