Validation of Light–Ion Quantum Molecular Dynamics (LIQMD) model for hadron therapy

Purpose: This study aims to validate the Light-Ion Quantum Molecular Dynamics (LIQMD) model, an advanced version of the QMD model for more accurate simulations in hadron therapy, incorporated into Geant4 (release 11.2). Methods: Two sets of experiments are employed. The first includes positron-emitter distributions along the beam path for 350 MeV/u ¹²C ions incident on a PMMA target, obtained from in–vivo Positron Emission Tomography (PET) experiments at QST (Chiba, Japan). The second comprises cross-sections for 95 MeV/u ¹²C ions incident on thin targets (H, C, O, Al, and Ti), obtained from experiments at GANIL (Caen, France). The LIQMD model's performance is compared with the experimental data and the default QMD model results. Results: The LIQMD model can predict the profile shape of positron-emitting radionuclide yields with better accuracy than the default QMD model, although some discrepancies remains. The consistency observed in the production of positron-emitting radionuclides aligns with the thin target cross-section analysis. The LIQMD model significantly improves the differential and double-differential cross-sections of fragments produced in thin targets, especially in the forward direction. The overestimation of ¹⁰C production in the in–vivo PET benchmark is consistent with the 95 MeV/u ¹²C cross-section test. Overall, the LIQMD model demonstrates better agreement with experimental measurements for nearly all fragment species compared to the QMD model. Conclusions: The LIQMD model offers an improved description of the fragmentation process in hadron therapy. Future work should involve further validation against additional experimental measurements to confirm these findings.