Continuing Improvements for Computer-Aided Detection in Screening Mammography
Heather Lindsey · Oncology Times · 2004
NEW YORK CITY—A computer-aided detection (CAD) system can significantly increase the rate of breast cancer detection, according to new research (Radiology 2004;232:578–584) discussed at a media briefing here on women's breast health sponsored by the Radiological Society of North America. “CAD can increase our detection rate of cancer early—a year or earlier—before we are currently diagnosing it on screening mammography,” said the study's lead author, Stamatia Destounis, MD, Clinical Assistant Professor in the Department of Radiology at University of Rochester (NY) and a staff radiologist at the Elizabeth Wende Breast Center there. Dr. Destounis and her colleagues reviewed cases of 519 patients with proven breast cancer. Prior screening mammograms were available for 318 patients and yielded a total of 98 false-negatives. Three out of five reviewers identified 52 actionable cancers that in retrospect appeared as visible abnormalities on prior screening mammograms but had been missed by two breast specialists conducting a non-blinded, double-read. Patricia Miller, MD, Assistant Director of Beaumont Hospital's Digital Breast Diagnostic Center in Royal Oak, Michigan, noted that because of time constraints, very few practices actually conduct physician double-reads. Dr. Destounis and her colleagues then used CAD (Image Checker V2.2 of R2 Technology of Sunnyvale, CA) to scan and analyze the false-negative mammograms. CAD correctly marked 37 (71%) of the 52 visible cancers missed during the double-read. Overall, the false-negative rate before CAD analysis was 13%, and the overall rate after CAD analysis was 19%. Not Perfect Of 218 CAD system marks, only 75 designated cancers. “CAD is not perfect,” explained Dr. Destounis, who is principal investigator for several CAD projects. “It marks a lot of things that turn out to be benign.”FigureCAD software needs continued improvement, Dr. Miller said, so that it doesn't highlight benign growths. For example, current software detects calcified blood vessels because calcifications look irregular. Another team of researchers at The Elizabeth Wende Breast Center recently finalized data from a prospective study of 18,586 screening mammograms, comparing the accuracy of one radiologist using CAD with two radiologists doing a blinded, double-read, Dr. Destounis noted. That study found that CAD reduced the overall false-negative rate by 5%, with the potential for an additional reduction of 16% if all the marked cancers had been acted upon. “In order for us to get better we have to find some way to have more confidence in the computer and listen to the correct marks,” she said. Other Benefits of CAD Despite the potential for false-positive readings with CAD, the technology does offer a number of benefits in addition to reducing the false-negative rate associated with physician readings. “We certainly have an increasing shortage of people willing to read mammograms, which makes double reading nearly impossible,” said Kathryn Evers, MD, Director of Mammography at Fox Chase Cancer Center. Under these circumstances it's good to have CAD working as a second set of eyes, she explained. Another benefit of CAD is that it doesn't get tired or distracted, said Dr. Evers, adding that researchers are continually improving the product. New CAD systems result in fewer false positives than a number of years ago. However, researchers have yet to gain a good handle on the false negative rate using this technology, she said.Figure: Stamatia Destounis, MD: “CAD can increase our detection rate of cancer early—a year or earlier—before we are currently diagnosing it on screening mammography….CAD is not perfect. It marks a lot of things that turn out to be benign….In order for us to get better we have to find some way to have more confidence in the computer and listen to the correct marks.”CAD is definitely the cheaper and faster option to doing physician double-reads, Dr. Miller said. “The initial cost is something to think about, but it's cheaper in the long run. I like CAD, especially in a busy practice, where you are reading hundreds of mammograms.” For expert readers who see thousands of mammograms a year, using CAD may not be as beneficial as it would be for practitioners in a general practice who don't have as much expertise. The New Standard? Whether or not CAD should be a standard remains to be seen, Dr. Miller said. For expert readers who see thousands of mammograms a year, using CAD may not be as beneficial as it would be for practitioners in a general practice who don't have as much expertise. “In general practice CAD may be very useful,” said Dr. Miller, adding that it offers a little bit of increased sensitivity for people who aren't expert readers.