Evaluation of neutron spectra and dose equivalent from a Varian 2100C/D Medical Linear Accelerator: Monte Carlo simulation and a literature review

In this study was carried out a review according to experimental and Monte Carlo studies in the literature on the neutron production from 18 MV, Varian 2100C/D linac. The effects of these neutrons were investigated on the total fluence, the energy spectra, and the dose equivalent. These factors were calculated as a function of depth and the radiation field size by simulation of linac head using of MCNPX2.6.0 code. The neutron strength was found equal to 1.23 x 10¹² nGy^-1.The results showed that with increasing the field size from 5 x 5 to 40 x 40 cm², the neutron fluence and dose equivalent in the water phantom rose to the maximum value for 25 x 25 cm² field (3.05 x 10⁷ ncm^-2Gy^-1 and 3.14mSvGy^-1 respectively) and then decreased with increasing the field size. According to the results, the magnetite-steel, ordinary, and limonite-steel concrete walls significantly increased the neutron dose equivalent for about 27.4%, 17.2%, and 13.5%, respectively. (authors)