Project 2 Advancement of integrated system for dose estimation in BNCT (R4P2)

概要

I-1.

PROJECT RESEARCHES
Project 2

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PR2

Advancement of integrated system for dose estimation in BNCT

Y. Sakurai
Institute for Integrated Radiation and Nuclear Science,
Kyoto University
BACKGROUNDS AND PURPOSES:
Several types of accelerator-based irradiation system
for boron neutron capture therapy (BNCT) are under development at present. But, there are a number of subjects,
which should be improved for the further advance and
generalization of BNCT.
In the viewpoints of medical physics and engineering,
the advance for dose estimation is one of the important
subjects. For the characterization of irradiation field,
quality assurance and quality control (QA/QC), clinical
irradiation to actual patient, and so on, an ultimate goal is
to perform the three-dimensional and real-time dose estimation in discriminating for thermal, epi-thermal and
fast neutron doses, gamma-ray dose, and boron dose,
with simplicity and low effort. Considering about this
ultimate dose estimation, several kinds of dose estimation
method are studied. It is so difficult to realize the ultimate
dose estimation using only one method, but it is necessary to use simultaneously more than two methods.
The purposes of this project research are the advance
for various dose estimation methods, and the establishment of an integrated system for dose estimation in
BNCT.
In the third year of this research project, 2022, the advancement for the respective dose estimation methods
were forwarded mainly using Heavy Water Neutron Irradiation Facility (HWNIF) and E-3 Neutron Guide Tube
(E-3) at KUR, sequentially the previous year. In addition,
the integrated system was considered for the simultaneous usage of several dose estimation methods
RESEARCH SUBJECTS:
The collaboration and allotted research subjects (ARS)
were organized as follows;
ARS-1 (R4P2-1): Establishment of characterization estimation method in BNCT irradiation field using Bonner sphere and ionization chamber (VI). (Y. Sakurai, A.
Sasaki, N. Matsubayashi, M. Nojiri, D. Fu, T. Takata, H.
Tanaka)
ARS-2 (R4P2-2): Study on neutron energy spectrometry
for epi-thermal neutrons. (S. Yoshihashi, A. Yamazaki,
K. Watanabe, Y. Oshima, A. Uritani, Y. Sakurai)
ARS-3 (R4P2-3): Development of Bonner sphere spectrometer using small lithium-glass scintillator for intense neutron beams. (A. Masuda, T. Matsumoto, S.
Manabe, K. Watanabe, A. Ishikawa, H. Tanaka, Y. Sakurai, H. Harano, T. Takata, A. Uritani)
ARS-4 (R4P2-4): Improvement of the SOF detector system for energy-dependent discrimination and long-term
stability. (M. Ishikawa, S. Ishiguri, K. Takamiya, Y.
Sakurai)

ARS-5 (R4P2-5): Improvement of absolute fast neutron
flux intensity monitor for BNCT. (I. Murata, K. Sagara,
R. Kawahata, S. Tamaki, S. Kusaka, H. Tanaka, Y. Sakurai, T. Takada)
ARS-7 (R4P2-7): Neutron image sensor for boron neutron capture therapy. (M. Taniguchi, T. Meguro, H.
Tanaka, S.-I. Kuroki)
ARS-8 (R4P2-8): Preliminary survey of nuclide for epithermal neutron measurement using gel detector. (K.
Tanaka, Y. Sakurai, T. Kajimoto, H. Tanaka, T. Takata,
S. Endo)
ARS-9 (R4P2-9): Measurements of neutron fluence and
gamma ray distribution using thermoluminescence
slabs. (K. Shinsho, N. Sugioka, E. Sasaki, H. Tanaka, T.
Takata, W. Chang, S. Matsumoto, G. Wakabayashi, G.
Okada, Y. Koba)
ARS-11 (R4P2-11): Development and evaluation of 3D
gel dosimeter for the measurement of dose distribution
in BNCT. (S. Hayashi, Y. Sakurai, M. Suzuki, T. Takata)
ARS-12 (R4P2-12): Establishment of beam-quality estimation method in BNCT irradiation field using dual
phantom technique (VI). (Y. Sakurai, N. Kondo, T. Takata, H. Tanaka, M. Suzuki)
ARS-13 (R4P2-13): Development of real-time boron-concentration estimation method using gamma-ray
telescope system for BNCT. (Y. Sakurai, D. Fu, T. Takata, H. Tanaka, M. Suzuki)
ARS-14 (R4P2-14): Development of scintillator for
thermal neutron detector in BNCT. (N. Matsubayashi,
H. Tanaka, S. Kurosawa, A. Yamaji, T. Hanada, T.
Takata)
ARS-15 (R4P2-15): Quantitative measurement of 478
keV prompt gamma-rays of boron-neutron capture reaction. (S. Komura, T. Mizumoto, Y. Sakurai, T. Takata,
T. Tanimori, H. Kimura, A. Takada)
ARS-16 (R4P2-16): Visualization of boron dose distribution on a borosilicate glass plate by neutron irradiation. (A. Nohtomi, Y. Kojima, H. Maeda, T. Yamane, G.
Wakabayashi, Y. Sakurai, T. Takata)
ARS-18 (R4P2-18): Investigation of thermal neutron-induced soft errors in semiconductor devices. (H.
Tanaka, R. Nakamura, T. Kato)
ARS-19 (R4P2-19): Dosimetric characteristics of optimized bolus for boron neutron capture therapy. (T. Takata, M. Nojiri, A. Sasaki, Y. Sakurai, H. Tanaka, M.
Suzuki)
ARS-23 (R4P2-23): Three dimensional humanized oral
cancer in vitro model for BNCT. (K. Igawa, K. Izumi, E.
Naito, M. Suzuki, N. Kondo, Y. Sakurai)
ARS-24 (R4P2-24): Boron-10 uptake distribution in 3D
oral cancer model using CR-39 solid state nuclear track
detector. (K. Igawa, R. Ogawara, T. Kusumoto, Y. Sakurai)
ARS-6, ARS-10, ARS-17, ARS-20, ARS-21 and
ARS-22 could not be performed mainly because of the
influence of COVID-19 infection.

R4P2
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PR2-1

Establishment of characterization estimation method in BNCT irradiation field using
Bonner sphere and ionization chamber (VI)

Y. Sakurai, A. Sasaki1, N. Matsubayashi1, M. Nojiri1, D.
Fu1, T. Takata and H. Tanaka
Institute for Integrated Radiation and Nuclear Science,
Kyoto University
1
Graduate School of Engineering, Kyoto University
INTRODUCTION: Development in accelerator-based
irradiation systems for BNCT is underway. In the near
future, BNCT using these newly developed systems may
be carried out at multiple facilities across the world. Considering this situation, it is important that the estimations
for dose quantity and quality are performed consistently
among several irradiation fields, and that the equivalency
of BNCT is guaranteed, within and across BNCT systems.
Then, we are establishing QA/QC system for BNCT.
As part of the QA/QC system, we are developing estimation method for neutron energy spectrum using Bonner
sphere [1]. For our spectrometer using Bonner sphere,
liquid such as pure water and/or boric acid solution is
used as the moderator. A multi-layer concentric-sphere
case with several sphere shells is prepared. The moderator and its diameter are changeable without entering the
irradiation room, by the remote supply and drainage of
liquid moderator in the several layers. For the detector,
activation foils are remotely changed, or online measurement is performed using SOF detector, etc.
In 2022, verification experiments for the prototype Remote-changeable Bonner-sphere Spectrometer (RBS)
were performed using Heavy Water Neutron Irradiation
Facility installed in Kyoto University Reactor
(KUR-HWNIF) as in the previous year [2].
MATERIALS AND METHODS: In the neutron energy spectrometry by Bonner-sphere, the combinations of
the moderator material and diameter should be previously
decided and prepared. Of course, the more information
can be obtained as the more moderators and detectors are
prepared. However, the information number from those
measured data is less than the combination number, because of the overlapped regions among the combinations.
The selection is important, in which the more information
number is obtained for the combination number.
The combination of moderator and detector is decided,
for that the response functions cannot be approximated
by the linear functions of the other response functions.
The accuracy and precision for the spectrometry can be
higher, because the independent information can be obtained from the measurement by the respective combinations. We were developed the selection method, High
Independence Selection (HIS) [3].
On the assumption of the application in the standard
epi-thermal neutron irradiation mode of KUR-HWNIF,
the combination of the moderators for boron-10 concentration and diameter was optimized by HIS. Based on this
optimization, the prototype RBS was revised. Some experiments were performed for the characteristic verifica-

tion of the revised prototype RBS at KUR-HWNIF.
RESULTS: The configuration of the revised RBS was
decided as follows. A five-layer concentric spherical
acrylic shell is used as a container. Each acrylic wall is 1
mm in thickness. The moderator injection part is 9 mm in
thickness for each layer. Pure water and 0.12-wt% boric
acid water for boron-10 were used as liquid moderators.
A LiCaF scintillation detector was used as the detector.
Figure 1 shows the outline of the revised prototype RBS.
Unfolding was performed by GRAVEL using the response function of each Bonner sphere corrected by multiplying the ratio for measured/calculated values. The
nominal spectrum of the epi-thermal neutron irradiation
mode was input as an initial guess.
The comparison between the nominal spectrum and unfolded spectrum was performed. The spectrum obtained
by the unfolding reproduced the nominal spectrum relatively and absolutely well. It was confirmed that the accuracy of the revised prototype RBS was more improved
than the previous version.
CONCLUSION: We have the plans to perform (1) the
further revision of the prototype RBS and (2) the preparation of a Bonner sphere spectrometer including the remote mechanism for the supply and drainage of the liquid
moderators.

Fig. 1. Outline of the revised prototype of RBS.
REFERENCES:
[1] S. Shiraishi et al., Appl. Radiat. Isot., 163 (2020)
109213.
[2] Y. Sakurai and T. Kobayashi, Nucl. Instr. Meth. A,
453 (2000) 569-596.
[3] H. Ueda, Doctoral Thesis, Kyoto Univ., (2016).

R4P2-1
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Study on neutron energy spectrometry for epi-thermal neutrons

S. Yoshihashi, A. Yamazaki, K. Watababe1, Y. Oshima1, A.
Uritani and Y. ...