Evaluation of absorbed effective dose and treatment conditions for a brain tumor outside of the head phantom center in treatment by Boron Neutron Capture Therapy Using Monte Carlo Simulation

In the field of the treatment of brain toumors by Boron Neutron Capture Therapy, the dose amounts of the neutron components and gamma, and also treatment conditions for a brain tumor out of the head phantom center were simulated. The objectives of this study were to calculate the effective dose and the received dose in a head phantom and determine the duration of treatment, according to the extent permitted by the ICRP commission.
In this research, a human head phantom in front of a neutron system (including 252Cf source, moderator, refelector and neutron and photon filters) was simulated. A spherical-shaped tumor was considered outside of the phantom center. The head phantom consists of three parts of the skin, skull and brain. The simulation was done by the MCNPX 2.6.0 computational code. In this simulation, the tumor with a radius of 1.5 cm at a depth of 2 cm inside the brain was considered.
Tumor treatment was investigated with different boron concentrations in the head phantom. The maximum dose is approximately 0.055 Sv/hr, and is related to the conditions that Boron is not absorbed in healthy tissue. The absorbed dose amount of the epithermal neutrons, under the conditions that Boron is not absorbed in healthy tissue, at the entrance of the skull and in brain tissue extremily drops, and gradually decreases.
The calculations showed when a patient receives radiation about 5 minutes, the received dose equals approximately 4.6 mSv.Under these treatment conditions, the whole body equivalent dose does not exceed 5 mSv per year.