Monte Carlo Simulation of Neutron Contamination in High Energy Linac Bunker using TOPAS
Alwali W Solichin (a*), Anisza Okselia (b), Alfia F Azimah (a), Freddy Haryanto (a)

a) Department of Physics, Physics Mathematics and Natural Sciences Faculty, Institut Teknologi Bandung, 40132, Bandung, Indonesia
*lattov[at]outlook.com
b) RSUP Dr. Hasan Sadikin, 40161, Bandung, Indonesia

Abstract

The growing number of radiotherapy centres in Indonesia means a more effective and accurate protection measure needs to be implemented. Neutron contamination is one of the side effects of high-energy photon radiation in radiotherapy treatment using linear accelerators. This preliminary study aims to comprehend the neutron dose distribution inside a high-energy linear accelerator bunker. A monte carlo simulation using TOPAS 3.9 will be utilized to determine the neutron contamination in high energy photon radiation. A Siemens Oncor head LINAC will be simulated to generate two phase-space. The first phase space is commissioned above the jaws, and the second phase space is below the MLC for a 10x10 cm field size in 100 SSD. The second phase space will then be used as the beam source in the bunker. The bunker specifications will conform to the IAEA regulations, SRS 147, and NCRP 51 for LINAC with 10 MV energy. Earlier simulation using 18 MV energy showed that the first phase space originated from 107 particles generated 2 x 108 particles, with 104 neutron contamination. The second phase space originated from the first phase space with five times redistribution and generated 7 x 107 particles with 7 x 104 neutron contamination. These results showed that there are significant number of neutron contamination in high energy LINAC. The dose distribution will then be analyzed using the isodose curve using phase space data using 10 MV energy LINAC, due to the commonly used LINAC in Indonesia is at this energy rate. Furthermore, data from a 10 MV LINAC facility will be obtained and compared. This research will be the preliminary study of neutron radiation dose distribution in high-energy LINAC bunker.

Keywords: Radiotherapy, Neutron Contamination, Monte Carlo, Radiation Protection

Topic: Biophysics and Medical Physics