基于纳米的医用直线加速器辐射治疗中快中子屏蔽材料的设计与制作。
Design and fabrication of a Nano-based neutron shield for fast neutrons from medical linear accelerators in radiation therapy.
机构信息
Department of Medical Physics, Faculty of Medicine, Urmia University of Medical Sciences, Urmia, Iran.
Molecular Medicine Research Center, Tabriz University of Medical Sciences, Tabriz, Iran.
出版信息
Radiat Oncol. 2020 May 11;15(1):105. doi: 10.1186/s13014-020-01551-1.
BACKGROUND
Photo-neutrons are produced at the head of the medical linear accelerators (linac) by the interaction of high-energy photons, and patients receive a whole-body-absorbed dose from these neutrons. The current study aimed to find an efficient shielding material for fast neutrons.
METHODS
Nanoparticles (NPs) of FeO and BC were applied in a matrix of silicone resin to design a proper shield against fast neutrons produced by the 18 MeV photon beam of a Varian 2100 C/D linac. Neutron macroscopic cross-sections for three types of samples were calculated by the Monte Carlo (MC) method and experimentally measured for neutrons of an Am-Be source. The designed shields in different concentrations were tested by MCNPX MC code, and the proper concentration was chosen for the experimental test. A shield was designed with two layers, including nano-iron oxide and a layer of nano-boron carbide for eliminating fast neutrons.
RESULTS
MC simulation results with uncertainty less than 1% showed that for discrete energies and 50% nanomaterial concentration, the macroscopic cross-sections for iron oxide and boron carbide at the energy of 1 MeV were 0.36 cm and 0.32 cm, respectively. For 30% nanomaterial concentration, the calculated macroscopic cross-sections for iron oxide and boron carbide shields for Am-Be spectrum equaled 0.12 cm and 0.15 cm, respectively, while they are 0.15 cm and 0.18 cm for the linac spectrum. In the experiment with the Am-Be spectrum, the macroscopic cross-sections for 30% nanomaterial concentration were 0.17 ± 0.01 cm for iron oxide and 0.21 ± 0.02 cm for boron carbide. The measured transmission factors for 30% nanomaterial concentration with the Am-Be spectrum were 0.71 ± 0.01, 0.66 ± 0.02, and 0.62 ± 0.01 for the iron oxide, boron carbide, and double-layer shields, respectively. In addition, these values were 0.74, 0.69, and 0.67, respectively, for MC simulation for the linac spectrum at the same concentration and thickness of 2 cm.
CONCLUSION
Results achieved from MC simulation and experimental tests were in a satisfactory agreement. The difference between MC and measurements was in the range of 10%. Our results demonstrated that the designed double-layer shield has a superior macroscopic cross-section compared with two single-layer nanoshields and more efficiently eliminates fast photo-neutrons.
背景
医学直线加速器（linac）头部的高能光子会产生光中子，患者会受到全身吸收剂量的照射。本研究旨在寻找一种有效的快中子屏蔽材料。
方法
将 FeO 和 BC 纳米颗粒应用于硅树脂基质中，设计一种合适的屏蔽体，以屏蔽由瓦里安 2100 C/D linac 的 18 MeV 光子束产生的快中子。利用蒙特卡罗（MC）方法计算了三种样品的中子宏观截面，并利用 Am-Be 源进行了实验测量。用 MCNPX MC 代码对不同浓度的设计屏蔽体进行了测试，并选择了合适的浓度进行实验测试。设计了一种双层屏蔽体，包括纳米氧化铁和一层纳米碳化硼，以消除快中子。
结果
MC 模拟结果的不确定性小于 1%，表明对于离散能量和 50%纳米材料浓度，在 1 MeV 能量下，氧化铁和碳化硼的宏观截面分别为 0.36 cm 和 0.32 cm。对于 30%纳米材料浓度，计算得到的 Am-Be 能谱下铁氧体和碳化硼屏蔽体的宏观截面分别为 0.12 cm 和 0.15 cm，而 linac 能谱下的宏观截面分别为 0.15 cm 和 0.18 cm。在 Am-Be 能谱的实验中，30%纳米材料浓度下的氧化铁宏观截面为 0.17±0.01 cm，碳化硼的宏观截面为 0.21±0.02 cm。用 Am-Be 能谱测量的 30%纳米材料浓度的透射因子分别为 0.71±0.01、0.66±0.02 和 0.62±0.01，对于铁氧体、碳化硼和双层屏蔽体。此外，在相同浓度和 2 cm 厚度下，MC 模拟的结果分别为 0.74、0.69 和 0.67，用于 linac 能谱。
结论
MC 模拟和实验测试的结果吻合较好。MC 与测量值的差异在 10%范围内。我们的结果表明，设计的双层屏蔽体具有比两个单层纳米屏蔽体更高的宏观截面，能更有效地消除快光中子。
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