title: Neutron dose measurements of Varian and Elekta linacs by TLD600 and TLD700 dosimeters and comparison with MCNP calculations.
abstract: High-energy linacs produce secondary particles such as neutrons (photoneutron production). The neutrons have the important role during treatment with high energy photons in terms of protection and dose escalation. In this work, neutron dose equivalents of 18 MV Varian and Elekta accelerators are measured by thermoluminescent dosimeter (TLD) 600 and TLD700 detectors and compared with the Monte Carlo calculations. For neutron and photon dose discrimination, first TLDs were calibrated separately by gamma and neutron doses. Gamma calibration was carried out in two procedures; by standard 60Co source and by 18 MV linac photon beam. For neutron calibration by (241)Am-Be source, irradiations were performed in several different time intervals. The Varian and Elekta linac heads and the phantom were simulated by the MCNPX code (v. 2.5). Neutron dose equivalent was calculated in the central axis, on the phantom surface and depths of 1, 2, 3.3, 4, 5, and 6 cm. The maximum photoneutron dose equivalents which calculated by the MCNPX code were 7.06 and 2.37 mSv.Gy(-1) for Varian and Elekta accelerators, respectively, in comparison with 50 and 44 mSv.Gy(-1) achieved by TLDs. All the results showed more photoneutron production in Varian accelerator compared to Elekta. According to the results, it seems that TLD600 and TLD700 pairs are not suitable dosimeters for neutron dosimetry inside the linac field due to high photon flux, while MCNPX code is an appropriate alternative for studying photoneutron production.
authors.affiliation: Departement of Radiotherapy Oncology, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Hassan Ali
authors.initials: HA
authors.lastname: Nedaie
authors.affiliation: Department of Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.
authors.forename: Hoda
authors.initials: H
authors.lastname: Darestani
authors.affiliation: Department of Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.
authors.forename: Nooshin
authors.initials: N
authors.lastname: Banaee
authors.affiliation: Department of Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran.
authors.forename: Negin
authors.initials: N
authors.lastname: Shagholi
authors.affiliation: Department of Nuclear Engineering, Amirkabir Industrial University, Tehran, Iran.
authors.forename: Kheirollah
authors.initials: K
authors.lastname: Mohammadi
authors.affiliation: Agriculture Medical and Industrial School, Science and Technology Institute, Karaj, Iran.
authors.forename: Arjang
authors.initials: A
authors.lastname: Shahvar
authors.affiliation: Department of Physics, Faculty of Sciences, University of Birjand, Birjand, Iran.
authors.forename: Esmaeel
authors.initials: E
authors.lastname: Bayat
keywords: Elekta; MCNPX code; TLD600; TLD700 varian; neutron dosimetry