Applicability of self-activation of an NaI scintillator for measurement of photo-neutrons around a high-energy X-ray radiotherapy machine

作     者：Wakabayashi, Genichiro Nohtomi, Akihiro Yahiro, Eriko Fujibuchi, Toshioh Fukunaga, Junichi Umezu, Yoshiyuki Nakamura, Yasuhiko Nakamura, Katsumasa Hosono, Makoto Itoh, Tetsuo 

作者机构：Kinki Univ Atom Energy Res Inst 3-4-1 Kowakae Higashiosaka Osaka 5778502 Japan Kyushu Univ Grad Sch Med Sci Higashi Ku Fukuoka 8128582 Japan Kyushu Univ Hosp Dept Radiol Higashi Ku Fukuoka 8128582 Japan Kinki Univ Inst Adv Clin Med Osaka 5898511 Japan 

出 版 物：《RADIOLOGICAL PHYSICS AND TECHNOLOGY》 (放射线物理和技术)

年 卷 期：2015年第8卷第1期

页      面：125-134页

学科分类：0831[工学-生物医学工程（可授工学、理学、医学学位）] 100207[医学-影像医学与核医学] 1006[医学-中西医结合] 1002[医学-临床医学] 1001[医学-基础医学(可授医学、理学学位)] 08[工学] 1010[医学-医学技术（可授医学、理学学位）] 100106[医学-放射医学] 1009[医学-特种医学] 10[医学] 100602[医学-中西医结合临床] 

基　　金：Graduate School of Engineering  Osaka University 

主　　题：Neutron measurement Clinical linac NaI scintillator I-128 Self-activation method Quasi real-time monitoring 

摘      要：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;beta-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.