Department of Nuclear Medicine and Radiobiology, University of Sherbrooke, Sherbrooke, QC, Canada.
Department of Nuclear Medicine and Radiobiology, University of Sherbrooke, Sherbrooke, QC, Canada.
Z Med Phys. 2023 Nov;33(4):489-498. doi: 10.1016/j.zemedi.2022.07.003. Epub 2022 Aug 13.
In radiotherapy, X-ray or heavy ion beams target tumors to cause damage to their cell DNA. This damage is mainly induced by secondary low energy electrons. In this paper, we report the DNA molecular breaks at the atomic level as a function of electron energy and types of electron interactions using of Monte Carlo simulation. The number of DNA single and double strand breaks are compared to those from experimental results based on electron energies. In recent years, DNA atomistic models were introduced but still the simulations consider energy deposition in volumes of DNA or water equivalent material. We simulated a model of atomistic B-DNA in vacuum, forming 1122 base pairs of 30 nm in length. Each atom has been represented by a sphere whose radius equals the radius of van der Waals. We repeatedly simulated 10 million electrons for each energy from 4 eV to 500 eV and counted each interaction type with its position x, y, z in the volume of DNA. Based on the number and types of interactions at the atomic level, the number of DNA single and double strand breaks were calculated. We found that the dissociative electron attachment has the dominant effect on DNA strand breaks at energies below 10 eV compared to excitation and ionization. In addition, it is straightforward with our simulation to discriminate the strand and base breaks as a function of radiation interaction type and energy. In conclusion, the knowledge of DNA damage at the atomic level helps design direct internal therapeutic agents of cancer treatment.
在放射治疗中，X 射线或重离子束靶向肿瘤，以破坏其细胞 DNA。这种损伤主要是由次级低能电子引起的。本文采用蒙特卡罗模拟方法，报道了电子能量和电子相互作用类型与 DNA 分子断裂的原子水平关系。将单链和双链 DNA 断裂的数量与基于电子能量的实验结果进行了比较。近年来，已经引入了 DNA 原子模型，但模拟仍然考虑 DNA 或水等效材料体积中的能量沉积。我们在真空中模拟了原子 B-DNA 模型，形成了 1122 个碱基对，长度为 30nm。每个原子都用一个球体表示，其半径等于范德华半径。我们为每个从 4eV 到 500eV 的能量重复模拟了 1000 万个电子，并在 DNA 体积内记录了每种相互作用类型的位置 x、y、z。基于原子水平的相互作用数量和类型，计算了单链和双链 DNA 的断裂数量。我们发现，与激发和电离相比，在低于 10eV 的能量下，电子的离解电子俘获对 DNA 链断裂有主导作用。此外，通过我们的模拟，很容易根据辐射相互作用类型和能量来区分链和碱基的断裂。总之，对原子水平 DNA 损伤的了解有助于设计癌症治疗的直接内部治疗剂。
