Why Mammography CAD Matters

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Western Missouri Radiological Group for Encompass Medical Group is using the Kodak Carestream CAD for mammography system with film mammography studies.

Computer assisted detection for mammography first entered the scene in the late 1990s. Approval by the FDA with subsequent granting of increased reimbursement for the use of CAD by Medicare launched adoption of this technology into hospitals and imaging centers across North America. Many subsequent studies have proven its worth in increased detection rates of breast cancers at an earlier stage, many of which could otherwise be missed.  

CAD’s value, however, is now being challenged by some. The publication in the April 5th issue of the New England Journal of Medicine of a large, multi-center study that reported that the use of CAD reduced accuracy of mammographic interpretation sent shockwaves through women’s imaging centers and industry, and has sparked lively debate about the study’s results. “Influence of Computer-Aided Detection on Performance of Screening Mammography” by Fenton, et al has raised numerous questions about the use of CAD in mammography.

This study “linked data from surveys that were mailed to mammography facilities and affiliated radiologists to data on mammograms and cancer outcomes for women screened between 1999 and 2002.” It involved a total of 43 facilities across three states, all members of the Cancer Surveillance Consortium and compiled data from a total of 429,000 screening mammograms performed on 222,000 women between 1998 and 2002. The results suggested that within the seven institutions where CAD was implemented during the study period, not only did CAD not improve the detection of breast cancer; it resulted in a higher rate of false-positive mammogram results and increased the recall and biopsy rate. The study did, however, suggest that CAD could be helpful in finding ductal carcinoma in situ.

Not surprisingly, experienced mammographers who have used CAD for many years have questioned some of the study findings. Issues such as lack of CAD utilization experience in those radiologists who were using newly installed systems, tumor size at the point of detection, and the age of the women at time of diagnosis have been raised. Even the study authors acknowledge that since “computer-aided detection is used in the screening of millions of healthy women, larger studies are needed to judge more precisely whether benefits of routine use of computer-aided detection outweigh its harms.”

CAD finds smaller lesions

Judy C. Dean, MD, a radiologist in private practice in Santa Barbara, Calif., observes that this study spanned years that would necessarily mean all of the sites were using an older version of CAD because the seven institutions who provided CAD data had installed the equipment during the study period (the average amount of time the facilities had been using CAD was seven months). While those CAD applications were not inferior in quality, the newer versions of CAD, especially those that are used with FFDM systems, include refined algorithms.

When Dean’s practice first installed CAD in 2002, she preferred to read cases, make a decision as to whether or not to recall a patient, wrote that conclusion down, then applied the CAD marks to the image. Following that procedure, she then tracked the number of additional patients who were recalled due to the results provided by CAD as opposed to those who would have been recalled based on her initial interpretation.

“Recall rates are impacted the most when you first start using [CAD],” she notes. However, they found that recall rate with CAD decreased with experience. The recall rate in her practice doubled during the first two months of use, but then returned to a modest 9 percent above the pre-CAD rate. Dean cites another study published in Radiology in 2006 that revealed that women would prefer to be called back for more procedures if it might result in earlier detection of cancer.

More importantly, Dean found that in a prospective evaluation of CAD that they were detecting significantly smaller cancers. Invasive, non-palpable breast cancers detected with CAD had a mean size of 5 mm, compared with 10.5 mm for similar cancers detected without CAD, which she assesses to be a huge improvement since early detection improves outcome. While the Fenton study did not provide data about the size and stage of cancers detected, Dean considers that to be of utmost importance.  

The most significant issue in