The efficacy of computed tomographic colonography (CTC), or virtual colonoscopy, might be a debatable topic for the medical community at large, but at the University of Wisconsin Medical School (Madison), the point is moot. The results of recent research convinced local HMOs that the procedure has enough benefit to be reimbursable.

The study, which used the latest CT technology and methods as well as highly trained physicians, found that “the use of a 3-D approach is an accurate screening method for the detection of colorectal neoplasia in asymptomatic average-risk adults and compares favorably with optical colonoscopy in terms of the detection of clinically relevant lesions.”1

Even so, Perry J. Pickhardt, MD, associate professor of radiology at the University of Wisconsin and lead author of the study, believes the decision to have a CTC procedure rather than a traditional colonoscopy should be left to the patient. “Both methods are acceptable, and both should be an option,” he says, noting the real point: “There are far too many people not getting screened.”

According to Pickhardt, the hallways between the radiology and gastroenterology departments at the University of Wisconsin have become two-way streets for patients. Patients whose CTC exams show polyps are sent to gastroenterology for follow-up; those with uncertain results in traditional colonoscopy are followed up in radiology.

In turn, the university has successfully dealt with many of the issues facing widespread acceptance of CTC: efficacy, responsibility, follow-up, and reimbursement.

Screening Saves Lives

According to the American Cancer Society (ACS of Atlanta), colorectal cancer is the third most common cancer in men and women. This year, the ACS expects just over 150,000 new cases, up slightly from 2002, when 148,300 new cases and 56,600 deaths were estimated.

Screening for colorectal cancer can help reduce related death-early diagnosis and treatment of colorectal cancer results in a survival rate of greater than 90%.2 Screening also can prevent the development of colon cancer by identifying and removing adenomatous polyps, from which these cancers often develop.2

The ACS recommends one of five screening schedules for persons over the age of 50:

  1. An annual fecal occult blood (stool blood) test;
  2. Flexible sigmoidoscopy every 5 years;
  3. An annual fecal occult blood test, plus flexible sigmoidoscopy every 5 years;
  4. Double-contrast barium enema every 5 years; or
  5. A colonoscopy every 10 years.

For this group, Medicare will cover annual fecal occult blood tests, flexible sigmoidoscopy every 4 years, and double-contrast barium enema as an alternative if the physician deems it of equal or greater value. After strong advocacy efforts by the ACS, Medicare expanded its coverage of colonoscopy in 2001 for colorectal cancer screening to include the test once every 10 years for beneficiaries age 50 and over with an average risk.3 It does not yet offer coverage for CTC.

Despite the life-saving advantages of and the reimbursement for screening, however, the methods are vastly underused. From 1987-2000, the percentage of US adults aged 50 and older who were screened grew only 12%, from 27% to 39%, based on National Health Interview Survey data.2

Technology and Technique Influence Efficacy

Supporters of CTC believe that the procedure could help to achieve ACS’ 2015 goal of screening for 75% of adults over the age of 50. CTC is substantially less invasive than traditional colonoscopy, requiring no sedation and, therefore, no recovery time, making the procedure more attractive to patients. The risk of perforation or tearing of the colon is also removed.

The preparation, or bowel cleansing, is nearly identical to that of conventional colonoscopy, according to Matthew Barish, MD, director of the 3-D and image processing center at Brigham and Women’s Hospital (Boston); assistant professor of radiology at Harvard Medical School (Boston); director of the International Symposia on Virtual Colonoscopy; and chief medical adviser for Barco (Boston), which recently acquired Voxar Inc. In the future, he expects this phase to become less demanding.

First seen 10 years ago, the technique has improved with technology and, as a result, so has its efficacy-one of the major concerns of those questioning its value. The American Gastroenterological Association (AGA of Bethesda, Md) made the following conclusion in its report:

In summary, available studies comparing CTC and colonoscopy have shown a wide variation in results. Reasons for variability reported in studies include variation in the techniques used to prepare/cleanse patients and perform the studies, differences in CTC technology (both hardware and software), and variability in the manner in which CTCs have been read. In the two larger studies reported to date, the sensitivities of lesions greater than 1 cm were 54% and 92%, respectively, reflecting many of these issues. Because the best results were obtained in some of the most recent studies using the latest techniques, it would be problematic to consider the results of the earlier and later studies equivalent.4

Allyson Mortati, global product manager of virtual colonoscopy at E-Z-EM Inc (Westbury, NY), echoes this difference in discussing two popular studies: the Pickhardt study, published in December 2003, and another led by Peter B. Cotton, MD, director of the digestive disease center at the Medical University of South Carolina (Charleston), which was published in April 2004.

“The Pickhardt study used the latest technology and expert readers. Cotton used older technology and less-expert readers. Pickhardt’s results were positive, and Cotton’s negative,” Mortati explains.

But Cotton had a different goal than Pickhardt. One of his aims was to mimic the conditions likely to be found in community practice. The study was conducted in nine hospitals by radiologists required to have performed at least 10 similar procedures.5

The results showed the sensitivity of CTC to be 39% for lesions at least 6 mm in diameter and 55% for lesions with a diameter of at least 10 mm.6 These results were significantly lower than those for conventional colonoscopy, with sensitivities of 99% and 100%, respectively.6 Cotton concluded that “regular radiologists” could not reproduce the results of other studies, such as Pickhardt’s.7

Pickhardt does not find these results surprising, noting the importance of realizing that the specific technique and software used are relevant. “We’ve seen in multiple studies that outdated techniques and methods will produce disappointing results,” he says.

In his study, patients of average risk underwent the standard 24-hour colonic preparation in addition to consuming materials for stool tagging and opacification of luminal fluid.1 A four- or eight-channel CT scanner was employed, and a 3-D view was used for initial detection of polyps.4 Results were interpreted by board-certified radiologists who had received training that involved reading a minimum of 25 virtual colonoscopic studies.

Pickhardt found the sensitivity of CTC for adenomatous polyps to be 93.8% for polyps at least 10 mm in diameter, 93.9% for polyps at least 8 mm in diameter, and 88.7% for those at least 6 mm in diameter.1 The sensitivity of optical colonoscopy was 87.5%, 91.5%, and 92.3%, respectively.1

Well-Trained Physicians Improve Results

Pickhardt attributes the high efficacy of his results to the use of 3-D evaluation. “Many physicians are still using the 2-D axial view, which is a very difficult search pattern. Rather than searching in two dimensions and switching to three to examine a polyp, the procedure should be reversed. The initial exam should be done in 3-D and a polyp confirmed in 2-D,” he says.

As illustrated by the contrast in the Cotton and Pickhardt studies, a physician with the appropriate training is likely to be more accurate than one untrained in the specialty. The AGA notes in its report that “reader training is critical and currently a limiting factor in CTC”.8 The colon committee of the American College of Radiology (ACR of Reston, Va) is developing CTC standards for protocols and reporting of findings.8

Currently, training can be obtained at educational institutions, such as the University of California San Francisco (UCSF) and Harvard University, as well as vendors, such as E-Z-EM. Events-like the International Symposium on Virtual Colonoscopy, held every October in Boston-also offer opportunity for education.

“It’s not enough to see one, do one,” says E-Z-EM’s Mortati. “Physicians need quite a bit of practice. It’s generally considered best to use studies that have been done already.”

Judy Yee, MD, vice chair of radiology at UCSF and chief of radiology at the San Francisco VA Medical Center, believes radiologists are better trained to interpret CTC exams.
Judy Yee, MD, vice chair of radiology at UCSF and chief of radiology at the San Francisco VA Medical Center, believes radiologists are better trained to interpret CTC exams.

Because of the need for specialized training, interpretation of virtual colonoscopy exams has remained primarily within the domain of radiology. “Thus far, the exams are being performed and interpreted most frequently by radiologists. Some gastroenterologists can read the 3-D images, which are similar to an endometrial fly through, but they are not trained in 2-D,” says Judy Yee, MD, vice chair of radiology at UCSF and chief of radiology at the San Francisco VA Medical Center.

Boston’s Barish notes that radiologists also are required to read the exams because CTC allows visualization of the other abdominal organs. The AGA states that the detection of extracolonic abnormalities is an important issue for CTC.4 One study has found that low-dose CTC detected highly significant extracolonic findings, though only a small proportion of patients required further diagnostic testing.8

Picking Polyps

Follow-up care is not required in a large percentage of cases. In the Pickhardt study, the prevalence of adenomatous polyps 10 mm or larger in diameter was 3.9%; for those 8 mm or larger in diameter, it was 6.7%; and for those 6 mm or larger, prevalence was 13.6%. Generally, only 1%-2% of colonoscopy patients have large polyps detected; small ones can be found in 30% or more of screened patients.9

The medical community is questioning whether there is a minimum polyp size for which patients should be referred for endoscopic polypectomy.4 Physicians also are asking if there is a minimum-size lesion by which CTC sensitivity should be assessed and what that size is.4 Some think there is a minimum size. Barish believes that smaller lesions pose little risk to the patient. “Their removal could expose the patient to greater risk of complications from biopsy,” he says.

The AGA Future Trends Report4 notes, “There is general agreement that CTC should detect polyps greater than or equal to 1 cm and that patients with polyps in this size range should be referred for polypectomy. An early study of polyps detected by barium enema examination found that 1% of polyps 1 cm or larger converted to clinically evident cancer per year.” The report also concluded that polyps under 5 mm “do not appear to be a compelling reason for colonoscopy and polypectomy.” The most controversial are those between 5 and 10 mm, though general agreement is that polyps of this size are unlikely to be advanced.

The report also questions the influence of the shape of the polyp, sensile or flat; however, little research has been done on this topic, and definitive quantitative data does not exist.

Care Is a Two-Way Street

Whether sensile, flat, large, or small, if a polyp is deemed removable, one of the major concerns of practitioners is follow-up care. When a polyp is discovered in traditional colonoscopy, it is removed immediately. When one is discovered during a CTC exam, the patient is referred to gastroenterology for its removal. Depending upon the relationship between radiology and gastroenterology, follow up could occur immediately or be scheduled for a later date.

The ideal situation is immediate removal, and many facilities, such as the University of Wisconsin, are able to manage this goal. “We have a tight center so that the patient need undergo only one prep,” Pickhardt says. Patients are just as likely to come over from gastroenterology. When a traditional colonoscopy is indeterminate, a CTC often is recommended.

Doctors need not be territorial. “Only 20% of patients at best undergo a traditional colonoscopy, yet millions turn 50 each year. The patient population is large enough that the choice can be theirs,” Pickhardt says.

Yee adds that the shortage of gastroenterologists can be an additional benefit for CTC. “We can advocate virtual colonoscopy as a way to reduce the workload of gastroenterologists,” she says.

Multidisciplinary collaboration will be key to the procedure’s successful implementation into clinical care. The AGA expects CTC to have a significant impact on the practice of gastroenterology, stating that variability in results will be overcome, improvements in technology and software will continue rapidly, reader experience will improve, and bowel preparation will be minimized, at which point, the debatable issues will be moot.

Renee DiIulio is a contributing writer for Medical Imaging.

References

  1. Pickhardt PJ, Choi JR, Hwang I, Butler JA, Puckett ML, Hildebrandt HA, et al. Computed tomographic virtual colonoscopy to screen for colorectal neoplasia in asymptomatic adults. N Engl J Med. 2003; 349(23):2191-2200.
  2. American Cancer Society’s Statistics page. Cancer prevention and early detection: Facts and figures 2004. Available at: http://www.cancer.org/downloads/STT/CPED2004PWSecured.pdf. Accessed October 12, 2004.
  3. American Cancer Society’s ACS News Center. Medicare expands coverage of colonoscopy screenings. July 6, 2001. Available at: http://www.cancer.org/docroot/NWS/content/NWS_1_1x
    _Medicare_Expands_Coverage_of_Colonoscopy_Screenings.asp
    . Accessed October 12, 2004.
  4. Van Dam J, Cotton P, Johnson CD, McFarland BG, Pineau BC, Provenzale D, et al. AGA future trends report: CT colonography. Gastroenterology. 2004; 127(3):970-984.
  5. American Cancer Society’s ACS News Center. Virtual colonoscopy not ready for routine use. April 19, 2004. Available at: http://www.cancer.org/docroot/NWS/content/NWS_1_1x
    _Virtual_Colonoscopy_Not_Ready_for_Routine_Use.asp
    . Accessed October 12, 2004.
  6. Cotton PB, Durkalski VL, Pineau BC, Palesch YY, Mauldin PD, Hoffman B, et al. Computed tomographic colonography (virtual colonoscopy): a multicenter comparison with standard colonoscopy for detection of colorectal neoplasia. JAMA. 2004; 291(14):1713-1719.
  7. Reinberg, S. Colon cancer test disappoints. Healthfinder. Available at: http://www.healthfinder.gov/news/newsstory.asp?docid=518355. Accessed October 12, 2004.
  8. Rajapaksa RC, Macari M, Bini EJ. Prevalence and impact of extracolonic findings in patients undergoing CT colonography. J Clin Gastroenterol. 2004; 38(9):767-771.
  9. Williamson D. New virtual colonoscopy study disappoints, UNC physician: improve technique, training. UNC News Services. April 13, 2004. Available at: http://www.unc.edu/news/archives/apr04/ransho041304.html. Accessed October 12, 2004.