Novel PENELOPE geometry subroutine for patient-Specific dosimetry in the presence of electromagnetic fields

Abstract

Technological advancements have enabled the integration of magnetic resonanceimaging with linear accelerators, introducing new dosimetry challenges arising fromstrong magnetic fields within the ionizing radiation field. Notwithstanding the traditionalpengeom subroutine, distributed with the PENELOPE package, adequately tracksparticles in the presence of external electromagnetic fields, it is limited to geometriesdefined by quadric surfaces. Conversely, established developments such as PenEasy,which handle voxelized geometries within the PENELOPE main code, are constrainedin performing particle tracking with external electromagnetic fields. In response, the hereintroduced voxgeom emerges as an innovative geometry subroutine tailored to trackparticles within voxelized regions seamlessly integrated with the PENELOPE main code,even when accounting for external electromagnetic fields. Voxgeom considers each voxelof the geometry as a body in a 3D arrangement, whereas interfaces are treated completelyanalogue to the pengeom subroutine. Furthermore, allows the use of patient-specificinformation to establish a univocal relationship between each body and material files,and integrates the models provided by the PENELOPE package for simulatingJournal Pre-proofelectron/positron transport with external EM fields. Successful performance is obtainedcomparing voxgeom with the well-validated pengeom geometry manager both in absenceand in presence of external strong magnetic fields. Differences up to 2% and 1% arereported between both subroutines, for the homogeneous and inhomogeneous phantomwith magnetic field, respectively. Moreover, parameters such as percentage depth doseat depth of maximum dose, 10, and 20 cm are indistinguishable. Finally, promisingdosimetry outputs are obtained using voxgeom to characterize dosimetry effects due tothe presence of magnetic fields as happens in the Elekta Unity MR-LINAC in arepresentative patient-specific clinical case.