Room: Exhibit Hall | Forum 8
Purpose: To evaluate glandular dose (GD) indices from a glandular dose-to-air kerma volume histogram (GD/K-VH) calculated using realistic heterogeneous breast phantoms (heterogeneous phantoms) in mammography.
Methods: The EGSnrc/BEAMnrc Monte Carlo code was used to simulate a mammographic x-ray tube. The target and filter were Mo/Mo and W/Rh. The heterogeneous phantom was simulated according to the breast model of Hernandez et al. The phantom is a half-ellipsoidal form and composed of adipose tissue, glandular tissue, and an outer skin with a thickness of 1.5 mm. The compressed phantom thickness was 2, 4, and 6 cm. The glandularity was set to 15% to 60%. The GD for heterogeneous voxel phantoms was calculated using simulated x-ray spectra. Similarly, the GD for homogeneous voxel phantoms was calculated at the same irradiation conditions as heterogeneous phantoms. The GD was evaluated from GD/K-VHs which are presented by a glandular volume (%) as a function of the ratio of GD and air kerma (K). The air kerma was also calculated by the Monte Carlo method. The GD indices for all breast phantoms was evaluated with V(MGD) and GDâ‚‚/K from GD/K-VHs. The V(MGD) is the relative glandular volume covered by mean GD (MGD). The GDâ‚‚/K is the GD/K value covering a 2% glandular volume. The MGD/K was also calculated.
Results: Values of MGD/K for the heterogeneous phantom with thickness of 4 cm and 35% glandularity were lower by 30% than those for the homogeneous phantom in Mo/Mo. Similarly, V(MGD) and GDâ‚‚/K were lower by 8.2% and 22%, respectively. In the heterogeneous phantom, the GDâ‚‚/K value was 3.8 times as large as that of MGD/K.
Conclusion: It is useful to evaluate not only existing MGD/K but also GD indices of V(MGD) and GDâ‚‚/K from GD/K-VHs using heterogeneous phantoms in mammography.