Objective: To assess the accuracy and computational performance of a stochastic differential equation (SDE)--based model for proton beam dose calculation by benchmarking against Geant4 in simplified phantom geometries. Approach: Building on Crossley et al. (2025), we implemented the SDE model using standard approximations to interaction cross sections and mean excitation energies, enabling straightforward adaptation to new materials and configurations. The model was benchmarked against Geant4 in homogeneous, longitudinally heterogeneous and laterally heterogeneous phantoms to assess depth--dose behaviour, lateral transport and material heterogeneities. Main results: Across all phantoms and beam energies, the SDE model reproduced the main depth--dose characteristics predicted by Geant4, with proton range agreement within 0.2 mm for 100 MeV beams and 0.6 mm for 150 MeV beams. Voxel--wise comparisons yielded gamma pass rates exceeding 95% under 2%/0.5 mm criteria with a 1% dose threshold. Differences were localised to steep dose gradients or material interfaces, while overall lateral beam dispersion was well reproduced. The SDE model achieved speed-up factors of about 2.5--3 relative to single-threaded Geant4. Significance: The SDE approach reproduces key dosimetric features with good accuracy at lower computational cost and is amenable to parallel and GPU implementations, supporting fast proton therapy dose calculations.

翻译：目的：通过对比简化体模几何结构下的 Geant4 模拟，评估基于随机微分方程（SDE）的质子束剂量计算模型的准确性和计算性能。方法：在 Crossley 等人（2025）的研究基础上，我们采用标准近似方法处理相互作用截面和平均激发能，实现了 SDE 模型，使其能够便捷地适应新材料和新配置。该模型与 Geant4 在均匀、纵向非均匀和横向非均匀体模中进行了基准测试，以评估深度剂量行为、横向输运和材料非均匀性。主要结果：在所有体模和束流能量下，SDE 模型再现了 Geant4 预测的主要深度剂量特征，100 MeV 束流质子射程一致性在 0.2 mm 以内，150 MeV 束流在 0.6 mm 以内。基于体素的比较在2%/0.5 mm判据和1%剂量阈值下，伽马通过率超过95%。差异主要集中在陡峭剂量梯度或材料界面区域，而整体横向束流弥散得到良好再现。SDE 模型相对于单线程 Geant4 实现了约2.5-3倍的加速比。意义：SDE 方法以较低计算成本准确重现了关键剂量学特征，且兼容并行计算和GPU实现，支持快速质子治疗剂量计算。