Technical Note: MC-GPU breast dosimetry validations with other Monte Carlo codes and Phase Space File implementation

Purpose: To validate the MC-GPU Monte Carlo code for dosimetric studies in x-ray breast imaging modalities: mammography, digital breast tomosynthesis, contrast enhanced digital mammography and breast-CT. Moreover, to implement and validate a phase space file generation routine. Methods: The MC-GPU code (v. 1.5 DBT) was modified in order to generate phase space files and to be compatible with PENELOPE v. 2018 derived cross section database. Simulations were performed with homogeneous and anthropomorphic breast phantoms for different breast imaging techniques. The glandular dose was computed for each case and compared with results from the PENELOPE (v. 2014) + penEasy (v. 2015) and egs brachy (EGSnrc) Monte Carlo codes. Afterwards, several phase space files were generated with MC-GPU and the scored photon spectra were compared between the codes. Results: MC-GPU showed good agreement with the other codes when calculating the glandular dose distribution for mammography, mean glandular dose for digital breast tomosynthesis, and normalized glandular dose for breast-CT. The latter case showed average/maximum relative differences of 2.3%/27%, respectively, compared to other literature works, with the larger differences observed at low energies (around 10 keV). The recorded photon spectra entering a voxel were similar (within statistical uncertainties) between the three Monte Carlo codes. Conclusions: The results indicate that MC-GPU code is suitable for breast dosimetric studies for different x-ray breast imaging modalities, with the advantage of a high performance. The phase space file implementation was validated and is compatible with the IAEA standard, allowing multiscale Monte Carlo simulations with a combination of CPU and GPU codes.