دانلود رایگان مقاله لاتین مونت کارلو معادل دوز نوترون محیط به بیمار در اتاق درمان از سایت الزویر
عنوان فارسی مقاله:
مطالعه مونت کارلو معادل دوز نوترون محیط به بیمار در اتاق درمان
عنوان انگلیسی مقاله:
Monte Carlo study of neutron-ambient dose equivalent to patient in treatment room
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Monte Carlo study of Medical linear accelerators of different models and electron energies (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 dosimeters 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-ambient dose equivalent to patient in treatment room exposure of healthy tissues.” As described by Pena et al., 2005 the three energy ranges of the neutrons in the treatment room are as follows: Fast neutrons (0.1 MeV to 10 MeV), epithermal neutrons (0.50 MeV to 0.1 MeV), and thermal neutrons (less than 0.50 eV). The three ranges are produced via the interactions between the high energy photons with the LINAC head components and the treatment room walls (Pena et al., 2005). In medical linear accelerators, bremsstrahlung X-rays are produced through the interaction of the high-energy electrons with the target. The scattering and thermal neutron cross sections, the different (γ,n) threshold energies of the materials in the walls, and the linear accelerator installations along the photon path are the most important factors for the determination of the scattering and thermal factors. The unwanted doses of the extra neutrons and photons are not prescribed, as they are of course non-therapeutic; also, the energy spectrum of the produced neutrons ranges from thermal to several MeVs, based on the initial energy of the electron beam (up to 25 MeV). In the treatment room, the average energy of the produced neutrons varies from 0.1 MeV to 2 MeV, and the radiation weighting factor of 20 is recommended for these deeply penetrating particles with a high radiobiological effectiveness (RBE) (NCRP Report 116., 1993); for this reason, their contributions to a patient's out-of field dose that is relative to the direct dose from the photon beam can be important with respect to the risk of cancer inducement (Naseri and Mesbahi, 2010).
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