Department of Radiation Oncology, University of California San Francisco, San Francisco, CA, United States of America. Author to whom any correspondence should be addressed.
Phys Med Biol. 2018 May 17;63(10):105014. doi: 10.1088/1361-6560/aac04c.
Simulation of water radiolysis and the subsequent chemistry provides important information on the effect of ionizing radiation on biological material. The Geant4 Monte Carlo toolkit has added chemical processes via the Geant4-DNA project. The TOPAS tool simplifies the modeling of complex radiotherapy applications with Geant4 without requiring advanced computational skills, extending the pool of users. Thus, a new extension to TOPAS, TOPAS-nBio, is under development to facilitate the configuration of track-structure simulations as well as water radiolysis simulations with Geant4-DNA for radiobiological studies. In this work, radiolysis simulations were implemented in TOPAS-nBio. Users may now easily add chemical species and their reactions, and set parameters including branching ratios, dissociation schemes, diffusion coefficients, and reaction rates. In addition, parameters for the chemical stage were re-evaluated and updated from those used by default in Geant4-DNA to improve the accuracy of chemical yields. Simulation results of time-dependent and LET-dependent primary yields G (chemical species per 100 eV deposited) produced at neutral pH and 25 °C by short track-segments of charged particles were compared to published measurements. The LET range was 0.05-230 keV µm. The calculated G values for electrons satisfied the material balance equation within 0.3%, similar for protons albeit with long calculation time. A smaller geometry was used to speed up proton and alpha simulations, with an acceptable difference in the balance equation of 1.3%. Available experimental data of time-dependent G-values for [Formula: see text] agreed with simulated results within 7% ± 8% over the entire time range; for [Formula: see text] over the full time range within 3% ± 4%; for HO from 49% ± 7% at earliest stages and 3% ± 12% at saturation. For the LET-dependent G, the mean ratios to the experimental data were 1.11 ± 0.98, 1.21 ± 1.11, 1.05 ± 0.52, 1.23 ± 0.59 and 1.49 ± 0.63 (1 standard deviation) for [Formula: see text], [Formula: see text], H, HO and [Formula: see text], respectively. In conclusion, radiolysis and subsequent chemistry with Geant4-DNA has been successfully incorporated in TOPAS-nBio. Results are in reasonable agreement with published measured and simulated data.
水辐射分解及其后续化学过程的模拟为研究电离辐射对生物物质的影响提供了重要信息。Geant4 蒙特卡罗工具包通过 Geant4-DNA 项目添加了化学过程。TOPAS 工具简化了使用 Geant4 进行复杂放射治疗应用的建模，而无需高级计算技能，从而扩大了用户群体。因此，正在开发 TOPAS 的新扩展 TOPAS-nBio，以方便配置基于 Geant4-DNA 的轨迹结构模拟以及用于放射生物学研究的水辐射分解模拟。在这项工作中，在 TOPAS-nBio 中实现了辐射分解模拟。用户现在可以轻松地添加化学物质及其反应，并设置参数，包括分支比、离解方案、扩散系数和反应速率。此外，还重新评估和更新了化学阶段的参数，以提高化学产率的准确性。比较了在中性 pH 和 25°C 下由短带电粒子轨迹段产生的时间依赖性和 LET 依赖性初级产率 G（每 100eV 沉积的化学物质种类）的模拟结果与已发表的测量结果。LET 范围为 0.05-230keV µm。电子的计算 G 值在 0.3%以内满足物质平衡方程，与质子相似，尽管计算时间较长。较小的几何形状用于加速质子和 alpha 模拟，在平衡方程中存在 1.3%的可接受差异。[Formula: see text]的时间依赖性 G 值的可用实验数据在整个时间范围内与模拟结果相差在 7% ± 8%以内；对于[Formula: see text]，在整个时间范围内相差在 3% ± 4%以内；对于 HO，在最早的阶段相差 49% ± 7%，在饱和阶段相差 3% ± 12%。对于 LET 依赖性 G，与实验数据的平均比值分别为 1.11 ± 0.98、1.21 ± 1.11、1.05 ± 0.52、1.23 ± 0.59 和 1.49 ± 0.63（1 个标准差），分别用于[Formula: see text]、[Formula: see text]、H、HO 和[Formula: see text]。总之，成功地将 Geant4-DNA 的辐射分解及其后续化学过程整合到 TOPAS-nBio 中。结果与已发表的测量和模拟数据基本一致。
