WE-G-103-08: Retrospective Determination of Personalized Mean Glandular Dose Coefficients for Conventional Mammography Using Heterogeneously-Layered Breast Models

Abstract

Purpose: The heterogeneous distribution of the glandular tissue is overlooked in calculations of mean glandular dose (MGD). In this work, we introduce a methodology for the calculation of patient‐oriented dose conversion coefficients. In addition, we provide an empirical relationship to use for the estimation of these coefficients in a clinical setting. Methods: Breast density assessment software was used to obtain the breast density maps from conventional mammography four‐view sets of images in a group of 31 patients. The glandular tissue distribution for each breast was estimated from the breast density maps using the Mammography‐Image Based (MIB) method presented in this work. The corresponding patient‐oriented dose conversion coefficients (DgN‐HLB) were determined using Monte Carlo methods and a Heterogeneously‐Layered Breast (HLB) geometry. This geometry models the breast core as composed of layers with different glandular percentage, as opposed to a homogeneous breast core. The DgN‐HLB were compared to the corresponding dose conversion coefficients based on a homogeneous core breast geometry (DgN). Results: Differences as high as 49% between the DgN‐HLB and their corresponding DgN were found. The difference between DgN and DgN‐HLB was found to have a linear relationship with the glandular distribution index (I_dist) calculated in this work. This relationship was used to make a patient‐specific correction to the DgN (k_dist) that allows for estimations of DgN‐HLB, without the use of patient‐based Monte Carlo simulations. Both HLB‐based approaches agree within 10.5%. Conclusion: We have developed a method to obtain estimations of the glandular tissue distribution from conventional mammography images using their corresponding breast density maps. Our work provides a methodology to incorporate anatomical information in the calculation of patient‐oriented MGD, thereby overcoming one of the known limitations of the currently used mammography dosimetry methods.