Purpose: Microbeam radiation therapy (MRT) is a treatment modality based on high flux, synchrotron generated x-rays. The negligible beam divergence together with the high x-ray source coherence gives the possibility of spatial fractionation of the radiation beam in a micrometric array to push the dose-volume effect towards its theoretical limits. So far, the most advanced MRT treatment planning system (hybrid dose calculation algorithm) is limited to a macroscopic rendering of the dose and do not account for the special features of MRT. For this reason, a pure Monte Carlo dose calculation engine with micrometric resolution is currently been developed for MRT (penMRT).
Methods: PenMRT, is based on the PENELOPE (2018) Monte Carlo code, modified to take into account the voxelised geometry of the patients (CT-scans) and offering an adaptive micrometric dose calculation grid. To further improve the speed, parallelization using MPI was added together with an optional source replication protocol. The performance of penMRT is compared to its original version (penmain) for a 2x2 cm² incident broad beam and for a 50m x 2cm single microbeam, in terms of dose distribution assessment in a water equivalent phantom. The so-called peak to valley dose ratio (PVDR) obtained in a 2x2 cm² MRT field using penMRT were also compared to the literature.
Results: A good agreement was observed between penmain and penMRT with a maximum relative difference of ±0.05% and ±0.2% in the irradiation field and out-off field, respectively. PVDR values obtained using a spectrum with an average energy of 99 keV are in coherence with the ones found in literature.
Conclusion: This study shows the performances and reliability of penMRT to provide micrometric dose maps for MRT treatments using synchrotron generated x-ray microbeams arrays. The code is now in experimental validation phase using Gafchromic films and microdiamonds detectors.