Breast cancer screening with x-ray mammography, using one or two projection images of the breast, is an indispensible tool in the early detection of breast cancer in women. Digital breast tomosynthesis (DBT) is a 3D imaging technique that promises higher sensitivity and specificity in breast cancer screening at a similar radiation dose to conventional two-view screening mammography. In DBT a 3D volume is reconstructed with anisotropic voxels from a limited number of x-ray projection images acquired over a limited angle. Although the benefit of early cancer detection through screening mammography outweighs the potential risks associated with radiation, the radiation dosage to women in terms of mean glandular dose (MGD) is carefully monitored. This work studies the MGD arising from a prototype DBT system under various parameters. Two anode/filter combinations (W/Al and W/Al+Ag) were investigated; the tube potential ranges from 20 to 50 kVp; and the breast size varied between 4 and 10 cm chest wall-to-nipple distance and between 3 and 7 cm compressed breast thickness. The dosimetric effect of breast positioning with respect to the imaging detector was also reviewed. It was found that the position of the breast can affect the MGD by as much as 5% to 13% depending on the breast size.

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Digital breast tomosynthesis (DBT) is a 3D breast imaging technique that has the potential of replacing the existing 2D techniques. DBT reconstructs the 3D images from limited number of projection angles and each image slice removes the overlying tissues that obstruct the detection of small tumours and microcalcifications. In this study, we compared DBT and its 2D counterpart using the Monte Carlo method with DeBRa, an advanced computational breast model. DeBRa was modeled in MCNPX together with a hypothetical DBT system ofW/AI+Ag xray source/filter combination and a-Se detector. Simulation results show consistently that DBT allows detection of smaller tumours and smaller microcalcifications than the 2D images. This lays the basis for further large scale simulation studies with more variability in the breast model and in the system configurations.

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