Machine Description File-based Monte Carlo Simulation Modeling and its Validation Using Pencil Beam Scanning Proton Therapy Commissioning Data

Purpose: This study aims to detail the machine description file (MDF)-based modeling and validation of the independent Monte Carlo (MC) dose engine using commissioning beam data of a multi-gantry Proteus Plus proton pencil beam scanning (PBS) machine, also, enhancing the understanding of its operational parameters and clinical applications. Materials and Methods: The commissioning of the PBS machine involved measuring key parameters such as integrated depth dose, spot size, and absolute dose using calibrated detectors and ionization chambers. These measurements facilitated the modeling of parameters like energy spread and spot tuning within the RayStation treatment planning system and the tool for particle simulation (TOPAS) Geant4-based MC framework. The validation process employed a MDF containing commissioning beam data, assessing 36 spread-out Bragg peak plans by evaluating range, modulation, distal dose fall-off, and lateral profile characteristics at varying depths. In addition, five patient-specific quality assurance (PSQA) plans were created to evaluate nonhomogeneous fields, following American Association of Physicists in Medicine TG report 185 guidelines. Results: The validation results indicated strong agreement between modeled and measured data, with acceptable comparisons observed between RayStation and TOPAS outputs for homogeneous fields. Nonhomogeneous PSQA results demonstrated that over 95% of cases met the gamma passing criteria of 3%/3 mm. Furthermore, assessments of water equivalent thickness in heterogeneous tissues – such as muscle, fat, bone, and liver – showed discrepancies within 0.5% of the range uncertainty, confirming the accuracy of the modeling approach. Conclusion: The MDF-based modeling and validation process is a robust and practical approach for clinical environments, effectively supporting proton therapy research and ensuring quality assurance in treatment planning. The methodologies developed in this study provide valuable insights and tools for researchers utilizing TOPAS MC as a clinical research instrument, paving the way for advancements in proton therapy techniques and patient-specific treatment plans.