Absorbed dose in PMMA and equivalent breast phantom in a digital breast tomosynthesis system: Monte Carlo assessment

Abstract

Digital breast tomosynthesis (DBT) is a screening and diagnostic modality that acquires images of the breast at multiple angles during a short scan. The Selenia Dimensions (Hologic, Bedford, Mass) DBT system can perform both fullfield digital mammography and DBT. The system acquires 15 projections over a 15° angular range (from -7.5° to +7.5°). The estimation of breast dose is an important part of mammographic quality control for x-ray mammography. Nevertheless, there are presently no standard protocols for dosimetry of breast imaging in 3D. The purpose of this work was to assess the absorbed dose by projection angle in slabs of polymethyl methacrylate (PMMA) and breast equivalent thickness using the Monte Carlo code MCNPX and typical x-ray energy range (25, 28, 31, 34, 37 and 40 kVp) recommended for breast tomosynthesis. Absorbed dose is a nearly linear function of glandularity, independently of x-ray spectra and decrease with increased PMMA thickness. Taking into account 45 mm thick PMMA and 53 mm thick equivalent breast, the difference in absorbed dose by projection angle has been up to 1.33%, 3.83% e 10.98% for x-ray energies of 25, 28 and 40 kVp, respectively. Normalized glandular dose (DgN) values may be used directly to measure the glandular dose in DBT quality control procedures.