Université Clermont-Auvergne, CNRS, LPCA, Clermont-Ferrand, France.
Université Bordeaux, CNRS, LP2IB, Gradignan, France.
Med Phys. 2024 Oct;51(10):7500-7510. doi: 10.1002/mp.17281. Epub 2024 Jul 8.
Radiobiological effectiveness of radiation in cancer treatment can be studied at different scales (molecular till organ scale) and different time post irradiation. The production of free radicals and reactive oxygen species during water radiolysis is particularly relevant to understand the fundamental mechanisms playing a role in observed biological outcomes. The development and validation of Monte Carlo tools integrating the simulation of physical, physico-chemical and chemical stages after radiation is very important to maintain with experiments.
Therefore, in this study, we propose to validate a new Geant4-DNA chemistry module through the simulation of water radiolysis and Fricke dosimetry experiments on a proton preclinical beam line.
In this study, we used the GATE Monte Carlo simulation platform (version 9.3) to simulate a 67.5 MeV proton beam produced with the ARRONAX isochronous cyclotron (IBA Cyclone 70XP) at conventional dose rate (0.2 Gy/s) to simulate the irradiation of ultra-pure liquid water samples and Fricke dosimeter. We compared the depth dose profile with measurements performed with a plane parallel Advanced PTW 34045 Markus ionization chamber. Then, a new Geant4-DNA chemistry application proposed from Geant4 version 11.2 has been used to assess the evolution of , , , , , , and reactive species along time until 1-h post-irradiation. In particular, the effect of oxygen and pH has been investigated through comparisons with experimental measurements of radiolytic yields for and Fe.
GATE simulations reproduced, within 4%, the depth dose profile in liquid water. With Geant4-DNA, we were able to reproduce experimental radiolytic yields 1-h post-irradiation in aerated and deaerated conditions, showing the impact of small changes in oxygen concentrations on species evolution along time. For the Fricke dosimeter, simulated G(Fe) is 15.97 ± 0.2 molecules/100 eV which is 11% higher than the measured value (14.4 ± 04 molecules/100 eV).
These results aim to be consolidated by new comparisons involving other radiolytic species, such as or to further study the mechanisms underlying the FLASH effect observed at ultra-high dose rates (UHDR).
辐射在癌症治疗中的放射生物学效应可以在不同的尺度（从分子到器官）和不同的辐照后时间进行研究。水辐射分解过程中自由基和活性氧物质的产生对于理解在观察到的生物学结果中起作用的基本机制特别重要。开发和验证整合辐射后物理、物理化学和化学阶段模拟的蒙特卡罗工具对于与实验保持一致非常重要。
因此，在这项研究中，我们通过在质子临床前束线上模拟水辐射分解和 Fricke 剂量测定实验，提出验证一种新的 Geant4-DNA 化学模块。
在这项研究中，我们使用 GATE 蒙特卡罗模拟平台（版本 9.3）模拟由 IBA Cyclone 70XP 等时回旋加速器产生的 67.5 MeV 质子束，在常规剂量率（0.2 Gy/s）下模拟超纯水样品和 Fricke 剂量计的辐照。我们将深度剂量分布与使用平面平行的先进 PTW 34045 Markus 电离室进行的测量进行了比较。然后，使用源自 Geant4 版本 11.2 的新 Geant4-DNA 化学应用程序来评估 、 、 、 、 、 和 等活性物质在辐照后 1 小时内随时间的演化。特别是，通过比较 和 Fe 的辐解产率的实验测量，研究了氧和 pH 的影响。
GATE 模拟在 4%的范围内再现了液体水中的深度剂量分布。使用 Geant4-DNA，我们能够在有氧和无氧条件下再现辐照后 1 小时的实验 辐解产率，表明氧浓度的微小变化对随时间的物种演化的影响。对于 Fricke 剂量计，模拟的 G(Fe)为 15.97±0.2 个分子/100 eV，比测量值（14.4±04 个分子/100 eV）高 11%。
这些结果旨在通过涉及其他辐解产物（如 或 ）的新比较来得到巩固，以进一步研究在超高剂量率（UHDR）下观察到的 FLASH 效应的机制。
