Hsieh Mindy, Liu Yingzi, Mostafaei Farshad, Poulson Jean M, Nie Linda H
School of Health Sciences, Purdue University, West Lafayette, IN, 47906, USA.
Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, WI, 53226, USA.
Med Phys. 2017 Feb;44(2):637-643. doi: 10.1002/mp.12051.
Boron neutron capture therapy (BNCT) is a binary treatment modality that uses high LET particles to achieve tumor cell killing. Deuterium-deuterium (DD) compact neutron generators have advantages over nuclear reactors and large accelerators as the BNCT neutron source, such as their compact size, low cost, and relatively easy installation. The purpose of this study is to design a beam shaping assembly (BSA) for a DD neutron generator and assess the potential of a DD-based BNCT system using Monte Carlo (MC) simulations.
The MC model consisted of a head phantom, a DD neutron source, and a BSA. The head phantom had tally cylinders along the centerline for computing neutron and photon fluences and calculating the dose as a function of depth. The head phantom was placed at 4 cm from the BSA. The neutron source was modeled to resemble the source of our current DD neutron generator. A BSA was designed to moderate and shape the 2.45-MeV DD neutrons to the epithermal (0.5 eV to 10 keV) range. The BSA had multiple components, including moderator, reflector, collimator, and filter. Various materials and configurations were tested for each component. Each BSA layout was assessed in terms of the in-air and in-phantom parameters. The maximum brain dose was limited to 12.5 Gray-Equivalent (Gy-Eq) and the skin dose to 18 Gy-Eq.
The optimized BSA configuration included 30 cm of lead for reflector, 45 cm of LiF, and 10 cm of MgF for moderator, 10 cm of lead for collimator, and 0.1 mm of cadmium for thermal neutron filter. Epithermal flux at the beam aperture was 1.0 × 10 n /cm -s; thermal-to-epithermal neutron ratio was 0.05; fast neutron dose per epithermal was 5.5 × 10 Gy-cm /φ , and photon dose per epithermal was 2.4 × 10 Gy-cm /φ . The AD, AR, and the advantage depth dose rate were 12.1 cm, 3.7, and 3.2 × 10 cGy-Eq/min, respectively. The maximum skin dose was 0.56 Gy-Eq. The DD neutron yield that is needed to irradiate in reasonable time was 4.9 × 10 n/s.
Results demonstrated that a DD-based BNCT system could be designed to produce neutron beams that have acceptable in-air and in-phantom characteristics. The parameter values were comparable to those of existing BNCT facilities. Continuing efforts are ongoing to improve the DD neutron yield.
硼中子俘获疗法（BNCT）是一种二元治疗方式，利用高传能线密度粒子来杀死肿瘤细胞。氘 - 氘（DD）紧凑型中子发生器作为BNCT中子源，相较于核反应堆和大型加速器具有诸多优势，比如尺寸紧凑、成本低廉以及安装相对简便。本研究的目的是为DD中子发生器设计一个束流整形组件（BSA），并使用蒙特卡罗（MC）模拟评估基于DD的BNCT系统的潜力。
MC模型由头部体模、DD中子源和一个BSA组成。头部体模沿中心线设有计数圆筒，用于计算中子和光子注量，并计算作为深度函数的剂量。头部体模放置在距BSA 4厘米处。中子源的建模类似于我们当前的DD中子发生器的源。设计了一个BSA，用于将2.45兆电子伏的DD中子慢化并整形到超热（0.5电子伏至10千电子伏）范围。该BSA有多个组件，包括慢化剂、反射器、准直器和滤波器。对每个组件测试了各种材料和配置。根据空气中和体模内参数评估每个BSA布局。最大脑剂量限制为12.5格雷当量（Gy - Eq），皮肤剂量限制为18 Gy - Eq。
优化后的BSA配置包括用于反射器的30厘米铅、用于慢化剂的45厘米LiF和10厘米MgF、用于准直器的10厘米铅以及用于热中子滤波器的0.1毫米镉。束流孔径处的超热通量为1.0×10⁹ n/cm² - s；热中子与超热中子之比为0.05；每个超热中子的快中子剂量为5.5×10⁻⁴ Gy - cm² /φ，每个超热中子的光子剂量为2.4×10⁻⁴ Gy - cm² /φ。AD、AR和优势深度剂量率分别为12.1厘米、3.7和3.2×10⁻² cGy - Eq/min。最大皮肤剂量为0.56 Gy - Eq。在合理时间内进行辐照所需的DD中子产额为4.9×10⁹ n/s。
结果表明，可以设计一个基于DD的BNCT系统，以产生具有可接受的空气中和体模内特性的中子束。这些参数值与现有BNCT设施的参数值相当。正在持续努力提高DD中子产额。
