Monte Carlo calculation of monoenergetic and polyenergetic DgN coefficients for mean glandular dose estimates in mammography using a homogeneous breast model

We computed normalized glandular dose (DgN) coefficients for mean glandular dose estimates in contemporary 2D mammography units, taking into account a realistic homogeneous model for the breast. We developed a Monte Carlo code based on the simulation toolkit GEANT4 ver. 10.00. The breast was modelled as a cylinder with a semi-cylindrical section with a radius of 10 cm, enveloped in a 1.45-mm thick skin layer, as found out in recent reports from the University of California Davis team in the analysis of breast computed tomography clinical scans. The compressed breast thickness was between 3 cm and 8 cm. The DgN coefficients were calculated for monoenergetic X-ray beams between 4.25 keV and 49.25 keV and were fitted with polynomial curves. Polyenergetic DgN coefficients were then computed for spectra obtained for various anode/filter combinations as adopted in routine clinical practice: Mo/Mo 30 μm (2540 kV), Mo/Rh 25 μm (2540 kV), Rh/Rh 25 μm (2540 kV), W/Ag 50 μm (2634 kV), W/Al 500 μm (2638 kV), W/Al 700 μm (2840 kV) and W/Rh 50 μm (2435 kV). Monoenergetic DgN curve fit coefficients and polyenergetic DgNp coefficients were released for research and clinical work. Polyenergetic DgN coefficients were 6% higher than those provided in the reference literature, on average. The differences ranges between -18% and 30%; 50% of the computed coefficients differed by less than 10%. The dataset of DgN coefficients are provided as tables (49 pages) for varying glandular fraction by mass and compressed breast thickness. Moreover, a computer code has been developed for generating user specific coefficients DgNp for user defined X-ray spectra up to 49 kV, calculated by spectral weighting from the dataset of monoenergetic DgN coefficients.