Microdosimetric spectra evaluation for proton minibeam radiotherapy through Monte Carlo Geant4 simulations

In vivo/vitro experiments carried out using the proton minibeam radiotherapy technique show a potential advantage in sparing healthy tissue over conventional radiotherapy. Within the INFN MIRO (MInibeam RadiOtherapy) project, we investigated the beam-quality variation along the beam pattern to assess correlations between the physical dosimetric parameters characterizing the beam and the radiobiological outcome. The Geant4 advanced example exp microdosimetry was used to run Monte Carlo simulations of dose distributions in a water phantom with various collimator designs. A silicon microdosimeter inside the phantom records energy deposition within the detector’s active layer to study the variation in the peak and valley regions. This first study reveals distinct variations in the frequency-mean lineal energy across different positions within the beam profile, suggesting new radiobiological effects to investigate. The resulting estimates serve as a foundation for calculating the realtive biological effectiveness used in radiobiological models. This work was partially founded by the European Union - Next Generation EU through Projects Mission 4 Component 2 Inv. 1.5 CUP B83C22003930001.