Investigation of photoneutron production by Siemens artiste linac: A Monte Carlo Study

Abstract

In radiotherapy with electron or photon beams, if the produced photon energy is higher than ~7 MeV, neutrons may be produced through photoneutron interaction, exposing not only the patient but the personnel outside the room, by passing through the walls or skyshine. This exposure to photoneutron induced doses can be detrimental to people's health.In this study, deposited energy and fluences at different points inside and outside the room have been examined by the MCNP code for a Siemens Artiste in a bunker. Different thicknesses of the roof have been investigated for examining the skyshine. In addition, two layouts of room door were compared in term of ambient dose equivalent (ADE) leakage. The deposited energy and fluence distributions were obtained in the head of linac and the bunker.In the main hall of the room the fast neutrons were prevailing, but within the maze and at the corners, the neutron spectrum has been shifted into thermal and epithermal neutrons (<10 keV). In addition, the peak of the neutron spectrum in front of the head of the linac was about 0.5–1.0 MeV. The optimum thickness of the roof was 1 m to reduce skyshine ADE to an acceptable value. The dominant neutrons inside the room were the fast neutrons. In term of ADE, in the outside of the doors, the priority was to lateral door layout.The findings had a good coincidence with literatures, despite the differences in the room size and linacs models. These characteristics make also possible to calculate the deposited energy distribution and particle spectra for other settings. In addition, the optimum roof thickness calculating can lead to economic and practical effectiveness.