Purpose: To retrospectively compare screen-film and full-field digital mammography with soft-copy interpretation for reader performance in detection and classification of breast lesions in women in a screening program.
Materials and methods: Regional ethics committee approved the study; signed patient consents were obtained. Two-view mammograms were obtained with digital and screen-film systems at previous screening studies. Six readers interpreted images. Interpretation included Breast Imaging Reporting and Data System (BI-RADS) and five-level probability-of-malignancy scores. A case was one breast, with two standard views acquired with both screen-film mammography and digital mammography. The standard for an examination with normal findings was classification of normal (category 1) assigned by two independent readers; for cases with benign findings, the standard was benign results at diagnostic work-up in patients who were recalled. Cases with normal or benign findings that manifested as neither interval cancer nor as cancer at subsequent screening were considered the standard. All cancers were confirmed histologically. Images were interpreted by readers in two sessions 5 weeks apart; the same case was not seen twice in any session. Receiver operating characteristic (ROC) analysis and, for a given true-positive fraction, 2 x 2 table analysis and the McNemar test were used. For binary outcome, classification of BI-RADS category 3 or higher was defined as positive for cancer.
Results: Cases with proved findings (n = 232) were displayed: 46 with cancers, 88 with benign findings, and 98 with normal findings. ROC analysis for all readers and all cases revealed a higher area under ROC curve (A(z)) for digital mammography (0.916) than for screen-film mammography (0.887) (P = .22). Five of six readers had a higher performance rating with digital mammography; one of five demonstrated a significant difference in favor of digital mammography with A(z) values; two showed a significant difference in favor of digital mammography with ROC analysis for a given false-positive fraction (P = .01 and .03, respectively). For cases with cancer, digital mammography resulted in correct classification of an average of three additional cancers per reader. For digital versus screen-film mammography, 2 x 2 table analysis for cancers revealed a higher true-positive rate; for benign masses, a higher true-negative rate. Neither of these differences nor any others from analysis of subgroups between the modalities were significant.
Conclusion: Digital mammography allowed correct classification of more breast cancers than did screen-film mammography. A(z) value was higher for digital mammography; this difference was not significant.
RSNA, 2005