Effects of nuclear interaction corrections and trichrome fragment spectra modelling on dose and linear energy transfer distributions in carbon ion radiotherapy.

Background And Purpose: Nuclear interaction correction (NIC) and trichrome fragment spectra modelling improve relative biological effectiveness-weighted dose (D) and dose-averaged linear energy transfer (LET) calculation for carbon ions. The effect of those novel approaches on the clinical dose and LET distributions was investigated.

Materials And Methods: The effect of the NIC and trichrome algorithm was assessed, creating single beam plans for a virtual water phantom with standard settings and NIC + trichrome corrections. Reference D and LET distributions were simulated using FLUKA version 2021.2.9. Thirty clinically applied scanned carbon ion treatment plans were recalculated applying NIC, trichrome and NIC + trichrome corrections, using the LEM low dose approximation and compared to clinical plans (). Four treatment sites were analysed: six prostate adenocarcinoma, ten head and neck, nine locally advanced pancreatic adenocarcinoma and five sacral chordoma. The FLUKA and clinical plans were compared in terms of D deviations for D, D, D for the clinical target volume (CTV) and D in ring-like dose regions retrieved from isodose curves in plans. Additionally, region-based median LET deviations and global gamma parameters were evaluated.

Results: Dose deviations comparing and evaluation plans were within ± 1% supported by γ-pass rates over 97% for all cases. No significant LET deviations were reported in the CTV, but significant median LET deviations were up to 80% for very low dose regions.

Conclusion: Our results showed improved accuracy of the predicted D and LET. Considering clinically relevant constraints, no significant modifications of clinical protocols are expected with the introduction of NIC + trichrome.