Monte Carlo simulations were carried out to calculate optimum design parameters of an accelerator based Beam Shaping Assembly
(BSA) for Boron Neutron Capture Therapy (BNCT) of Brain Cancer setup. Epithermal beam of neutrons were obtained through moderation
fast neutrons from 7Li(p,n) reaction in a high density polyethylene moderator and a graphite reflector. The dimensions of the moderator and the
reflector were optimized through optimization of epithermal/fast neutron intensity ratio as a function of geometric parameters
of the setup. Results of our calculation showed the capability of our setup to treat the tumor within 4 cm of the head surface.
The calculated Peak Therapeutic Ratio for the setup was found to be 2.15. With further improvement in the polyethylene moderator
design and brain phantom irradiation-arrangement, the setup capabilities can be improved to reach further deep-seated tumor.