A Clinical Validation of the Egs_Mird Monte Carlo Code for Patient-Specific Dose Calculations
Abstract
Purpose
To test egs_mird as an independent verification for patient-specific dosimetry calculations in a clinical workflow alongside two commercially available software packages (MIM SurePlanTM MRT and Voximetry TorchMCTM).
Methods
TRT patients were scanned using a Siemens Symbia Intevo Excel approximately 72 hours post-injection. CT and quantitative SPECT image data for seven patients were imported into both TorchMC and MIM SurePlan MRT, which utilize voxel S-value (VSV) and GPU-based Monte Carlo methods, respectively, to calculate the absorbed dose. All software solutions employed the Hänscheid method to approximate cumulative biological decay. The SPECT/CT images were converted into an EGSnrc-compatible format using a combination of tools available online and in-house MATLAB code. Gamma index analysis compared doses where egs_mird results were > 2.5Gy with 1%/3mm agreement criteria and organ-average doses were compared for the kidneys and the parotids.
Results
The average 1%/3mm local gamma agreement between egs_mird and MIM was 97.7% ± 1.61% and 63.3% ± 5.61% between egs_mird and Torch. The average percent difference between patient-specific organ average doses calculated by MIM and egs_mird with all voxels assigned water was 2.05% ± 6.22% (0.11 Gy ± 0.05 Gy) for the kidneys and 2.12% ± 6.33% (0.07 Gy ± 0.07 Gy) for the parotids. The corresponding results between Torch and egs_mird using heterogeneous material assignments were 7.25% ± 1.06% (0.15 Gy ± 0.06 Gy) for the kidneys and 7.82% ± 2.12% (0.10 Gy ± 0.10 Gy) for the parotids.
Conclusion
Doses calculated using egs_mird can be used as part of a clinical workflow to independently verify doses calculated using commercial software. Underlying differences in heterogeneity modeling, radiation transport, variance reduction, and other simplifications to increase efficiency likely led to differences in calculated doses between the software. Patient-specific organ doses varied despite each being given the same injected activity.