Radiation Exposure During Virtual Colonoscopy Doesn't Significantly Raise Cancer Risks

"It's good news that the radiation risk is low with CT colonography,but many practical issues need to be addressed before the test can berecommended to patients for routine colorectal cancer screening," saidAGA President David A. Peura, MD. "Evaluating issues of standardizationand accuracy of test results and addressing disparities in consistentand uniform training of professionals performing the test should be thefocus of future studies. In addition, the procedure still requires agreat amount of bowel preparation and causes discomfort--both issueslargely affect the current state of patient compliance in colorectalcancer screening."

Researchers from the Center for Radiological Research at ColumbiaUniversity Medical Center estimated the radiation dose to differentorgans from adult CT colonography scans. Dose-, organ- andgender-specific excess relative risks for cancer incidence in JapaneseA-bomb survivors were used as a basis to generate risk estimates forthe U.S. population. This study found the estimated lifetime risk ofcancer as a result of radiation from CT colonography in a 50-year-oldsubject is about 0.14 percent and 0.022 percent for a 70-year-oldpatient. The main organs found to be at risk for cancer are the colon,stomach and bladder.

"Our study shows that radiation risks associated with virtualcolonoscopy are relatively small--much smaller, for example, than forCT-based lung cancer screening," said David J. Brenner, PhD, lead studyauthor with the Columbia University Medical Center. "With the potentialfor low cancer risks and the use of non-cathartic bowel preparation,virtual colonoscopy is a very promising modality which couldpotentially increase patient compliance with current guidelines forcolorectal cancer screening."

A future trends report published by the AGA¹provided a review of clinical trials and quantitative mathematicalmodels to determine the potential role of CT colonography in colorectalcancer screening. Limitations of CT colonography included variation inresults of clinical trials and limited data on its use in routineclinical practice. Questions currently being addressed in clinicaloutcomes studies include:

• Is there a minimum polyp size detectable by CT colonography for which patients should be referred for polyp removal?
• What is the minimum-sized lesion by which CT colonography sensitivity will be judged?
• What polyp size, if any, would physicians and more importantly their patients, allow to remain in place and undergo surveillance rather than immediate removal?
• How will CT colonography screening followed by colonoscopy for patients with polyps impact patients' compliance and health-care costs?

Bowel preparation continues to be a large barrier topatient compliance for colorectal cancer screening. In most current CTcolonography protocols, patients must undergo rigorous bowel cleansingpreparation similar to that of traditional colonoscopy. However,significant progress is being made in the development of a minimalpreparation or "prep-less" CT colonography test -- which wouldpotentially have a major impact on patient compliance.

Guidelines of multiple agencies and professional societies underscorethe importance of screening for all individuals 50 years of age andolder. Currently, there are a number of tests that may be used toscreen for colorectal cancer, the second-leading cancer killer in theUnited States. Approved tests include barium enema, fecal occult bloodtest, flexible sigmoidoscopy and colonoscopy. Each screening option hasadvantages and disadvantages, and patients should consult theirphysician on the most appropriate test.

More information on colorectal cancer screening is available at www.gastro.org.

About the AGA

The American Gastroenterological Association (AGA) is dedicated to themission of advancing the science and practice of gastroenterology.Founded in 1897, the AGA is the oldest medical-specialty society in theUnited States. The AGA's 14,500 members include physicians andscientists who research, diagnose and treat disorders of thegastrointestinal tract and liver. On a monthly basis, the AGA publishestwo highly respected journals, Gastroenterology and Clinical Gastroenterology and Hepatology.The AGA's annual meeting is Digestive Disease Week, which is held eachMay and is the largest international gathering of physicians,researchers and academics in the fields of gastroenterology,hepatology, endoscopy and gastrointestinal surgery.

About Gastroenterology

Gastroenterology, the official journal of the AGA, is the mostprominent journal in the subspecialty and is in the top one percent ofindexed medical journals internationally. The journal publishesclinical and basic studies of all aspects of the digestive system,including the liver and pancreas, as well as nutrition. The journal isabstracted and indexed in Biological Abstracts, CABS, ChemicalAbstracts, Current Contents, Excerpta Medica, Index Medicus, NutritionAbstracts and Science Citation Index. For more information, visit www.gastrojournal.org.

¹ Van Dam J, Cotton P, Johnson CD, McFarland BG,Pineau BC, Provenzale D, Ransohoff D, Rex D, Rockey D and Wootton FT,III. AGA Future Trends Report: CT Colonography. Gastroenterology 2004; 127: 970-984.