Author: Rodrigo T Massera, Sofia Giaccone Thomaz, Alessandra Tomal, Giovanna Tramontin 👨🔬
Affiliation: Universidade Estadual de Campinas. Instituto de Física Gleb Wataghin, Department of Imaging & Pathology, unit of Medical Physics & Quality Assessment, KU Leuven 🌍
Purpose: Monte Carlo simulations are increasingly used in breast dosimetry for their precision in estimating difficult-to-measure quantities, such as glandular dose. With ionizing radiation in breast imaging, dosimetry studies are crucial for analyzing risks, but they usually provide insights about the average glandular dose (Dg) without accounting for hot spots. Therefore, this work explores dose mapping in breasts, which is a growing field aimed at improving the understanding of dose distribution.
Methods: Four breast imaging modalities, Digital Mammography (DM), Contrast-Enhanced Mammography (CEDM), Digital Breast Tomosynthesis (DBT), and Breast Computed Tomography (bCT), were simulated using MCGPU-PSF (VICTRE-1.5). The anthropomorphic voxelized breast phantoms were generated with BreastPhantom software. In addition, voxelized phantoms were assigned based on different glandular tissue samplings: gaussian (centered and lower), and homogeneous, considering both uncompressed and compressed geometry. Nine phantoms were selected and categorised into three groups based on breast thickness, with each group having three different glandularities. For each phantom, the glandular dose distributions (GDDs) were analysed using histograms of glandular voxel dose (GVD) and glandular dose along each axis.
Results: For the thinnest breast phantom, with 14% glandularity, the percentage of voxels where GVD exceeds the average glandular (Dg) dose is highest for bCT (50%) and lowest in DM (41%), while maximum GVD/Dg ratio is higher in DM (5.84) and lower in bCT (1.75). In addition, as the beam effective energy decreases, the maximum ratio increases. For the glandular sampling methods in general, homogeneous has the lowest percentage of voxels exceeding Dg, and gaussian the highest. When breast thickness increases at constant beam energy, the percentage of voxels exceeding Dg decreases.
Conclusion: Dose mapping provides complementary information in breast dosimetry, especially about hot spots. Therefore, it could be an important tool when analyzing the risk of ionizing radiation.