McFarland plots course toward acceptance of CT colonography

December 4, 2008

In the aftermath of Medicare’s less than encouraging evaluation of virtual CT colonography for colorectal cancer screening, Dr. Elizabeth McFarland used the RSNA’s Annual Oration in Diagnostic Radiology to identify past achievements and ongoing initiatives she believes will lead to the modality’s acceptance.

In the aftermath of Medicare's less than encouraging evaluation of virtual CT colonography for colorectal cancer screening, Dr. Elizabeth McFarland used the RSNA's Annual Oration in Diagnostic Radiology to identify past achievements and ongoing initiatives she believes will lead to the modality's acceptance.

CT colonography was given a mixed reception at a Nov. 19 hearing before the influential Medicare Evidence Development & Coverage Advisory Committee. The MedCAC warmed to cost data indicating that CT colonography is less expensive than invasive colonoscopy without polypectomy, but the committee balked at endorsing its clinical merits because colonography had been recently rated as insufficient by the U.S. Preventive Health Task Force. Concerns about extracolonic findings and radiation exposure also arose during the hearing.

The task force's negative review contradicted a new American Cancer Society guideline, issued in September. It determined that CTC is comparable to optical colonoscopy as a screening exam for the detection of cancer and polyps of significant size. It concluded that enough data have accumulated to consider CTC an acceptable alternative to optical colonoscopy for colorectal cancer screening.

The ACS's willingness to wait for a confidential briefing on the results of a major American College of Radiology Imaging Network trial on colonography partially explains the differences in findings, McFarland said. The ACS evaluation was based on a multidisciplinary effort between the society and a task force composed of members of the three gastrointestinal medicine societies and the ACR.

The U.S. Preventive Services Task Force took a very different approach, McFarland said. It used a targeted symptomatic review looking at benefits and harm. Its analytic decision model compared the expected health outcomes and resource requirements of available screening modalities over time.

It concluded that three tests proved acceptable: fecal occult testing, flexible sigmoidoscopy, and colonoscopy. But CT colonography was scored as insufficient, based largely on the premise that the potential harm from radiation exposure and extracolonic findings could outweigh the benefits.

"This is a little bit neutralizing," McFarland said.

The MedCAC opinion increases the likelihood that the Centers for Medicare and Medicaid Services will mandate a "coverage with evidence development" requirement if it decides to grant Medicare coverage for colonography. CMS's decision is expected in February 2009.

Yet McFarland believes that the cohesive group of radiologists who first developed colonography will eventually win out.

"The community of CT colonography has been like a family … It revitalizes energy. It focuses direction. It gives us purpose. It is the culture of the effort that will motivate the future," she said.

She challenged her colleagues to address issues that still stand in the way of CTC's acceptance.

In terms of radiation exposure, there is a one-in-1000 risk of developing cancer from a single CT colonoscopy exam, based on linear, no-threshold modeling.

"But we know the counterpoints," she said. "Atomic bomb survivors (whose life experiences were used to calculate the estimates) were along all age groups, and the rates of induced cancer markedly drop within the screening range in the fifth decade of life and beyond."

CT colonography exposes a patient to 5 to 7 mSv, or slightly more than the expected normal environmental radiation exposure an adult American accumulates during a year, she said.

Extracolonic findings bring advantages and disadvantages, she said. A constellation of studies involving nearly 7600 patients found that extracolonic findings range from 5% to 15%. The ACRIN report was responsible for the upper-range 15%. Those results are still under analysis and included findings that were already known and did not lead to additional testing. The cost of the additional workups range from $25 to $34 per CT scan, she said.

Beyond the questions of safety and efficacy, the community needs to reach out to educate the general public and legislators about the benefits of CT colonography screening, McFarland said.

"Political involvement is everything at this point in the game," she said.

McFarland concluded by showing film clips contrasting the climax of The Perfect Storm, in which a fishing boat is overwhelmed by a gigantic storm in the Atlantic Ocean, and the end of Chariots of Fire, in which a runner remains true to his religious beliefs and still wins an Olympic gold medal.

"Do we become overwhelmed by the waves of obstacles, remain rigidly on a certain path, and not let go of our precious cargo?" she said. "Or do we run the race and remain true to our principles?"

The answers can be found in the power of the CT colonography imaging technology and the convictions held by the people who developed that technology, she said.