A Monte Carlo study of proton LET calculations: Comparison between the codes PENHAN, FLUKA, and TOPAS

Linear energy transfer (LET) is frequently used to characterize radiation quality in proton therapy and is an important quantity for radiobiological modeling. However, LET calculations can, in principle, vary between Monte Carlo (MC) codes, affecting consistency in treatment planning and relative biological effectiveness (RBE) estimation.

This study aims to investigate the variability of LET results when using different MC codes.

An intercomparison of LET results was performed using penhan, topas MC, and CERN fluka, together with recently published experimental data. Track-averaged ( ${\overline{L}}_t$ ) and dose-averaged ( ${\overline{L}}_d$ ) LET were evaluated under different irradiation configurations, including pencil and broad beams, with and without nuclear reactions.

The results obtained indicate that discrepancies in LET calculations are primarily linked to the choice of stopping powers and the handling of nuclear interactions. Calculations considering only primary protons exhibited great agreement with recent experimental LET measurements, validating our simulations.

${\overline{L}}_t$ showed higher robustness and consistency across codes, suggesting it as potentially a more reliable metric for LET-based treatment planning and RBE modeling. Our findings emphasize the importance of consistent LET calculations, result reporting, and code benchmarking in proton therapy calculations.