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

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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.

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Acknowledgments

This study was performed in part under the Cooperative Research at Kinki University Reactor supported by the Graduate School of Engineering, Osaka University. The authors thank Mr. H. Kinoshita, Ms. A. Takayama, and Mr. S. Honda of the Department of Health Sciences, Kyushu University, as well as Mr. S. Nagamine, and Mr. D. Nakanishi of the Department of Radiology, Kyushu University Hospital, for their cooperation in this study.

Conflict of interest

The authors declare that they have no conflict of interest.

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Authors and Affiliations

  1. Atomic Energy Research Institute, Kinki University, 3-4-1 Kowakae, Higashiosaka-shi, Osaka, 577-8502, Japan

    Genichiro Wakabayashi & Tetsuo Itoh

  2. Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan

    Akihiro Nohtomi, Eriko Yahiro & Toshioh Fujibuchi

  3. Department of Radiology, Kyushu University Hospital, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan

    Junichi Fukunaga, Yoshiyuki Umezu, Yasuhiko Nakamura & Katsumasa Nakamura

  4. Institute of Advanced Clinical Medicine, Kinki University, 377-2 Ohno-Higashi, Osaka-Sayama, 589-8511, Japan

    Makoto Hosono

Authors
  1. Genichiro Wakabayashi
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  2. Akihiro Nohtomi
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  3. Eriko Yahiro
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  4. Toshioh Fujibuchi
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  5. Junichi Fukunaga
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  6. Yoshiyuki Umezu
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  7. Yasuhiko Nakamura
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  8. Katsumasa Nakamura
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  9. Makoto Hosono
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  10. Tetsuo Itoh
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Correspondence to Genichiro Wakabayashi.

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Wakabayashi, G., Nohtomi, A., Yahiro, E. et al. Applicability of self-activation of an NaI scintillator for measurement of photo-neutrons around a high-energy X-ray radiotherapy machine. Radiol Phys Technol 8, 125–134 (2015). https://doi.org/10.1007/s12194-014-0300-3

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  • DOI: https://doi.org/10.1007/s12194-014-0300-3

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