Radiologist Who Read More Diagnostic Mammograms Do It Better
Practice makes perfect or in the case of radiologists who interpret mammograms, the more diagnostic mammograms read increased the ability to do better at determining which suspicious breast lesions are cancer, according to a new report published online today (February 22, 2011) and in print in the April issue of Radiology.
Diana S.M. Buist, Ph.D., M.P.H., senior investigator at the Group Health Research Institute in Seattle and colleagues examined various measures of interpretive volume in relation to screening performance for 120 radiologists who interpreted 783,965 screening mammograms between 2002 and 2006.
The study included a review of data from six Breast Cancer Surveillance Consortium mammography registries in California, North Carolina, New Hampshire, Vermont, Washington and New Mexico.
Volume was measured in four ways: the number of screening and diagnostic mammograms read by a radiologist annually—both separately and in combination—and the ratio of screening to total (diagnostic plus screening) mammograms. Screening performance was measured by sensitivity (the ability to detect all cancers present) and false-positive and cancer detection rates.
The results showed that performance varied not only by the number of exams interpreted, but also by the ratio of screening to total (diagnostic plus screening) mammograms.
Because the study found that radiologists with higher annual interpretive volumes had lower false-positive rates—while maintaining sensitivity rates similar to their lower-volume colleagues—the researchers simulated the effect of increasing the minimum interpretive volume required of radiologists practicing in the U.S., which is currently 960 mammograms every two years.
"Contrary to our expectations, we observed no clear association between volume and sensitivity," said the study's lead author, Diana S.M. Buist, Ph.D., M.P.H., senior investigator at the Group Health Research Institute in Seattle. "We did, however, find that radiologists with higher interpretive volume had significantly lower false-positive rates and recalled fewer women per cancer detected."
"We also found that radiologists were more accurate at interpreting mammograms if they also interpreted some diagnostic mammograms." Dr. Buist said. Diagnostic mammograms evaluate breast symptoms or abnormalities seen on a prior screening mammogram.
The cancer-detection rate was highest when at least one in five of the mammograms that a radiologist read a diagnostic, not screening, mammogram—instead of their focusing more exclusively on reading screening mammograms.
Based on 34 million women aged 40-79 receiving screening mammograms each year, the researchers estimated that increasing the annual minimum total volume requirement to 1,000 would result in 43,629 fewer women being recalled. The estimated cost associated with false-positive results would be reduced to $21.8 million.
"Our analysis demonstrated that screening interpretive performance is unlikely to be affected by volume alone, but rather by a balance in the interpreted exam composition," Dr. Buist said. "The data suggest that radiologists who interpret screening mammograms should spend at least a portion of their time interpreting diagnostic mammograms, because radiologists who interpreted very few diagnostic mammograms had worse performance, even if they read a high volume of screening mammograms."
On average, for every cancer detected, 22.3 women were called back for more testing.
This report's findings have policy implications. The U.S. Food and Drug Administration (FDA) requires radiologists who interpret mammograms to read only 960 mammograms in two years, with no requirement about the type of mammograms they read (screening or diagnostic). In Europe and Canada, where volume requirements are 5 times higher, screening mammography programs have lower false-positive rates—but similar cancer-detection rates—than the United States.
Dr. Buist added: "Based on these data, it would be beneficial if U.S. volume requirements could be increased to 1,000 or 1,500 screening mammograms per year, while adding a minimal requirement for diagnostic interpretation, which would optimize sensitivity and false-positive rates."
According to her team's simulations, raising annual requirements for screening volume could lower the number of American women with false-positive workups—by more than 71,000 for annual minimums of 1,000, or by more than 117,000 year for annual minimums of 1,500—without hindering the detection of breast cancer.
On the other hand, raising the volume requirements could cause low-volume radiologists to stop reading mammograms. Concerns have been raised that the cadre of U.S. radiologists who read mammograms is aging and retiring. In this study, for instance, radiologists' median age was 54, and 38 percent of them interpreted fewer than 1,500 mammograms a year.
"The Influence of Annual Interpretive Volume on Screening Mammography Performance in the United States." Collaborating with Dr. Buist were Melissa L. Anderson, M.S., Sebastien J-P.A. Haneuse, Ph.D., Edward A. Sickles, M.D., Robert A. Smith, Ph.D., Patricia A. Carney, Ph.D., Stephen H. Taplin, M.D., M.P.H., Robert D. Rosenberg, M.D., Berta M. Geller, Ed.D., Tracy L. Onega, Ph.D., Barbara S. Monsees, M.D., Lawrence W. Bassett, M.D., Bonnie C. Yankaskas, Ph.D., Joann G. Elmore, M.D., M.P.H., Karla Kerlikowske, M.D., and Diana L. Miglioretti, Ph.D.; Radiology online Feb 22, 2011.