Comparing 2 Monte Carlo Systems in Use for Proton Therapy Research

Area of Science:

• Medical Physics
• Computational Science
• Radiation Transport Simulation

Background:

• Monte Carlo (MC) transport codes are essential tools for medical physics applications.
• Ensuring the accuracy of these codes through continuous cross-validation is critical for reliable clinical use.
• MC² (based on MCNPX) and TOPAS (based on Geant4) are widely used MC codes.

Purpose of the Study:

• To compare the simulation accuracy of MC² and TOPAS in medical physics scenarios.
• To validate the performance of MCNPX and Geant4 based codes through direct comparison.
• To assess the clinical relevance of any observed discrepancies between the two simulation platforms.

Main Methods:

• Simulations were performed using TOPAS and MC² with increasing geometrical complexity.
• Scenarios included water phantoms with monoenergetic beams, phantom with tissue/bone slabs, and voxelized CT geometries.
• Comparisons were based on dose/energy profiles, r90 calculations, and gamma analyses.

Main Results:

• Both MC² and TOPAS yielded highly similar results for simple water phantom simulations.
• Minor systematic differences in r90 values (approx. 0.4%) were noted with bone/lung slabs.
• Excellent agreement was observed in complex CT geometries, with >95% pass rate on 3D gamma analysis (2%/2mm criterion).

Conclusions:

• Discrepancies between MC² and TOPAS simulations were found to be minimal.
• The observed differences were not considered clinically significant for medical physics applications.
• Both MCNPX and Geant4 based codes demonstrate reliable performance for radiation transport simulations.