| Abstract [eng] |
More than one third of patients with oncological diseases are treated with radiation therapy. During the procedure, patients are irradiated in medical accelerators using high-energy photon, electron or proton fluxes. However interaction of high energy (> 5MeV) particles with radiation shielding constructions of the accelerator may cause generation of neutrons. Due to interaction of neutrons with the shielding constructions radioactive neutron activation products may be formed the influence of which on the radiation doses received by the personnel must be assessed. Monte Carlo-based modeling programs are commonly used to determine neutron flux and related doses. The Monte Carlo N-particle (MCNP) code is probably the most widely used code in the conjunction with ENDF databases. Based on the analysis of literature sources, this work presents a geometric model of a medical linear accelerator "head" and its surrounding environment (radiation therapy room) was developed. Using this geometrical model and Monte Carlo simulation package MCNP6 energy transport calculations related to electron and photon interactions have been performed in the protective structures of the room, 109 particle histories were evaluated for the 16 MeV the electron beam. The range of neutron spectral energies1.1.10-7 -10 MeV calculated in this work corresponds to the results available from the literature sources. However, in contrast to the results of the calculations presented in the literature, the sharp peak in the neutron flux spectrum was not found. This could be due to higher statistical error in the field of ultra-cold and cold neutron energy. The analysis of neutron activation products was performed using the FISPACT-2010 software package and the recommended database EAF-2010. It was found that the following activation products: 183mW, 185mW, 185W, 66Cu, 64Cu, 50Cr, 58Ni are formed in the shielding constructions of the accelerator head and 50Cr 50V 48Ca - in the concrete wall constructions. Calculations showed that the dose rate outside the accelerator head did not exceed 0.01 mSv/h. |
