碳离子在不同材料叶片的多叶光栅上产生的次级粒子研究  

Study on the Secondary Particles Produced in Different Material Leaves of Multi-leaf Collimator under Carbon Ion Irradiation

作　　者：张小芳 孟乾乾 戴中颖[1,2,3,4] 陈卫强 刘新国[1,2,3,4] 李强 ZHANG Xiaofang;MENG Qianqian;DAI Zhongying;CHEN Weiqiang;LIU Xinguo;LI Qiang(Institute of Modern Physics,Chinese Academy of Sciences,Lanzhou 730000,China;Key Laboratory of Heavy Ion Radiation Biology and Medicine of Chinese Academy of Sciences,Lanzhou 730000,China;Key Laboratory of Basic Research on Heavy Ion Radiation Application in Medicine,Gansu Province,Lanzhou 730000,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院近代物理研究所,兰州730000 [2]中国科学院重离子束辐射生物医学重点实验室,兰州730000 [3]甘肃省重离子束辐射医学应用基础重点实验室,兰州730000 [4]中国科学院大学,北京100049

出　　处：《原子核物理评论》2020年第2期217-224,共8页Nuclear Physics Review

基　　金：国家重点研发计划项目资助(2017YFC0108500);国家自然科学基金资助项目(11875299,61631001,U1532264)。

摘　　要：在碳离子放射治疗中,碳离子束与治疗头设备和患者身体相互作用产生的次级粒子可以到达患者体内的许多区域,在产生的次级粒子中以中子和γ射线的产额为最大。在不影响束流配送功能的情况下,减少碳离子放疗中产生的次级中子和γ射线对于降低放疗后出现的正常组织并发症及二次肿瘤风险有着非常重要的意义。本文利用蒙特卡罗(Monte Carlo)方法模拟计算了被动式束流配送系统下,400 MeV/u碳离子束照射到由不同材料叶片构成的多叶光栅(MLC)形成典型的10 cm×10 cm方形射野时,在水模体中产生的次级中子和γ射线所沉积的剂量及空间分布等。模拟结果显示:碳离子束通过MLC形成射野后在水模体中产生的次级中子主要分布在水模体的入射端,次级γ射线较为均匀的分布在整个水模体内,且较多分布在具有展宽Bragg峰(SOBP)射野在水模体中贯穿时的坪区。对于MLC叶片材料的选择,则需根据实际情况对叶片厚度以及次级粒子当量剂量的要求来确定。本文通过模拟研究不同MLC叶片材料产生次级粒子的情况,为被动式束流配送系统中MLC叶片及其他元件的材料选择提供了科学依据。In carbon ion radiotherapy,secondary particles produced through the interaction of carbon ion beam with the treatment head devices and the patient’s body can reach many areas in the patient’s body.Among the secondary particles,the yield of neutrons andγ-rays is largest.Without affecting the beam delivery function,reducing secondary neutrons andγ-rays produced in carbon ion radiotherapy is very important to decrease the normal tissue complications and secondary cancer risk after radiotherapy.In the present work,the Monte Carlo method was used to calculate the dose and spatial distributions of secondary neutrons andγ-rays deposited in water when multi-leaf collimators(MLC)made from different material leaves were adopted to form a typical 10 cm×10 cm square irradiation field for 400 MeV/u carbon ion beam.The simulation results showed that the secondary neutrons produced were mainly distributed at the incident end in the water phantom when the carbon ion beam passed through the MLC,while the secondaryγ-rays were uniformly distributed in the entire water phantom and more dose of the secondaryγ-rays appeared in the plateau when the irradiation field with spread-out Bragg peak(SOBP)travelled in the water phantom.The selection of MLC leaves should be determined according to the actual conditions of MLC leaves thickness and secondary particle equivalent dose requirements.The simulation study presented in this paper provides scientific evidence for the material selection of MLC leaves and other components in carbon ion radiotherapy using passive beam delivery system.

关 键 词：碳离子放射治疗 被动式束流配送系统 次级粒子 剂量分布 蒙特卡罗模拟 

分 类 号：O571.33[理学—粒子物理与原子核物理] Q691.4[理学—物理]