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Validation of Geant4 fragmentation models for broad beam heavy-ion therapy
Kristie Moore1, Susanna Guatelli1, Yoshihide Sato2
1Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia.
Physics in Medicine and Biology
|July 22, 2026
Summary
Monte Carlo simulations of nuclear fragmentation in heavy-ion therapy (HIT) are crucial for risk assessment. The LiQMD model showed the best agreement for broad beams, but model performance varied with geometry, highlighting the need for diverse validation methods.
Area of Science:
- Medical Physics
- Radiation Oncology
- Nuclear Physics
Background:
- Heavy-ion therapy (HIT) offers precise dose delivery but faces challenges from nuclear fragmentation, creating secondary radiation fields.
- Accurate simulation of these fragmentation fields is vital for estimating healthy tissue risks in HIT.
- Existing validation studies often use millimetre-scale pencil beams, which may not represent centimetre-scale clinical fields.
Purpose of the Study:
- To evaluate the accuracy of four Geant4 nuclear fragmentation models (BIC, INCL, QMD, LiQMD) in simulating secondary radiation fields.
- To compare model performance across different beam geometries (passive broad-beam vs. pencil-beam) and ion types (C, Ne, N, O).
- To determine if conclusions from pencil-beam validation studies are applicable to clinical broad-beam scenarios.
Main Methods:
- Four Geant4 models (BIC, INCL, QMD, LiQMD) were tested.
- Passive broad-beam measurements for 290 MeV/u C and 400 MeV/u Ne ions were compared with simulations.
- Pencil-beam measurements for 400 MeV/u C, 670 MeV/u N, and 670 MeV/u O ions were also compared, including angular distributions.
Main Results:
- For carbon (C) broad beams, the LiQMD model demonstrated the best agreement with experimental data.
- LiQMD also performed best in fragment-yield comparisons for carbon (C) ion pencil beams.
- No single model consistently outperformed others for neon (Ne) broad beams, though LiQMD remained highly accurate.
- Pencil-beam comparisons generally showed better agreement than broad-beam comparisons, indicating geometry's influence on model validation.
Conclusions:
- Validation of nuclear fragmentation models using pencil beams may not directly translate to passive broad-beam clinical scenarios.
- Passive broad-beam measurements offer a crucial complementary validation method for Geant4 fragmentation models.
- Broad-beam data provide additional constraints on fragment angular distributions, lateral transport, and detector acceptance, leading to more robust model assessment.
