Molina-Hernández Miguel, Gonçalves Patrícia, Chi Yujie, Seco João
German Cancer Research Center, Biomedical Physics in Radiation Oncology, Heidelberg, Germany.
Laboratory of Instrumentation and Experimental Particles Physics, Lisbon, Portugal.
ArXiv. 2025 Sep 3:arXiv:2509.03313v1.
Ultra-high dose rate irradiations to water indicate an enhancement of radical-radical reactions, which could potentially correlate with the Flash effect. The purpose of this work was to extend gMicroMC to support multiple pulse simulations and Flash dose rates, and to investigate, in a pure water model, the mechanisms underlying the enhancement of radical-radical reactions under Flash conditions. gMicroMC, a GPU-based Monte Carlo track-structure algorithm, was extended to simulate multiple pulses. Pure water was exposed to multiple 70 MeV protons pulses delivering up to 20 Gy. The pulse dose rate was set to 2 · 10 and 10 Gy/s, while the average dose rate ranged from 0.01 to 100000 Gy/s. The G-values of HO were used to monitor the influence of dose rate on radical-radical reactions. The multiple pulse extension of gMicroMC was validated against Kinetiscope. Multiple pulse simulations indicated an average dose rate threshold. Below it, complete radical depletion occurred within the pulses, leading to constant G-values. Above it, reactive species accumulated throughout the irradiation, resulting in an increase of radical-radical reactions and thus the G-values of HO. The average dose rate thresholds were in the order of 10 and 100 Gy/s for pulse dose rates of 2 · 10 and 10 Gy/s, respectively. At ultra-high dose rates, the brief intervals between pulses led to a reactive species build-up, which enhanced radical-radical reactions. This build-up is more likely to promote radical-radical reactions than the inter-track mechanism. The advancements in gMicroMC provide a sophisticated tool to study chemical dose rate dependencies.
对水进行的超高剂量率辐照表明自由基-自由基反应增强，这可能与闪光效应相关。本工作的目的是扩展gMicroMC以支持多脉冲模拟和闪光剂量率，并在纯水模型中研究闪光条件下自由基-自由基反应增强的潜在机制。gMicroMC是一种基于GPU的蒙特卡罗径迹结构算法，已被扩展以模拟多脉冲。纯水受到多个70 MeV质子脉冲辐照，剂量高达20 Gy。脉冲剂量率设定为2·10和10 Gy/s，而平均剂量率范围为0.01至100000 Gy/s。使用HO的G值来监测剂量率对自由基-自由基反应的影响。gMicroMC的多脉冲扩展已通过Kinetiscope验证。多脉冲模拟表明存在平均剂量率阈值。低于该阈值时，脉冲内自由基完全耗尽，导致G值恒定。高于该阈值时，反应性物种在整个辐照过程中积累，导致自由基-自由基反应增加，从而使HO的G值增加。对于2·10和10 Gy/s的脉冲剂量率，平均剂量率阈值分别约为10和100 Gy/s。在超高剂量率下，脉冲之间的短暂间隔导致反应性物种积累，增强了自由基-自由基反应。这种积累比径迹间机制更有可能促进自由基-自由基反应。gMicroMC的进展为研究化学剂量率依赖性提供了一个精密工具。
