Contents lists available at ScienceDirect Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso Monte Carlo study of neutron-ambient dose equivalent to patient in treatment room A. Mohammadi a , H. Afarideh a , F. Abbasi Davani b , M. Ghergherehchi c, ⁎ , A. Arbabi d a Energy Engineering and Physics Department, Amir Kabir University of Technology, Tehran, Iran b Radiation Application Group, Shahid Beheshti University, Tehran, Iran c College of Information & Communication Engineering, School of Electronics and Electrical Engineering, Sungkyunkwan University, Suwon, Republic of Korea d Department of Medical Physics, Imam Hosein Hospital, Shahid Beheshti Medical University, Tehran, Iran ARTICLE INFO Keywords: Scattering factor Thermal factor Medical linear accelerator Treatment room ABSTRACT This paper presents an analytical method for the calculation of the neutron ambient dose equivalent H* (10) regarding patients, whereby the different concrete types that are used in the surrounding walls of the treatment room are considered. This work has been performed according to a detailed simulation of the Varian 2300C/D linear accelerator head that is operated at 18 MV, and silver activation counter as a neutron detector, for which the Monte Carlo MCNPX 2.6 code is used, with and without the treatment room walls. The results show that, when compared to the neutrons that leak from the LINAC, both the scattered and thermal neutrons are the major factors that comprise the out-of field neutron dose. The scattering factors for the limonite-steel, magnetite-steel, and ordinary concretes have been calculated as 0.91 ± 0.09, 1.08 ± 0.10, and 0.371 ± 0.01, respectively, while the corresponding thermal factors are 34.22 ± 3.84, 23.44 ± 1.62, and 52.28 ± 1.99, respectively (both the scattering and thermal factors are for the isocenter region); moreover, the treatment room is composed of magnetite-steel and limonite-steel concretes, so the neutron doses to the patient are 1.79 times and 1.62 times greater than that from an ordinary concrete composition. The results also confirm that the scattering and thermal factors do not depend on the details of the chosen linear accelerator head model. It is anticipated that the results of the present work will be of great interest to the manufacturers of medical linear accelerators. 1. Introduction Medical linear accelerators of different models and electron en- ergies (4–25 MeV) are widely used for radiotherapy. For radiation protection purposes, these devices are normally installed in treatment rooms that are composed of particular dimensions and are constructed with the use of different concrete types. The unwanted neutrons are produced through the electronuclear (e,én), single photonuclear (γ,n), and double photonuclear (γ,2n) reactions of the high-energy electrons and photons that bombard the high-Z material targets when the energy of the photon beam is greater than approximately 7 MeV (Hsu et al., 2010; Mesbahi et al., 2010; Naseri and Mesbahi, 2010; Thalhofer et al., 2014). The produced neutrons basically lose their initial energies through the multiple scatterings that are from the different elements of the treatment room walls, and they are then scattered back to the treatment room where they may reach the patient. The scattered photons and neutrons from the treatment room are the main dosage sources in the out-of field region (Biltekin et al., 2015; Followill et al., 2003; Liu et al., 2011; Takam, 2010; Vega-Carrillo et al., 2007; Xu et al., 2008). The measurement and applied correction factor of the scattered radiation contribution are recommended by the IAEA for all of the reference radiations at certain distances. The basic sources of scattered radiations are the walls, floor, and ceiling, as well as the other objects that normally exist in the treatment room, and the use of the shadow cone is one of the recommended methods for the measurement of the scattered neutrons in the irradiation room (IAEA, 2000a, 200b; ISO8529, 1998). The quality of radiation therapy is highly dependent on the photon doses that are delivered to the patient. In general, the delivered dose is due to the direct and scattered radiations in the treatment room (Bartesaghi, 2007); for example, the emphasis of both the Safety Series Report No.16 (2000) and the ISO8529–3 (2000) is a maximal elimination of the scattered neutrons for the neutron dosi- meters and the field calibration, and this is also confirmed for the calibration of the gamma dosimeters. With regard to radiotherapy patients, the ICRP publication 103 (ICRP, 2007) calls for “… delivery of the required dose to the volume to be treated, avoiding unnecessary http://dx.doi.org/10.1016/j.apradiso.2016.07.009 Received 12 April 2016; Received in revised form 5 July 2016; Accepted 11 July 2016 ⁎ Corresponding author. E-mail addresses: hafarideh@aut.ac.ir (H. Afarideh), mitragh@skku.edu (M. Ghergherehchi). Applied Radiation and Isotopes 118 (2016) 140–148 0969-8043/ © 2016 Published by Elsevier Ltd. Available online 12 July 2016 crossmark