Comprehensive Open-Field Dosimetric Validation of Commercially Available Monte Carlo-Based Secondary Dose Verification System for Photon Radiotherapy
Abstract
Purpose
To perform comprehensive dosimetric validation of a commercially available independent Monte Carlo (MC)-based secondary dose calculation engine for clinical photon radiotherapy.
Methods
A suite of open-field dosimetry measurements for 6MV and 10MV flattened and flattening filter free (FFF) photon energies were acquired on a C-arm linear accelerator for validation against MC simulations. A 0.07cc scanning ion chamber was used to measure dose profiles in a homogeneous water phantom, including transverse and radial beam profiles at varying depths (dmax to 30 cm) and percent depth doses (PDDs) spanning clinically useful square-field sizes (ranging from 3x3 to 40x40cm). Analogous three-dimensional (3D) MC simulations were performed with a commercially available secondary dose calculation engine (RadMonteCarlo, Radformation, NY). The number of MC histories per measurement condition was field-size dependent and increased such that the mean statistical uncertainty was less than 0.3%. For a given measured profile, associated MC data were extracted from the simulated 3D dose volumes, which were averaged across all histories. This data was convolved with a Gaussian kernel with a 5 mm FWHM to account for detector volume averaging in measured data. MPPG5a dose difference (DD) and distance-to-agreement (DTA) evaluation criteria were employed to compare measured data against MC simulations.
Results
All measured PDD data points (n=12000) agreed with MC simulations across all energies and field sizes at 2% or 2mm DD/DTA criteria. For cross-plane profiles, all measured points (n=27,964) for 6FFF and 10FFF energies agreed with MC simulations evaluated at 2% DD in-field, 3mm DTA in penumbra, and 3% of maximum field dose out-of-field. Minimal disagreement was observed for 6MV (n=40/13976) and 10MV (n=311/13996) profiles, primarily in the out-of-field regions for large field sizes.
Conclusion
This study provides a comprehensive dosimetric validation of a commercial MC-based secondary dose calculation engine and demonstrates its clinical utility for benchmarking measured data.