基于氘氚中子源硼中子俘获治疗的中子慢化整形研究

Design of beam shaping assembly for boron neutron capture therapy based on D-T neutron source

硼中子俘获治疗(Boron Neutron Capture Therapy,BNCT)是一种具有广阔前景的癌症治疗方法。氘氚中子源是未来可供选择的BNCT中子源之一,由于氘氚中子源产生的中子能量为14.1 MeV,不能直接用于BNCT,需要进行束流慢化整形。使用蒙特卡罗模拟程序MCNP5设计了相应的束流整形组件(Beam Shaping Assembly,BSA),模拟验证了用半径为14 cm的天然铀球做中子倍增层的优越性,计算结果表明:采用50 cm厚的BiF3和10 cm厚的TiF3组合慢化层,17 cm厚的AlF3补充慢化层,0.2 mm厚的Cd热中子吸收层,3.5 cm厚的Pb作为γ屏蔽层,以及10 cm厚的Pb反射层,获得了较为理想的治疗中子束,输出中子束的空气端参数满足国际原子能机构(International Atomic Energy Agency,IAEA)的建议值。

[Background]Boron neutron capture therapy(BNCT)is a promising treatment for cancer.In recent years,D-T neutron source has shown great potential as a suitable neutron source for BNCT.However,the neutron energy produced by a D-T neutron source is 14.1 MeV,which cannot be straightforwardly used in a BNCT,so beam shaping is necessary.[Purpose]This study aims to design beam shaping assembly(BSA)to make the neutron beam of D-T neutron source suitable for BNCT.[Methods]The Monte Carlo simulation program MCNP5 was employed to design the corresponding BSA for D-T neutron source.The advantages of using natural uranium as neutron multiplicative layer was firstly verified by simulation.Then,the moderating layer was simulated together the supplementary moderating layer,reflective layer,shielding layer and thermal neutron absorption layer using different materials and thickness to obtain optimal configuration of these materials.[Results]Simulation results show that an ideal therapeutic neutron beam is obtained by using a 14 cm radius natural uranium as neutron multiplicative,50 cm thick BiF3 and 10 cm thick Ti F3 as a double-moderating layer,a 17 cm thick AlF3 as a supplementary moderator,a0.2 mm thick Cd as a thermal neutron absorbing layer,a 3.5 cm thick Pb as aγshielding layer and a 10 cm thick Pb as a reflecting layer.Combination of these materials is suggested to optimize and design as the neutron BSA.[Conclusions]The air outlet parameters of output neutron beam using BSA designed in this study can well meet the recommended values of the International Atomic Energy Agency(IAEA).