Abstract

Purpose

Through introducing stochastic quantities that can be connected to the dimensions of the microscopic structures exposed to radiations, microdosimetry is concerned with the substantive specifications of radiation quality that could help gain insight into radiation effects. Utilizing the μ-randomness method and Geant4-DNA code, we calculated microdosimetry quantities for nanometric structures in a spherical body of water irradiated with protons. To gain more insight into the effects of radiation on microscopic structures and validate the code parameters, we made a comparison between our results obtained within Geant4-DNA and results from other simulations.

Materials and methods

We calculated microdosimetric quantities through irradiating a spherical body of water of 6 μm diameter with 0.5–100 MeV protons. Microdosimetric quantities were derived for cylinders with diameter × height values of 23 × 23, 50 × 100, and 300 × 300 Å × Å, which would resemble the typical sizes of sub-cellular organisms such as the DNA, nucleosome, and chromatin fiber. We exploited the concept of μ-randomness to introduce convex bodies of random positions and directions for calculating microdosimetric quantities. We used the Geant4-DNA Monte Carlo simulation toolkit for transporting protons and secondary particles and calculating the frequency- and dose-mean lineal and specific energies in cylindrical volumes. Specifically, for same-sized cylindrical volumes, microdosimetric parameters obtained by Nikjoo et al. using the KURBUC code were used for evaluation.

Results

For the energy range investigated, the frequency-mean lineal energy, dose-mean lineal energy, frequency-mean specific energy, and dose-mean specific energy vary within [2.34,47.06] (keV/μm), [10.40,68.55] (keV/μm), [0.04,39.38] × 10⁶ cGy, and [0.16,90.29] × 10⁶ cGy, respectively. Regardless of the proton energy, our specific-energy results showed higher sensitivity to volume change, for smaller cylinder volumes rather than larger ones. Regardless of both proton energy and volume of the cylinder under study, we observed a generally better agreement between our frequency-mean, than dose-mean, specific energy results and the KURBUC results.

Conclusion

Using Geant4-DNA to account for the stochastic nature of energy depositions due to physical interactions between radiation and matter, we calculated microdosimetry parameters concerning proton irradiation. By employing microdosimetry concepts in conjunction with simulation results of our previous work on radiation effects on the DNA, we pinpointed and quantified correlations between microdosimetry parameters and DNA damage. As such, for a volume with comparable mass and mean chord length to the DNA, we could observe the clear correspondence of the mean lineal and specific energy results with the double-strand-break yields of protons in Gy⁻¹.Gbp⁻¹.

中文翻译：

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使用 Geant4-DNA 和纳米结构的 μ 随机采样算法计算质子的微剂量光谱

摘要

目的

通过引入可以与暴露于辐射的微观结构的尺寸相关联的随机量，微剂量学关注辐射质量的实质性规范，这有助于深入了解辐射效应。利用μ-随机性方法和 Geant4-DNA 代码，我们计算了用质子照射的球形水体中纳米结构的微剂量量。为了更深入地了解辐射对微观结构的影响并验证代码参数，我们将我们在 Geant4-DNA 中获得的结果与其他模拟的结果进行了比较。

材料和方法

我们通过用 0.5-100 MeV 质子照射直径为 6 μm的球形水体来计算微剂量 。微剂量量取自直径 × 高度值为 23 × 23、50 × 100 和 300 × 300 Å × Å 的圆柱体，它们类似于亚细胞生物的典型尺寸，如 DNA、核小体和染色质纤维。我们利用μ的概念-randomness 引入随机位置和方向的凸体以计算微剂量。我们使用 Geant4-DNA Monte Carlo 模拟工具包来传输质子和次级粒子，并计算圆柱形体积中的频率和剂量平均线性和比能。具体来说，对于相同大小的圆柱体，Nikjoo 等人获得的微剂量参数。使用 KURBUC 代码进行评估。

结果

对于能量范围研究中，频率的平均能量线性，剂量平均线性能量，频率均值比能，并且剂量均值比能量内变化[2.34,47.06]（千电子伏/ μ M），[10.40,68.55] (keV/ μ m)、[0.04,39.38] × 10 ⁶  cGy 和 [0.16,90.29] × 10 ⁶  cGy。无论质子能量如何，我们的比能结果对体积变化的敏感性更高，对于较小的圆柱体积而不是较大的圆柱体积。不管所研究的圆柱体的质子能量和体积如何，我们观察到我们的频率平均值比剂量平均值比能量结果与 KURBUC 结果之间的一致性通常更好。

结论

使用 Geant4-DNA 来解释由于辐射和物质之间的物理相互作用引起的能量沉积的随机性质，我们计算了有关质子辐射的微剂量参数。通过将微剂量学概念与我们之前关于辐射对 DNA 影响的工作的模拟结果相结合，我们确定并量化了微剂量学参数与 DNA 损伤之间的相关性。因此，对于质量和平均弦长与 DNA 相当的体积，我们可以观察到平均线性和比能量结果与 Gy ^-1 .Gbp ^-1质子的双链断裂产率之间的明确对应关系。