MAMMOGRAPHIC FILM DENSITY AND DETECTION OF SMALL BREAST CANCERS

From its inception, the UK National Breast Screening Programme (NHSBSP ) has recognized that optimum image quality of the mammographic screen ing test is a key objective. The overall optical density of the mammog raphy film is one of the factors expected to have a significant effect on the image quality of the mammogram with the potential to influence cancer detection. In a previous review of the performance of mammogra phy equipment in the NHSBSP, it was observed that there was a very wid e range in the mammographic film densities used at different breast sc reening centres. In this study a mammography test object was used to s how experimentally that, for a typical mammography system, image quali ty increased substantially with increased film density. Summary data w as therefore requested from radiologists in the NHSBSP on the rate of detection of small invasive cancers (diam. less than or equal to 10mm) and the typical film density used during that year. Proforma were com pleted for 61 annual sets of results from 31 screening centres involvi ng over 500 000 women. Where centres reported using film densities of less than 1.2D the average small cancer detection rate was 0.12%+/-0.0 1%, as compared to an average of 0.17%+/-0.01% for centres using highe r film densities. The results indicate that there is a need for nation al guidelines in the setting of film densities, and a range for target film densities of 1.4D to 1.8D has been suggested. Attention to optim izing image quality by increasing film density is of particular import ance to any screening centre where film densities of less than 1.2D ar e used, as there may be the potential to increase the detection of sma ll breast cancers by as much as 50%.