Absorbed dose estimates to structures of the brain and head using a high‐resolution voxel‐based head phantom

The purpose of this article is to demonstrate the viability of using a high‐resolution 3‐D head phantom in Monte Carlo N ‐Particle (MCNP) for boron neutron capture therapy (BNCT) structure dosimetry. This work describes a high‐resolution voxel‐based model of a human head and its use for calculating absorbed doses to the structures of the brain. The Zubal head phantom is a 3‐D model of a human head that can be displayed and manipulated on a computer. Several changes were made to the original head phantom which now contains over 29 critical structures of the brain and head. The modified phantom is a 85×109×120 lattice of voxels, where each voxel is 2.2×2.2×1.4 mm 3 . This model was translated into MCNP lattice format. As a proof of principle study, two MCNP absorbed dose calculations were made (left and right lateral irradiations) using a uniformly distributed neutron disk source with an 1 / E energy spectrum. Additionally, the results of these two calculations were combined to estimate the absorbed doses from a bilateral irradiation. Radiobiologically equivalent (RBE) doses were calculated for all structures and were normalized to 12.8 Gy‐Eq. For a left lateral irradiation, the left motor cortex receives the limiting RBE dose. For a bilateral irradiation, the insula cortices receive the limiting dose. Among the nonencephalic structures, the parotid glands receive RBE doses that were within 15% of the limiting dose.