The invariance of the total direct DNA strand break yield
The invariance of the total direct DNA strand break yield
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DOI：
10.1118/1.3597568
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发表时间：
2011-07-01
期刊：
影响因子：
3.8
通讯作者：
Nieminen, P.
中科院分区：
文献类型：
--
作者：
Bernal, M. A.;deAlmeida, C. E.;Nieminen, P.
目的：前人报道了DNA在不同类型的粒子和能量照射下的总直接断链产额的不变性。本研究旨在解释这种行为的物理原因。方法：使用GEANT4通用蒙特卡罗模拟工具包的GEANT4-DNA扩展被用来确定质子和α粒子对B-DNA几何模型的直接链断裂产额，该模型包括人类遗传物质的五个组织水平。这种粒子在5.225微米深度(感兴趣区域中心附近)的线性能量转移(LET)范围从4.8keV/微米(10 MeV质子)到约235keV/微米(2 MeVα粒子)。在密度为1.06g/cm(3)的液态水均匀介质中，测定了直接总断裂几率、单链断裂几率和双链断裂几率。测量了单链断裂(SSB)能谱、能量沉积事件数和SSB/事件比。结果：发现靶命中概率与入射粒子的类型和能量无关，即使后者是二次电子。这个概率是由系统的几何性质决定的。总的断链产额和达到某一吸收剂量所需的能量沉积事件的次数几乎与入射离子(质子或阿尔法)的类型和能量无关。相反，双链断裂(DSB)产额强烈依赖于入射辐射的LET。结论：单链断裂的产生过程是均匀的，与所涉及的粒子LET无关，至少在本文研究的质子和α粒子能量范围内是这样。目标命中概率仅由目标占据的总体积与辐射储存其能量的ROI之间的比率确定。产生DSB的相邻两个SSB之间的最大间隔距离是打破打靶过程的同质性的参数，使得DSB生产过程具有很强的异质性。(C)2011年美国医学物理学家协会。[DOI：10.1118/1.3597568]
Purpose: The invariance of the total direct strand break yield when DNA is irradiated by different types of particles and energies has been reported by previous works. This study is intended to explain the physical causes of this behavior.Methods: The GEANT4-DNA extension of the GEANT4 general purpose Monte Carlo simulation toolkit has been used to determine direct strand break yields induced by protons and alpha particles impacting on a B-DNA geometrical model, including five organization levels of the human genetic material. The linear energy transfer (LET) of such particles ranges from 4.8 keV/mu m (10 MeV protons) to about 235 keV/mu m (2 MeV alpha particles), at 5.225 mu m depth (near the center of the region of interest). Direct total, single and double strand break probabilities have been determined in a liquid water homogeneous medium with a 1.06 g/cm (3) density. The energetic spectra of single strand breaks (SSB), the number of energy deposition events, and the SSB/event ratio were determined.Results: The target-hit probability was found to be independent of both the type and the energy of the incident particle, even if this latter is a secondary electron. This probability is determined by the geometrical properties of the system. The total strand break yield and the number of energy deposition events required to reach a certain absorbed dose were found nearly independent of the type and energy of the incident ion (proton or alpha). In contrast, the double strand break (DSB) yield was found strongly dependent on the LET of the incident radiation.Conclusions: The SSB generation process is homogeneous and independent of the LET of the particles involved, at least within the proton and alpha particle energy range here studied. The target-hit probability is only determined by the ratio between the total volume occupied by targets and that of the ROI where the radiation deposits its energy. The maximum separation distance between two adjacent SSBs to produce a DSB is the parameter that breaks the homogeneity of the target-hit process, making the DSB production process strongly heterogeneous. (C) 2011 American Association of Physicists in Medicine. [DOI: 10.1118/1.3597568]