Accuracy of mammography dosimetry in the era of the European Directive 2013/59/Euratom transposition

Purpose: To evaluate the impact of increasing levels of accuracy for mean glandular dose (MGD) evaluation in the era of the European Directive 2013/59/Euratom transposition. Method: 4028 women who had a mammography examination by one of five mammography units using different detector technologies were included in this study. 16,006 images were processed by a software algorithm that determines breast glandularity quantitatively and uses this to estimate patient-specific MGD (psMGD). Entrance dose (ED) values and half value layers (HVLs) measured for each mammography system were collected to evaluate the effect of equipment calibration in psMGD calculation. The psMGD values adjusted for system calibration were compared with organ dose (OD) provided by manufacturers as image metadata. Results: Overall median relative difference between calibrated psMGD and organ dose was below 3%, with larger differences for individual systems. The psMGD adjustment for system calibration was particularly useful for one system for which ED had an evident miscalibration issue. The mean difference between psMGD with calibration and organ dose provided by manufacturers was 4.1 %, ranging from −16.3 % to +24.5 %. The proportion of images for which organ dose was more than 10 % ‘inaccurate’ compared to psMGD was between 11 % and 46 %, depending on the mammography system. Conclusion: Patient-specific mean glandular dose, possibly adjusted for system calibration, allows more accurate individual breast dosimetry than what would be performed using organ dose provided by manufacturers. Conversely, definition of diagnostic reference levels could be achieved using either psMGD or organ dose.