title: Applicability of self-activation of an NaI scintillator for measurement of photo-neutrons around a high-energy X-ray radiotherapy machine.
abstract: The applicability of the activation of an NaI scintillator for neutron monitoring at a clinical linac was investigated experimentally. Thermal neutron fluence rates are derived by measurement of the I-128 activity generated in an NaI scintillator irradiated by neutrons; β-rays from I-128 are detected efficiently by the NaI scintillator. In order to verify the validity of this method for neutron measurement, we irradiated an NaI scintillator at a research reactor, and the neutron fluence rate was estimated. The method was then applied to neutron measurement at a 10-MV linac (Varian Clinac 21EX), and the neutron fluence rate was estimated at the isocenter and at 30 cm from the isocenter. When the scintillator was irradiated directly by high-energy X-rays, the production of I-126 was observed due to photo-nuclear reactions, in addition to the generation of I-128 and Na-24. From the results obtained by these measurements, it was found that the neutron measurement by activation of an NaI scintillator has a great advantage in estimates of a low neutron fluence rate by use of a quick measurement following a short-time irradiation. Also, the future application of this method to quasi real-time monitoring of neutrons during patient treatments at a radiotherapy facility is discussed, as well as the method of evaluation of the neutron dose.
authors.affiliation: Atomic Energy Research Institute, Kinki University, 3-4-1 Kowakae, Higashiosaka-shi, Osaka, 577-8502, Japan, genichiro@kindai.ac.jp.
authors.forename: Genichiro
authors.initials: G
authors.lastname: Wakabayashi
authors.forename: Akihiro
authors.initials: A
authors.lastname: Nohtomi
authors.forename: Eriko
authors.initials: E
authors.lastname: Yahiro
authors.forename: Toshioh
authors.initials: T
authors.lastname: Fujibuchi
authors.forename: Junichi
authors.initials: J
authors.lastname: Fukunaga
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Umezu
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Katsumasa
authors.initials: K
authors.lastname: Nakamura
authors.forename: Makoto
authors.initials: M
authors.lastname: Hosono
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Itoh
mesh_terms: D006801:Humans; D009010:Monte Carlo Method; D009502:Neutrons; D010315:Particle Accelerators; D017785:Photons; D011829:Radiation Dosage; D011882:Radiotherapy, High-Energy / Q000295:instrumentation* / Q000379:methods; D012588:Scintillation Counting / Q000295:instrumentation* / Q000379:methods*; D012974:Sodium Iodide / Q000737:chemistry*; D014965:X-Rays
chemical_list: D012974:Sodium Iodide