Quality control of the physical and technical aspects of mammography in the Norwegian breast-screening programme

The aim of this study was to establish a system for quality control of technical and physical aspects of mammography in the national Norwegian breast-screening programme, and to evaluate test results obtained during the 4-year pilot project period. Quality control (QC) procedures for the X-ray unit, film and processing, cassettes and screens, view boxes, and image quality were described in two QC manuals. Frequent and relatively simple tests were performed by radiographers on-site and results reported semi-annually to an inspection group established at the Norwegian Radiation Protection Authority (NRPA). Tests requiring special equipment were performed prior to start of screening (first status controls), then annually by the NRPA group, which also assembled and analysed the data from the first 4 years. The analyses were done mainly with reference to stated standard or guidance levels and the degree of deviation from such values. Results for tests of i.a. focal spot size, exposure time, radiation output, mean absorbed glandular dose, reference optical density, sensitometry, and AEC performance are presented. The standard of the equipment tested was in general high. Although some deviations from optimal performance were seen throughout the project, the equipment mostly performed well within the stated limiting values.