Researchers at Duke University Medical Center believe they will be able to settle once and for all a long-running medical controversy -- what is the best way of detecting polyps in the colon? Is it the standard air contrast barium enema, the traditional colonoscopy or the newest high-tech option, the virtual colonoscopy?
Accurately detecting these polyps is important, researchers say, because if they are found early and removed, chances are extremely low that patients will develop colon cancer, the second leading cause of cancer death in the United States.
All three tests are designed to spot abnormalities in the mucosal lining of the colon, the final section of the large intestine. The most common colon abnormalities are benign growths called polyps, which can ultimately become malignant if left untreated.
Armed with an $8 million grant from the National Institute of Health's (NIH) National Cancer Institute, a team of researchers led by Duke's Dr. Don Rockey will compare the two time- tested detection methods with the new virtual colonoscopy, which uses spiral CT scanners to produce images of the colon. Computer software then reconstructs the images to provide three- dimensional views of the colon from the inside. "By the conclusion of this trial, we should be able to definitively answer the question of which method is the best at detecting polyps and other lesions in the colon," Rockey said. "We expect that the results of this trial which is the largest such trial funded by the NIH will form the scientific basis for setting national policy standards for imaging techniques in detecting colon cancer. While colon cancer is a leading cause of cancer death in the U.S., it is one that we have a very good chance to treat, if we catch it in time."
While the current trial is designed to find the most accurate method of detecting polyps, researchers also want to answer equally important questions about how each of the tests is viewed and tolerated by patients, as well as their cost-effectiveness.
The research team plans to enroll 3,800 patients over four years at hospitals at Duke and the University of California at San Francisco. Patients at Veterans Affairs Medical Centers (VAMC) in Durham and San Francisco also will be eligible.
In order to be admitted into the study, patients must have evidence of blood in their stools. These patients are at the highest risk for colon cancer, Rockey said, so it is recommended that anyone with blood in the stool receive a colon imaging study. While there are no age limitations to participate in the trial, Rockey expects that most participants will be between the ages of 50 and 70.
Over a week to 10-day period, participants will undergo all three of the tests. Although that prospect may seem daunting to some, Rockey said that patients should welcome the opportunity to receive such a comprehensive screening at no additional cost.
"If someone learns that they have blood in their stool and may be at higher risk for colon cancer, many will want every test possible," Rockey said. "Each individual test, if done alone, can miss potential cancers. However, it is extremely unlikely that a cancer will be missed in someone undergoing all three of these tests."
Each one of the approaches has its own benefits and limitations -- as measured by its accuracy, tolerance and cost -- and the researchers are confident that by the end of the trial they will be able to determine which test is the most appropriate for each individual situation.
In an air contrast barium enema (ACBE) procedure, a small volume of barium is introduced into the colon, which is then distended with air, coating the surface of the colon with a thin layer of this high-density element. The barium acts as a contrast agent, permitting an X-ray study to reveal any abnormalities along the colon. This approach is the least expensive, minimally invasive and very safe, according to Rockey, but it does not provide the clearest view of the colon.
For a colonoscopy, a flexible tube containing a light source and camera is inserted through the rectum and into the colon, allowing physicians to visually inspect, in color, the walls of the colon. The colonoscopy lets doctors actually see and identify any abnormalities, and, unlike ACBE, permits physicians to remove polyps during the same procedure. But, Rockey points out, colonoscopy is much more expensive, requires patients to be sedated and is invasive.
The third option, the virtual colonoscopy, has only been used for examining the colon during the past few years. According to Dr. Erik Paulson, a Duke radiologist and member of the research team, this latest development was made possible by advances in CT and computer workstation technology.
"The scanner's X-ray tube revolves around patients as they move through the scanner, capturing vast quantities of high resolution data very quickly," Paulson explained. "The imaging data is then shipped to computer workstations, where the images can be viewed from a variety of perspectives.
"We can view the colon from the inside out, from the outside in, or we can straighten it out to examine the walls from any perspective," Paulson continued. "There have been several studies that looked at small numbers of selected patients, and the virtual colonoscopy was shown to be a promising technique for detecting significant polyps. But what has been lacking is a large-scale study comparing it to the other modalities in a true screening population."
While the virtual colonoscopy takes only a number of minutes to perform, it does require that a tube be inserted into the rectum in order to distend the colon with air. It is also the most expensive approach, according to Rockey.
Each of the three approaches requires patients to prepare themselves 24 hours before the test by eating a clear liquid diet, and cleansing the colon through the use of laxatives, special diets or enemas. All three approaches require clean colons to obtain the best images.
The team of specialists for the trial are, from Duke, Dr. Wendy Davis, Dr. Dawn Provenzale, Hayden Bosworth, Dr. William Foster, Dr. Daniel Heller, Dr. Vincent Low and Linda Sanders. Team members from UCSF include Dr. Robert Halvorsen, Dr. Johannes Koch, Dr. Kenneth McQuaid and Dr. Judy Yee.
For more information about participating in the trial at Duke, contact Yvonne Ford at 919- 668-0731.