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：通过在简化模体几何中与Geant4进行基准测试，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与计算性能。方法：基于Crossley等人（2025）的研究，我们采用相互作用截面和平均激发能的标准近似实现了SDE模型，使其能够直接适配新材料和配置。该模型在均匀、纵向非均匀及横向非均匀模体中与Geant4进行基准比较，以评估其深度-剂量特性、横向输运及材料非均匀性表现。主要结果：在所有模体及束流能量条件下，SDE模型均能复现Geant4预测的主要深度-剂量特征，其中100 MeV质子束的射程吻合度在0.2 mm以内，150 MeV质子束在0.6 mm以内。基于体素的比较显示，在2%/0.5 mm标准（1%剂量阈值）下，伽马通过率超过95%。差异主要集中于陡峭剂量梯度或材料界面区域，而整体横向束流展宽得到良好再现。相较于单线程Geant4，SDE模型实现了约2.5-3倍的加速比。意义：SDE方法能以较低计算成本较精确地复现关键剂量学特征，且适用于并行及GPU实现，为质子治疗剂量快速计算提供了技术支持。