A comprehensive Monte Carlo study of out-of-field secondary neutron spectra in a scanned-beam proton therapy gantry room
A comprehensive Monte Carlo study of out-of-field secondary neutron spectra in a scanned-beam proton therapy gantry room
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DOI：
10.1016/j.zemedi.2021.01.001
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发表时间：
2021-05-22
影响因子：
2
通讯作者：
Parodi, Katia
中科院分区：
文献类型：
--
作者：
Englbrecht, Franz S.;Trinkl, Sebastian;Parodi, Katia
目的：模拟在扫描质子治疗机架治疗室内体模照射过程中在不同相对位置测量的次级中子辐射场。此外，以确定起源，能量分布，和角发射的二次中子作为质子束energy.Methods的函数：FLUKA蒙特卡罗代码被用来模拟扫描笔形束质子治疗机架，包括屏蔽墙，地板，主要的金属龙门组件，病人表，和一个均匀的PMMA目标的治疗室的相关部分。质子束在水中的实验范围和在空气中的斑点形状的基础上建模。对于来自200 MeV、140 MeV、75 MeV初始质子束的单能11 x 11 cm（2）场以及使用5 cm厚PMMA范围移位器的118 MeV质子，在距等中心2 m处相对于束轴成0度、45度、90度和135度模拟中子能谱。对这四个位置和质子能量的总中子谱进行评分。FLUKA中子能谱模拟与Geant 4模拟进行了交叉检查，使用FLUKA生成的相空间的初始质子束特性。此外，在房间中产生次级中子的房间组件和它们对总spectrum.Results的贡献进行了识别和quantitatively：FLUKA和Geant 4模拟中子谱显示出良好的一般协议与公布的测量在整个模拟中子能量范围为10（-10）至10（3）MeV。与先前的研究一样，来自体模的高能（E >= 19.6 MeV）中子在沿着0度方向上最普遍，而热化（I MeV
Purpose: To simulate secondary neutron radiation fields that had been measured at different relative positions during phantom irradiation inside a scanning proton therapy gantry treatment room. Further, to identify origin, energy distribution, and angular emission of the secondary neutrons as a function of proton beam energy.Methods: The FLUKA Monte Carlo code was used to model the relevant parts of the treatment room in a scanned pencil beam proton therapy gantry including shielding walls, floor, major metallic gantry-components, patient table, and a homogeneous PMMA target. The proton beams were modeled based on experimental beam ranges in water and spot shapes in air. Neutron energy spectra were simulated at 0 degrees, 45 degrees, 90 degrees and 135 degrees relative to the beam axis at 2 m distance from isocenter for monoenergetic 11 x 11 cm(2) fields from 200 Me V, 140 Me V, 75 MeV initial proton beams, as well as for 118 MeV protons with a 5 cm thick PMMA range shifter. The total neutron spectra were scored for these four positions and proton energies. FLUKA neutron spectra simulations were crosschecked with Geant4 simulations using initial proton beam properties from FLUKA-generated phase spaces. Additionally, the room-components generating secondary neutrons in the room and their contributions to the total spectrum were identified and quantified.Results: FLUKA and Geant4 simulated neutron spectra showed good general agreement with published measurements in the whole simulated neutron energy range of 10(-10) to 10(3) MeV. As in previous studies, high-energy (E >= 19.6 MeV) neutrons from the phantom are most prevalent along 0 degrees, while thermalized ( I meV