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High tech tool against colon cancer


At this time of year, you might expect an invitation to a dance recital or a graduation, but Dr. Paul Keller’s friends and colleagues are hearing about something a bit less festive. He’s inviting them – “strongly urging” might be more accurate – to get their names on the list for a virtual colonoscopy.

It’s a procedure for discovering growths on the inside wall of the intestine, so Keller’s invitation sounds like one you wouldn’t mind losing on the way home. But finding those growths, called polyps, can prevent the development of colorectal cancer, the nation’s No. 2 cause of cancer death. This year in Iowa, the American Cancer Society expects 1,840 new colon cancer cases and 710 deaths from the disease. And when you compare the relative simplicity of virtual colonoscopy with the unpleasantness usually conjured up by the phrase “colorectal exam,” you might be even more inclined to take Keller’s advice.

Keller specializes in body imaging at the Iowa Radiology diagnostic center in the John Stoddard Cancer Center on the Iowa Methodist Medical Center campus. The key to the group’s virtual colonoscopy work is a $1.1 million CAT (computerized axial tomography) scan machine installed about a year ago. In addition to many other internal imaging tasks, the device produces the high-resolution X-ray images necessary for reliable colonoscopy results. “They’ve been talking about a procedure like this for quite some time,” said Keller. “But it wasn’t possible until the necessary technology was developed” to produce extremely detailed images.

The patient lies on a table and holds his or her breath for 20 seconds as the table slides through a big, doughnut-shaped structure called a gantry. X-ray devices inside the gantry record a sequence of images from all around the body at high speed, mapping the entire colon. To produce the most accurate results possible, patients go through this step twice, once lying on their back and again on their stomach. All of the information is collected in a matter of seconds and the appointment is finished.

“We just had a patient who had already undergone both optical colonoscopy and the barium enema procedure,” Keller said. “When this was over, she couldn’t believe that was it.”

Computer software turns the X-ray images into high-resolution graphics suitable for close study on a compute monitor. Keller, who received special training on this subject in a two-day session at the University of California at San Francisco, typically spends about 20 to 25 minutes examining the results. Customized software allows him to eye any spot in the colon from various angles or to “fly through” the colon, checking for suspicious-looking lumps as small as 4 millimeters (about one-sixth inch) in diameter.

Although the virtual colonoscopy procedure itself is not difficult for the patient, the preparations are not exactly material for a vacation brochure. Patients must follow a special low-residue diet for 24 to 48 hours beforehand, take laxative pills the night before the appointment and drink a modest amount of a substance containing barium.

Then, in the CAT scan room, technologists spend two or three minutes filling the patient’s colon with carbon dioxide gas to improve the accuracy of the results. “Most patients say they feel nothing,” said technologist Renee Newsom. “And, unlike air, carbon dioxide is absorbed by the body.” Then it’s time for the CAT machine. The entire office visit can be as short as 20 minutes, Newsom said.

A major drawback for most patients, however, is the cost of the procedure, which is $1,000 at Iowa Radiology. Most health insurance plans don’t cover it.

Keller predicts that public demand will lead insurance companies to add virtual colonoscopies to their coverage plans soon. “In six months to a year, I think we’ll see more companies paying for it,” he said.

He contends that the relative ease of this procedure will encourage more people to get screened, thereby benefiting the effort to reduce the incidence of colorectal cancer. “The American Society of Gastroenterology estimates that only about 30 percent of eligible people are being screened for colon cancer,” Keller said. “We’re getting phone calls from people in a number of Iowa towns because they know we do this procedure.” Keller recommends this approach for low-risk patients over 50, with risk determined by family history and lifestyle factors. He steers higher-risk people toward the colorectal screening methods with a longer track record.

Iowa Radiology began doing virtual colonoscopies about a month ago and has kept the schedule light to allow doctors and technologists to get comfortable with the process. Four patients received virtual colonoscopies at Iowa Radiology in a recent week, and the waiting list contains about 50 names—including Dr. Paul Keller, age 51.

A study published in the New England Journal of Medicine at the end of 2003 concluded that virtual colonoscopy is an accurate screening method for people at average risk of colorectal cancer. However, not everyone is sold on this diagnostic technique. The American Cancer Society reviewed the study’s data and came to the opposite conclusion. “The American Cancer Society concluded that there is insufficient evidence to recommend virtual colonoscopy for screening the population at average risk,” said local ACS spokeswoman Kerry Finnegan. “But the technology is maturing, and we believe it has the potential to become a useful screening tool.”   

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