ESTIMATION OF NEUTRONS OCCURRING IN THE LINAC ROOM AT DIFFERENT PHOTON ENERGIES

Abstract

The high energy photons produced by the Linear accelerator (Linac) induce some nuclear reactions in the materials in the Linac room and Linac head. Neutrons formed as a result of the interaction of photons with materials are called photoneutrons. The aim of the study is to examine the neutron doses formed in the environment for 6 different photon energies. In the study, the components in the Linac head and the Linac chamber are modeled with the help of the Monte Carlo N-Particle (MCNP) program. Then, the flux and dose of photoneutrons formed at 8 different points as a result of 6 different photon energies obtained from the Linac head were measured. as can be seen from the results, as the photon energy used in the Linac increases, the resulting dose and flux of photoneutron increase. It can be understood from results that the amount of neutron dose to be received by the organs in the treatment field may be higher than the other organs. Especially in the treatments where the patient is lying in the prone position, there may be a possibility of neutrons reaching the patient spinal cord. Since photoneutrons with high radiobiological ability may pose a risk of secondary cancer for patients, the photon energy chosen for patient treatments should be chosen appropriately and the use of unnecessary high photon energy should be avoided.