Comparative analysis of eMC algorithm dose calculations using GATE validation: impact of tissue heterogeneity on electron beam dosimetry.

Abstract

Purpose: Electron beam radiotherapy is a crucial modality for treating superficial tumors. Accurate dose calculation is essential for treatment efficacy and minimizing side effects. While Monte Carlo (MC) simulations are considered the gold standard for dose calculation, their computational cost can be prohibitive. The electron Monte Carlo (eMC) algorithm offers a faster alternative, but its accuracy, especially in heterogeneous environments, remains a concern.

Methods and materials: This study compares electron beam dose distributions calculated using the eMC algorithm in a treatment planning system (TPS) with those obtained from full MC simulations using the GATE platform. We evaluated the eMC algorithm's performance across various electron energies (6, 9, and 12 MeV) and field sizes (6 × 6 cm² to 20 × 20 cm²), in both homogeneous water phantoms and heterogeneous phantoms incorporating lung-equivalent and bone-equivalent materials.

Results: Results in homogeneous phantoms demonstrated generally good agreement between eMC and GATE, with some discrepancies observed in penumbra regions and at higher energies, particularly for larger field sizes. In heterogeneous phantoms, significant deviations were observed, particularly in lateral dose profiles near density interfaces and at higher beam energies, with percentage of points with less than 3% difference dropping considerably.

Conclusion: These findings highlight the limitations of the eMC algorithm in accurately modeling complex tissue heterogeneities. While eMC provides acceptable accuracy in relatively simple scenarios, its performance degrades significantly in clinically realistic heterogeneous environments, necessitating caution in treatment planning and highlighting the ongoing need for improved dose calculation algorithms.