Digital mammography screening: Average glandular dose and first performance parameters

Purpose: The Radiation Protection Commission demanded structured implementation of digital mammography screening in Germany. The main requirements were the installation of digital reference centers and separate evaluation of the fully digitized screening units. Digital mammography screening must meet the quality standards of the European guidelines and must be compared to analog screening results. We analyzed early surrogate indicators of effective screening and dosage levels for the first German digital screening unit in a routine setting after the first half of the initial screening round. Materials and Methods: We used three digital mammography screening units (one full-field digital scanner [DR] and two computed radiography systems 1CRI). Each system has been proven to fulfill the requirements of the National and European guidelines. The radiation exposure levels, the medical workflow and the histological results were documented in a central electronic screening record. Results: In the first year 11,413 women were screened (participation rate 57.5%). The parenchymal dosages for the three marnmographic X-ray systems, averaged for the different breast sizes, were 0.7 (DR), 1.3 (CR), 1.5 (CR) mGy. 7% of the screened women needed to undergo further examinations. The total number of screen-detected cancers was 129 (detection rate 1.1 %). 21 % of the carcinomas were classified as ductal carcinomas in situ, 40% of the invasive carcinomas had a histological size <= 10mm and 61 % < 15 mm. The frequency distribution of pTcategories of screen-detected cancer was as follows: pTis 20.9%, pTl 61.2%, pT2 14.7%, pT3 2.3%, pT4 0.8%. 73% of the invasive carcinomas were node-negative. Conclusion: The average glandular dose for all three digital screening units was below the AGD of the analog mammography screening units (1.7 m ' Gy) used in the German trial projects. Nevertheless, the performance indicators of the European guidelines were fulfilled with respect to the prevalent tumor detection rate and tumor size distribution while meeting an acceptable recall rate. This first evaluation of a digital screening unit in Germany demonstrates that the quality standards are met at lower radiation dosage levels than in screen-film mammography.