CT colonography stands at the crossroads between widespread adoption and not-yet-ready for prime time. Clinicians that use the technology and vendors that offer both the hardware and/or software components agree that the technology is an attractive alternative to optical colonoscopy that looks to spur increases in screening rates for colorectal cancer. But hurdles such as reimbursement, radiologist productivity in reading exams and proper bowel prep need to overcome first.
Nearly 150,000 Americans are diagnosed with colorectal cancer each year, making it the third most frequent cancer in the United States and the second most common cause of cancer deaths. While colorectal cancer has the highest mortality rate of all cancers, it can also be prevented if detected and treated early.
The American College of Radiology recommends that all 74 million Americans over the age of 50 be screened annually for colon cancer as well as younger, at-risk individuals with a strong family history. Early screening can detect and identify polyps, the most common precursor of cancer. Despite the advantages, the majority of the population avoids colorectal screening for its unpleasantness. The ACR estimates that only 10 to 12 million Americans are screened each year.
"Only 30 percent of the population that should get screened do," says Bob Beckett, global product manager, diagnostic oncology, GE Healthcare Technologies. "The reason for that is because [optical colonoscopy] is uncomfortable and invasive." For years, optical colonoscopy has been the gold standard for colorectal cancer screening at the price of being an undesirable procedure patients are reluctant to undergo.
An alternative diagnostic imaging procedure to optical colonoscopy that is gaining in clinical confidence is multislice computed tomography colonography (CTC). CTC is the process of combining multislice CT images and advanced visualization software to allow physicians to view, manipulate and examine the interior of the colon and detect polyps or tumors.
For patients, CTC is a quick, low-dose procedure that is non-invasive and does not require sedation or anesthesia. Bowel prep, however, is still necessary. It also eliminates the physical discomfort of conventional colonoscopy and associated risks, such as bleeding and perforation of the colon wall.
GETTING THE WORD OUT
Of late, the push for CTC as a way to reduce the incidence of colorectal cancer has been receiving more press and interest. Recent studies have demonstrated to both the medical community and patient population that CTC is an accurate method for the early detection of colorectal polyps. A 2003 study in the New England Journal of Medicine concluded that CTC is just as effective, easier and more convenient than optical colonoscopy. The department of Defense study (of 1,233 asymptomatic patients at low risk for colorectal polyps) found that virtual colonoscopy's sensitivity was 88.7 percent for polyps 6mm and larger, 93.9 percent for polyps 8mm and larger and 93.8 percent for lesions 10mm and larger, compared with slightly lower percentages for conventional colonoscopy of 92.3 percent, 91.5 percent and 87.5 percent, respectively. The study led to the Food and Drug Administration approval of Viatronix Inc.'s V3D Colon visualization software.
But adoption is not yet widespread. "CT colonography is a pretty new technique," says Haw Loke-Gie, clinical marketing manager for Siemens Medical Solutions' CT division. "There is not much awareness in the general community in terms of the patient, referring physicians and radiologists. I think that it requires more general education and training to make people more and more aware of the technique."
Siemens got on the CTC ticket in July 2003 when it released syngo Colonography. The application is available on Siemens' Wizard dedicated CT console, as well as its Leonardo multimodality standalone workstation.
Vendors and clinicians agree that 4-slice CT scanners and above is suitable to perform CTC. Increasing the slices count equates to faster acquisition times and higher resolution images. While faster scanning times improves the overall patient experience, it does not reduce the reading time for physicians.
"With conventional methods, the patient needs to be premedicated and sedated," explains Haw. "If the physician wants to do a full colonoscopy, it takes 30 to 45 minutes. A sigmoidoscopy takes about 20 minutes and the physician is only examining the lower colon. CTC requires