Monte Carlo simulation of average glandular dose and an investigation of influencing factors.

This study aims to determine the average absorbed dose of radiation in glandular tissue during mammography and to investigate factors that influence the average glandular dose, particularly the local distribution of glandular tissue within the breast and breast skin thickness. An EGSnrc Monte Carlo code and associated codes were employed in the simulation. The breast voxel models used consist of a homogeneous and heterogeneous mixture of adipose and glandular tissues embedded in a skin layer. The percent depth dose and normalized average glandular dose coefficients for spectra of Mo-Mo target-filter combination were calculated. The results showed good agreement with the experimental results (percent depth dose) and literature values (normalized average glandular dose coefficients) when the breast model is homogeneous. Additional investigation of a heterogeneous breast phantom indicates that the local distribution of glandular tissue within the breast, as well as breast skin thickness, could affect the average glandular dose considerably more than that of a typical homogeneous breast model. This problem may be a concern in most practical situations of breast dosimetry when assessing the radiation risk to patients.