Boron Neutron Capture Therapy (bnct) Monte Carlo Simulation

The process of the particle transportation in brain is introduced in this thesis. It is simulated by a general Monte Carlo code MCNP. Some differences in lower energy region are existed between deterministic result and Monte Carlo result. We analyse the reason and guess the difference is from the treatment of neutron thermalization. Due to a detail physics treatment of MCNP code in thermalization, we think the MCNP result more credibility. On the other hand, an approximate estimation about transport cross-section is given for obtaining the dose. Compared with the deterministic method, the validity of Monte Carlo method has been proved in simulation of Boron Neutron Capture Therapy.The absorbed dose rates, which adopt different fix size mesh, such as 4mm, 8mm and 16mm, are simulated for an ellipsoid model. For 16mm model, the calculated time can be accepted, but the result precision is not enough to satisfy our demand. For 8mm model, there also exists some shortage similar with 16mm model. For 4mm model, the result is good, but its cost is too high in memory and computation time. So we develop a combination mesh model. It is a combination of the three different mesh sizes according to the depth of particle penetrated. The good result is obtained. At the same precision as 4mm model, the number of cells is only one third of 4mm model and the computational time is less 63% than it of 4mm model.