Monte Carlo multiscale modelling of photon and proton distribution in heterogenous tissue

Abstract

Enhancements in radiotherapy treatment outcomes can be realised by minimising uncertainties in dose distribution. Current treatment planning struggles to accurately calculate dose distribution in complex heterogeneous areas, thereby increasing the uncertainty associated with dose distribution. This research focuses on studying microscopic dose distribution in the temporal bone and cochlea. This study utilised an open-access DICOM format dataset for resected temporal bone and cochlea tissue, employing the FLUKA MC code to simulate potential high-dose scenarios in volume-modulated arc therapy using the FLOOD option. Simulations were conducted at 23 photon and proton energy levels, ranging from 0.055 to 5.5 MeV for photons and 37.59–124.83 MeV for protons, to calculate dose distributions. The largest proportion of the dose (48.8%) was deposited in high-density bone at photon energies between 0.055 and 0.09 MeV. Above 0.125 MeV, a notable shift in dose distribution to low-density tissues occurred, reaching a deposition of 53%. In intermediate-density soft bone, dose distribution was 26.4% at 0.07 MeV and decreased to 19.7% at 2.5 MeV, reflecting a 29% difference in dose distribution across the energy spectrum. In proton simulations, dose distribution at low energy (37.59 MeV) revealed no significant changes across low (54.86%), intermediate (19.75%), and high-density (25.39%) areas. Similar patterns were observed at high energy (124.83 MeV), with dose distributions of 54.21% in low-, 19.79% in intermediate-, and 26% in high-density areas. The simulations demonstrated that proton dose distribution was not significantly influenced by tissue heterogeneity in micro-CT data. The photoelectric effect at low energy levels contributed minimally to the dose in soft bone, favouring higher deposition in high-density bone, despite a lower weighting factor at low energies compared with high energies.