Wakabayashi Genichiro, Nohtomi Akihiro, Yahiro Eriko, Fujibuchi Toshioh, Fukunaga Junichi, Umezu Yoshiyuki, Nakamura Yasuhiko, Nakamura Katsumasa, Hosono Makoto, Itoh Tetsuo
Atomic Energy Research Institute, Kinki University, 3-4-1 Kowakae, Higashiosaka-shi, Osaka, 577-8502, Japan,
Radiol Phys Technol. 2015 Jan;8(1):125-34. doi: 10.1007/s12194-014-0300-3. Epub 2014 Nov 18.
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.
对碘化钠（NaI）闪烁体活化用于临床直线加速器中子监测的适用性进行了实验研究。热中子注量率是通过测量中子辐照碘化钠闪烁体中产生的碘-128活度得出的；碘-128发射的β射线能被碘化钠闪烁体有效探测到。为验证该中子测量方法的有效性，我们在研究堆对碘化钠闪烁体进行辐照，并估算了中子注量率。然后将该方法应用于10兆伏直线加速器（瓦里安Clinac 21EX）的中子测量，在等中心处以及距等中心30厘米处估算了中子注量率。当闪烁体直接受到高能X射线辐照时，除了产生碘-128和钠-24外，还观察到由于光核反应生成了碘-126。从这些测量结果发现，通过活化碘化钠闪烁体进行中子测量在利用短时间辐照后的快速测量来估算低中子注量率方面具有很大优势。此外，还讨论了该方法未来在放射治疗设施患者治疗期间对中子进行准实时监测的应用，以及中子剂量的评估方法。
