Monte Carlo Optimization And Design Of Beam Shaping Assembly For Multi-terminal BNCT Facility Based On Accelerator

Boron Neutron Capture Therapy（BNCT）is an innovative and accurate radiation therapy.It is based on the capture reaction between thermal neutrons and ¹⁰B.After capturing thermal neutrons,¹⁰B fissions intoαparticles and ⁷Li which have short ranges and high energy,and tumor cells will be accurately destroyed.The Accelerator-Based BNCT（AB-BNCT）is distinguished by low cost,high safety,and easy generation of neutrons suitable for BNCT.Beam Shaping Assembly（BSA）is a vital part of the AB-BNCT facility.The role of BSA is to moderate the high-energy neutrons generated by the accelerator to thermal or epithermal neutrons,and to gain enough flux while minimizing undesired components,like fast neutrons,andγrays.In this paper,we use the Monte Carlo method to design BSAs that can moderate the fast neutron generated by a 2.5 Me V/30 m A proton accelerator to the thermal（<0.5 e V）and the epithermal（0.5 e V-10 ke V）neutron apply for multi-terminal BNCT facility.The design of BSA and materials that commonly used for the moderator,reflector,and filter were firstly determined.Then the materials and dimensions of each components are evaluated separately to find the optimal choices.The parameters of neutron beam for BNCT that recommended by the International Atomic Energy Agency（IAEA）are used as the optimization criteria.Finally,the BSAs that can generate thermal and epithermal neutron beam for multi-terminal BNCT were obtained.The results show that the parameters of the thermal and epithermal neutron beams are all meet the recommended values of IAEA.The thermal and epithermal neutron flux reach 1.82×10⁹and 1.26×10⁹(cm^-2s^-1).In addition,the clinical parameters of the neutron beam in the homogeneous phantom were calculated.Advantage depths of thermal and epithermal neutron beam reach 3.52and 7.93cm,respectively.The therapy ratios at advantage depth are 4.56 and 3.83,respectively.It is proved that thermal epithermal neutron beam can meet the requirements of clinical treatment,and obtain high therapeutic gain.