Nanodosimetric quantities and RBE of a clinically relevant carbon-ion beam
Nanodosimetric quantities and RBE of a clinically relevant carbon-ion beam
复制标题
临床相关碳离子束的纳剂量量和 RBE
DOI：
10.1002/mp.13914
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发表时间：
2019-11-28
期刊：
影响因子：
3.8
通讯作者：
Zhang, Xiaofang
中科院分区：
文献类型：
--
作者：
Dai, Tianyuan;Li, Qiang;Zhang, Xiaofang
目的：尽管碳离子治疗在肿瘤治疗中越来越受到重视，但治疗用碳离子束在组织中形成的电离模式还没有得到充分的研究。在这项工作中，首次对临床相关的碳离子束的纳米剂量和相对生物效应(RBE)进行了系统的计算。方法采用径迹结构和凝聚历史蒙特卡罗(MC)模拟相结合的方法计算纳米剂量量。通过MC模拟，在水中产生了临床上相关的碳离子铅笔束辐射场不同位置的碎片和能谱。然后基于光谱和通过轨道结构MC模拟创建的预先计算的纳米剂量数据库，获得这些位置的纳米碘量，例如平均电离团簇大小(M1)、条件团簇大小的第一矩(M1C2)、累积概率(F2)和条件累积概率(F3C2)。此外，还介绍了一种基于所述纳米剂量量计算RBE的新方法。然后对不同水当量深度的碳离子束进行了径向电子能量计算。结果获得了不同水当量深度的纳米剂量和RBE值的横向分布。M_1、M_1C_2、F_2和F_3C_2在波束中心线的平台处分别为1.49、2.67、0.30和0.38，在布拉格峰周围深度处分别达到最大值2.79、5.69、0.47和0.68。在一定深度下，M_1和F_2随距离中轴的增加而横向减小，而M_1C2和F_3C_2除了布拉格峰上升沿的M_1C_2外，几乎没有变化，而后减小。计算的RBE值在平台处为1.07，在Bragg峰附近为3.13。计算的RBE值与实验数据吻合较好。结论不同的纳米剂量以不同的方式表征治疗性碳离子束的径迹结构。由碳离子束产生的详细电离图案可以用纳米剂量量来表征。此外，本文所采用的计算纳米剂量量的组合方法不仅有效，而且方便。纳米碘量对碳离子治疗中的RBE计算有很大的帮助。
Purpose Although carbon-ion therapy is becoming increasingly attractive to the treatment of tumors, details about the ionization pattern formed by therapeutic carbon-ion beam in tissue have not been fully investigated. In this work, systematic calculations for the nanodosimetric quantities and relative biological effectiveness (RBE) of a clinically relevant carbon-ion beam were studied for the first time. Methods The method combining both track structure and condensed history Monte Carlo (MC) simulations was adopted to calculate the nanodosimetric quantities. Fragments and energy spectra at different positions of the radiation field of a clinically relevant carbon-ion pencil beam were generated by means of MC simulations in water. Nanodosimetric quantities such as mean ionization cluster size (M1), the first moment of conditional cluster size (M1C2), cumulative probability (F2), and conditional cumulative probability (F3C2) at these positions were then acquired based on the spectra and the pre-calculated nanodosimetric database created by track structure MC simulations. What's more, a novel approach to calculate RBE based on the said nanodosimetric quantities was introduced. The RBE calculations were then conducted for the carbon-ion beam at different water-equivalent depths. Results Lateral distributions at various water-equivalent depths of both the nanodosimetric quantities and RBE values were obtained. The values of M1, M1C2, F2, and F3C2 were 1.49, 2.67, 0.30, and 0.38 at the plateau at the beam central axis and maximized at 2.79, 5.69, 0.47, and 0.68 at the depths around the Bragg peak, respectively. At a given depth, M1 and F2 decreased laterally with increasing the distance to the beam central axis while M1C2 and F3C2 remained nearly unchanged at first and then decreased except for M1C2 at the rising edge of the Bragg peak. The calculated RBE values were 1.07 at the plateau and 3.13 around the Bragg peak. Good agreement between the calculated RBE values and experimental data was obtained. Conclusions Different nanodosimetric quantities feature the track structure of therapeutic carbon-ion beam in different manners. Detailed ionization patterns generated by carbon-ion beam could be characterized by nanodosimetric quantities. Moreover the combined method adopted in this work to calculate nanodosimetric quantities is not only valid but also convenient. Nanodosimetric quantities are significantly helpful for the RBE calculations in carbon-ion therapy.