Abstarct: Boron neutron capture therapy (BNCT) is a method for many kind of tumors that baxsed on (_^10)B(n,α)(_^7)Li reaction. In this method boron carrier localize in tumor and then exposure by epithermal neutron radiation. Epithermal neutrons will lose their energies by interaction with skin, skull and brain tissues then convert to thermal neutrons. Hence when thermal neutrons interact with Boron the reaction will be occurred. The particles which produced by this reaction have short range and cause to destroy the tumor cells. For arising this reaction one need a epithermal neutron source with sufficient intensity. The neutron source in this study is D-T reaction that the produced neutron have 14.1 MeV energy. For achieving epithermal neutron, it need a beam shaping assembly to provide a neutron beam with recommended intensity and quality according to IAEA criteria; this facility named BSA. For computing dose in this study, Snyder phantom is used. All calculation is used by Monte Carlo simulation code MCNP5. The ratio of concentration of boron in tumor and healthy tissue is considered 13:55. After simulation advantage depth, therapeutic depth and treatment time are obtained respectively 10.8 cm, 8.4 cm and 28.19 min.