A Monte Carlo model for mean glandular dose evaluation in spot compression mammography

Abstract

Purpose To characterize the dependence of normalized glandular dose (DgN) on various breast model and image acquisition parameters during spot compression mammography and other partial breast irradiation conditions, and evaluate alternative previously-proposed dose-related metrics for this breast imaging modality. Methods Using Monte Carlo simulations with both simple homogeneous breast models and patient-specific breasts, three different dose related metrics for spot compression mammography were compared: the standard DgN, the normalized glandular dose to only the directly irradiated portion of the breast (DgNv), and the DgN obtained by the product of the DgN for full field irradiation and the ratio of the mid-height area of the irradiated breast to the entire breast area (DgNM). How these metrics vary with field-of-view size, spot area thickness, x-ray energy, spot area and position, breast shape and size, and system geometry was characterized for the simple breast model and a comparison of the simple model results to those with patient-specific breasts was also performed. Results DgN in spot compression mammography can vary considerably with breast area. However, the difference in breast thickness between the spot compressed area and the uncompressed area does not introduce a variation in DgN. As long as the spot compressed area is completely within the breast area and only the compressed breast portion is directly irradiated, its position and size does not introduce a variation in DgN for the homogeneous breast model. As expected, DgN is lower than DgNv for all partial breast irradiation areas, especially when considering spot compression areas within the clinically used range. DgNM underestimates DgN by 6.7% for a W/Rh spectrum at 28 kVp and for a 9×9 cm2 compression paddle. Conclusion As part of the development of a new breast dosimetry model, a task undertaken by the American Association of Physicists in Medicine and the European Federation of Organizations of Medical Physics, these results provide insight on how DgN and two alternative dose metrics behave with various image acquisition and model parameters.

Homogeneous vs. patient specific breast models for Monte Carlo evaluation of mean glandular dose in mammography

“…As shown in previous papers [19,22], adopting heterogeneous breast phantoms with voxels randomly placed within the breasts and filled with either glandular tissue or adipose tissue, leads to different results, with respect to homogeneous phantoms composed of a homogeneous mixture of adipose and glandular tissue. In this paper, we compare MGD and glandular dose calculated by adopting standard homogeneous breast models to that evaluated with patient specific breast phantoms.…”

“…A MC code for MGD calculation in X-ray breast imaging was developed and presented in previous papers [19,[21][22][23][24]. It is based on GEANT4 ver.…”

“…[16] and adopted in Ref. [22]. They reproduced the anatomy and shape characteristics of the breast undergoing compression during mammographic examinations (Fig.…”

“…In this paper, we compare MGD and glandular dose calculated by adopting standard homogeneous breast models to that evaluated with patient specific breast phantoms. Since the MC code here adopted for the glandular dose computation for heterogeneous breast phantoms is different from those of previous works [19,22], we performed a further validation test. We produced 9 voxelised breast phantoms with a semi-circular cross section with a radius of 10 cm and with a skin layer of 0.2 cm.…”

Internal breast dosimetry in mammography: Experimental methods and Monte Carlo validation with a monoenergetic x‐ray beam

“…Although in this way a different material can be assigned to each voxel, in this work, all voxels are defined as representing the 50% glandular composition of the CIRS phantom, as specified by Byng et al It should be noted that the chemical composition and density described by Byng et al is slightly different from the one commonly used for breast applications but it replicates, to the best of our knowledge, the phantom employed in this study. No difference was found if the phantom is modeled as a simple solid or as a voxel‐based solid …”