Abstarct: Treatment for Boron Neutron Capture Therapy (BNCT) is a new method for treating malignant tumors. This treatment is baxsed on the reaction 10B(n,a)7Li . Its products are high-energy alpha and lithium particles with a short-range and high linear energy transfer (LET), so they put all their energy in the tumor and destroy the cancer cells. In this study, the proton-lithium reaction has been used as a neutron source in BNCT. Our goal is to design an appropriate Beam Shaping Assembly (BSA) for this source and to achieve the maximum thermal neutron flux with the lowest contamination caused by fast and gamma neutrons. The neutron flux output must meet all the standards of the international agency. Since the cross-section of the proton-lithium reaction does not exist in the MCNPX2.6 code, this reaction is simulated in LISE ++ code. Gamma obtained from this code, for a current of 10 mA, the proton is simulated with the BSA selective design in the MCNP code to calculate gamma dosage. To calculate the dose, a phantom of the body's equivalent body should be used. Here is a 6-centimeter water sphere, considered as phantom.