AbstractCalculation of physically realistic radiation dose distributions for boron neutron capture therapy (BNCT) is a complex, three-dimensional problem. Traditional one-dimensional (slab) and two-dimensional (cylindrical) models, while useful for neutron beam design and performance analysis, do not provide sufficient accuracy for actual clinical use because the assumed symmetries inherent in such models do not ordinarily exist in the real world. Fortunately, however, it is no longer necessary to make these types of simplifying assumptions. Recent dramatic advances in computing technology have brought full three-dimensional dose distribution calculations for BNCT into the realm of practicality for a wide variety of routine applications. Once a geometric model and the appropriate material compositions have been determined, either stochastic (Monte Carlo) or deterministic calculations of all dose components of interest can now be performed more rapidly and inexpensively for the true three-dimensional geometries typical of actual clinical applications of BNCT.Demonstrations of both Monte Carlo and deterministic techniques for performing three-dimensional dose distribution analysis for BNCT are provided. Calculated results are presented for a three-dimensional Lucite canine-head phantom irradiated in the epithermal neutron beam available at the Brookhaven Medical Research Reactor. The deterministic calculations are performed using the three-dimensional discrete ordinates method. The Monte Carlo calculations employ a novel method for obtaining spatially detailed radiation flux and dose distributions without the use of flux-at-a-point estimators. The calculated results are in good agreement with each other and with thermal neutron flux measurements taken using copper-gold flux wires placed at various locations in the phantom.Three-dimensional dose distribution calculations using both techniques are also presented for the same canine phantom irradiated in the proposed epithermal neutron beam in the Power Burst Facility (PBF) reactor located at the Idaho National Engineering Laboratory. Again, calculated results obtained using the two methods are in good agreement. This exercise allows a direct comparison of the performance of the two epithermal neutron beams for a realistic three-dimensional BNCT application. The PBF beam has a lower level of fast neutron contamination and is much better collimated, resulting in a significantly higher therapeutic ratio (tumor dose relative to normal tissue dose), especially for deep-seated tumor locations.