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Standardizing Monte Carlo simulation parameters for a reproducible dose-averaged linear energy transfer.
Wei Yang Calvin Koh1, Hong Qi Tan2, Khong Wei Ang2
1Division of Physics and Applied Physics, Nanyang Technological University, Singapore, Singapore.
The British Journal of Radiology
|July 16, 2020
Summary
We recommend specific GEANT4 simulation parameters (0.05 mm step length, 0.01 mm range cut) for accurate dose-averaged linear energy transfer (LET_D) calculations in proton therapy. Standardizing these parameters improves RBE calculations and cross-institutional data comparison.
Area of Science:
- Medical Physics
- Radiation Oncology
- Computational Science
Background:
- Dose-averaged linear energy transfer (LET_D) is crucial for proton therapy treatment planning and determining relative biological effectiveness (RBE).
- Monte Carlo (MC) simulations are typically used to determine LET_D, but a lack of standardized protocols affects accuracy.
- Simulation parameters, such as maximum step length and range cut, influence secondary electron production and thus dose distribution and LET_D accuracy.
Purpose of the Study:
- To investigate the impact of varying step length and range cut parameters in GEANT4 simulations on LET_D sampling.
- To compare different MC scoring methods for LET_D and identify optimal parameter settings.
- To provide recommendations for standardized simulation protocols for LET_D in proton therapy.
Main Methods:
- Utilized a clinically relevant voxel geometry for MC simulations with varying step length and range cut values.
- Implemented and compared different LET_D scoring methods.
- Applied the concept of covariance between energy deposition per step and step length to explain observed differences.
Main Results:
- Recommended a maximum step length of 0.05 mm and a range cut of 0.01 mm for consistent LET_D values across scoring methods.
- Observed variations up to 200% in LET_D at the plateau of an 80 MeV proton beam due to different scoring methods.
- Identified 'Method one' as yielding one of the lowest percentage differences across simulation parameters.
Conclusions:
- Established optimal GEANT4 parameters (0.05 mm step length, 0.01 mm range cut) for LET_D scoring in a 1 mm voxelized geometry.
- Emphasized the need for clearly defined and standardized LET_D scoring methods to facilitate cross-institutional studies.
- Highlighted that standardized simulation protocols for LET_D will reduce discrepancies and improve RBE calculations in proton therapy.
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