摘 要：为探究γ射线诱发 DNA 单链断裂（SSB）的早期辐射化学过程，本研究利用蒙特卡罗模拟工具TOPAS及其拓展模块TOPAS-nBio，构建水球-质粒微观模拟模型，模拟60Coγ射线在水性环境下辐照超螺旋质粒pUC19，并诱发质粒 DNA SSB的过程。本研究在系统改变辐射剂量、DNA质量浓度以及羟基自由基（·OH）清除剂浓度的条件下，对 SSB 产额进行量化比较。模拟结果显示：SSB产额随辐射剂量增加呈现上升趋势；环境中DNA质量浓度越高，SSB绝对产额呈近似线性增加，但单位质量DNA的损伤效率随浓度升高而降低；·OH清除剂浓度增加可大幅降低SSB产额，·OH清除能力对SSB形成有显著抑制作用。本研究结果为放射治疗优化、辐射防护策略制定以及核环境健康风险评估提供了一定的理论支持。
关键词：伽马射线；质粒DNA；自由基；蒙特卡罗模拟；DNA单链断裂
中图分类号： O571.32+3；R730.55         文献标志码：A     DOI：10.3969/j.issn.1007-7146.2026.01.004

Abstract: To investigate the early radiochemical processes of γ-ray-induced DNA single-strand breaks (SSB), this study employed the Monte Carlo simulation tool TOPAS and its extended module TOPAS-nBio to construct a water sphere-plasmid microscale simulation model. The model was used to simulate the irradiation of supercoiled pUC19 plasmids by 60Coγ-rays in an aqueous environment and the subsequent induction of SSB in plasmid DNA. The study quantitatively compared the SSB yield under systematically varied conditions of radiation dose, DNA concentration, and hydroxyl radical (·OH) scavenger concentration. The simulation results showed that the SSB yield increased with the elevation of radiation dose. A higher DNA concentration in the environment led to an approximately linear increase in the absolute SSB yield, while the damage efficiency per unit mass of DNA decreased with increasing concentration. An increase in the concentration of ·OH scavengers significantly reduced the SSB yield, indicating that the ·OH scavenging capacity exerts a marked inhibitory effect on SSB formation. The findings of this study provide certain theoretical support for the optimization of radiotherapy, the formulation of radiation protection strategies, and the health risk assessment of nuclear environments.
Key words: gamma ray; plasmid DNA; free radical; Monte Carlo simulation; DNA single strand break
（Acta Laser Biology Sinica, 2026, 35(1): 028-034）