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Furuta, Takuya; Maeyama, Takuya*; Ishikawa, Kenichi*; Fukunishi, Nobuhisa*; Fukasaku, Kazuaki*; Takagi, Shu*; Noda, Shigeho*; Himeno, Ryutaro*; Hayashi, Shinichiro*
Physics in Medicine & Biology, 60(16), p.6531 - 6546, 2015/08
Times Cited Count：10 Percentile：52.03(Engineering, Biomedical)Low reproducibility of dose distribution in inhomogeneous regions such as soft matter near bones is known with the simple dose analysis currently adopted in treatment planning of particle cancer therapy. Therefore a treatment planning system based on Monte Carlo simulation having better accuracy is highly desired. In order to assess the simulation accuracy of a Monte Carlo simulation code in situations closely related to medical application, we performed a comparison of dose distribution in a biological sample obtained by experiment and that by simulation. In particular, we irradiate a carbon beam on a biological sample composed of fresh chicken meat and bones, with a PAGAT gel dosimeter placed behind it, and compare the complex dose distribution in the gel dosimeter created by the beam passing through the inhomogeneous sample. Monte Carlo simulation using PHITS code was conducted by reconstructing the biological sample from its computed tomography images. The simulation accurately reproduced the experimental distal edge structure of the dose distribution with an accuracy under about 2 mm.
Furuta, Takuya; Sato, Tatsuhiko; Ogawa, Tatsuhiko; Niita, Koji*; Ishikawa, Kenichi*; Noda, Shigeho*; Takagi, Shu*; Maeyama, Takuya*; Fukunishi, Nobuhisa*; Fukasaku, Kazuaki*; et al.
Proceedings of Joint International Conference on Mathematics and Computation, Supercomputing in Nuclear Applications and the Monte Carlo Method (M&C + SNA + MC 2015) (CD-ROM), 9 Pages, 2015/04
In Particle and Heavy Ion Transport code System PHITS, two parallel computing functions are prepared to reduce the computational time. One is the distributed-memory parallelization using message passing interface (MPI) and the other is the shared-memory parallelization using OpenMP directives. Each function has advantages and disadvantages, and thus, by adopting both functions in PHITS, it is possible to conduct parallel computing suited for needs of users. It is also possible to conduct the hybrid parallelization by the intra-node OpenMP parallelization and the inter-node MPI parallelization in supercomputer systems. Each parallelization functions were explained together with some application results obtained using a workstation and a supercomputer system, K computer at RIKEN.
Maeyama, Takuya*; Fukunishi, Nobuhisa*; Ishikawa, Kenichi*; Furuta, Takuya; Fukasaku, Kazuaki*; Takagi, Shu*; Noda, Shigeho*; Himeno, Ryutaro*; Fukuda, Shigekazu*
Radiation Physics and Chemistry, 107, p.7 - 11, 2015/02
Times Cited Count：7 Percentile：61.4(Chemistry, Physical)We study the radiological characteristics of VIP polymer gel dosimeters under carbon beam irradiation with energy of 135 and 290 AMeV. To evaluate dose response of VIP polymer gels, the transverse relaxation rate R2 of the dosimeters measured by magnetic resonance imaging (MRI) as a function of linear energy transfer (LET), rather than penetration depth, as is usually done in previous reports. LET is evaluated by use of the particle transport simulation code PHITS. Our results reveal that the dose response decreases with increasing dose-averaged LET and that the response-LET relation also varies with incident carbon beam energy. The latter can be explained by taking into account the contribution from fragmentation products. Furthermore, as an application of the evaluated response-LET relation, we compare the measured and simulated R2 distribution in a VIP gel formed by heterogeneous irradiation and obtain agreement in overall distribution and range within an accuracy of 5% and 1-2 mm, respectively.
Yamashita, Shinichi; Baldacchino, G.*; Maeyama, Takuya*; Taguchi, Mitsumasa; Muroya, Yusa*; Lin, M.*; Kimura, Atsushi; Murakami, Takeshi*; Katsumura, Yosuke
Free Radical Research, 46(7), p.861 - 871, 2012/07
Times Cited Count：16 Percentile：45.02(Biochemistry & Molecular Biology)Radiation-induced reactions in aqueous solutions of a water-soluble coumarin derivative, coumarin-3-carboxyl acid (C3CA), have been investigated by pulse radiolysis with 35-MeV electron beam, final product analysis after 
Co 
-irradiations, and deterministic model simulations. It was found that C3CA reacts with the hydroxyl radical (
OH) as well as the hydrated electron at nearly diffusion-controlled rate constants: 6.8
10
and 2.110
M
s, respectively. Reactivity of C3CA toward O
was not confirmed. Production of a fluorescent molecule 7-hydroxy-coumarin-3-carboxylic acid (7OH-C3CA) was detected by a fluorescence spectrometer coupled with high performance liquid chromatography. Production yields of 7OH-C3CA were in a range from 0.025 to 0.18 (100 eV), depending on irradiation conditions. A variety of the yield with saturating gas, additive, and C3CA concentration implied that there are at least two pathways from scavenging reaction of C3CA toward OH to 7OH-C3CA: peroxidation reaction followed by elimination of perhydroxyl radical and disproportionation reaction. A reaction mechanism involving the two pathways was proposed and incorporated into the simulations, showing good explanation of experimentally measured 7OH-C3CA yields with a constant conversion factor from OH scavenging to 7OH-C3CA production, 4.7%, unless 
-BuOH is not added.
Maeyama, Takuya*; Yamashita, Shinichi; Taguchi, Mitsumasa; Baldacchino, G.*; Sihver, L.*; Murakami, Takeshi*; Katsumura, Yosuke
Radiation Physics and Chemistry, 80(12), p.1352 - 1357, 2011/12
Times Cited Count：11 Percentile：69.32(Chemistry, Physical)Coumari-3-carboxylic acid scavenges OH radical produced in water radiolysis, leading to production of a fluorescence probe at almost constant ratio relative to the amount of the scavenged OH radicals. This was applied in estimation of OH radical yield in water radiolysis especially with therapeutic heavy ions of GeV-class energies, i.e. 
C
beams of 135, 290 and 400 MeV/u. OH yields upstream of the Bragg peaks decreased with increasing penetration depth of the projectile ions while that downstream suddenly jumped up to near the value for low-LET radiations such as 
-rays. This is due to low-LET secondary fragmentation ions produced during long trajectory of the primary projectile C ion. Quantitative explanation by nuclear fragmentation simulations with PHITS code was attempted and resulted in 15-45% underestimation in the region behind the Bragg peaks, which would be due to the difference in geometries between irradiations of the sample solutions and dosimetry with a small ionization chamber.
Maeyama, Takuya*; Yamashita, Shinichi; Baldacchino, G.*; Taguchi, Mitsumasa; Kimura, Atsushi; Murakami, Takeshi*; Katsumura, Yosuke
Radiation Physics and Chemistry, 80(4), p.535 - 539, 2011/04
Times Cited Count：27 Percentile：90.43(Chemistry, Physical)Aqueous coumarin-3-carboxylic Acid (3CCA) solutions were irradiated with eight different ion beams covering LET range from 0.5 to above 2000 eV/nm. 
-values of 7OH-3CCA, one of hydroxylated products in radiolysis of the solutions, have been determined by fluorescence-HPLC technique in 3CCA concentration range from 0.1 to 26 mM. The formation yield of 7OH-3CCA increased with increasing concentration of 3CCA while it decreased with increasing LET value of ion beam. Compared with our previous reports on (OH) at a scavenging capacity of 10
s with absorption spectroscopy, it was found that (7OH-3CCA) is about (4.7
0.6)% of (OH), which is consistent for all of the ion beams used in the present study. However, 7OH-3CCA yields in high CCA concentration region, especially by using extremely high LET ions, were much higher than expected values based on the above conversion factor and (OH) value predicted in theoretical work.
Baldacchino, G.*; Maeyama, Takuya*; Yamashita, Shinichi; Taguchi, Mitsumasa; Kimura, Atsushi; Katsumura, Yosuke; Murakami, Takeshi*
Chemical Physics Letters, 468(4-6), p.275 - 279, 2009/01
Times Cited Count：34 Percentile：78.11(Chemistry, Physical)This paper reports a sensitive method using HPLC-fluorescence detection of OH in liquid water under high-energy heavy-ion irradiation. The coumarin-3-carboxylic-acid (3CCA) molecule was selected for probing OH and providing the fluorescent 7-hydroxy-coumarin-3-carboxylic-acid (7OH-3CCA). Since the concentration limit achievable is better than 1 nM, the radiolytic yields were determined with a sensitivity of 2
10
mol/J for 4.8-GeV-C of and 20-GeV-
Ar
in the ns time-range. They decrease with the linear energy transfer from 2.810
to 1.310 mol/J (C of 11 eV/nm) and 1.510 to 0.910 mol/J (Ar of 90 eV/nm) which is in agreement with the literature data.
Yamashita, Shinichi; Katsumura, Yosuke; Lin, M.; Muroya, Yusa*; Maeyama, Takuya*; Murakami, Takeshi*
Radiation Physics and Chemistry, 77(10-12), p.1224 - 1229, 2008/10
Times Cited Count：16 Percentile：72.52(Chemistry, Physical)Measurements of primary 
-values (at 
10 s after the initial ionizing event) of e
, 
OH and HO were extended to the very high linear energy transfer (LET) region ( 700 eV per nm) near the Bragg peak. Heavy ions (
He
, C, 
Ne
, 
Si
, Ar and 
Fe
) of energies up to 28 GeV were provided by the Heavy Ion Medical Accelerator in Chiba (HIMAC) of the National Institute of Radiological Sciences (NIRS) in Chiba, Japan. Energies of the ions were decreased down to about 10 MeV per u for He using an energy absorber made of polymethylmethacrylate (PMMA) plates in order to vary the LET values. Beam was visualized after passing through the energy absorber using agarose gel of aqueous solution containing methyl viologen and sodium formate in order to determine how long ions can penetrate into water. Based on the information of the penetration depth of ions in samples, much attention was paid to dose correction and LET evaluation. The obtained data were plotted as a function of (
/
)
also instead of LET in order to discuss effects of physical track structures on product yields, resulted in better universality.
Maeyama, Takuya*; Katsumura, Yosuke; Yamashita, Shinichi*; Lin, M.; Muroya, Yusa*; Miyazaki, Toyoaki*; Murakami, Takeshi*; Baldacchino, G.*
no journal, ,
no abstracts in English
Yamashita, Shinichi; Katsumura, Yosuke; Lin, M.; Maeyama, Takuya*; Muroya, Yusa*; Murakami, Takeshi*
no journal, ,
no abstracts in English
OH yields with fluorescent probe, 1; Investigation into reaction mechanism and reactivity toward water decomposition radicals of coumarin-3-carboxylic acidMaeyama, Takuya*; Yamashita, Shinichi; Baldacchino, G.*; Muroya, Yusa*; Taguchi, Mitsumasa; Kimura, Atsushi; Katsumura, Yosuke
no journal, ,
no abstracts in English
Maeyama, Takuya*; Yamashita, Shinichi; Baldacchino, G.*; Taguchi, Mitsumasa; Kimura, Atsushi; Katsumura, Yosuke; Murakami, Takeshi*
no journal, ,
no abstracts in English
Yamashita, Shinichi; Katsumura, Yosuke; Lin, M.; Muroya, Yusa*; Maeyama, Takuya*; Murakami, Takeshi*
no journal, ,
Water radiolysis with highly energetic heavy ions from helium to iron ions (up to 500 MeV per nucleon, corresponding to beta = 0.758) provided from HIMAC (Heavy Ion Medical Accelerator in Chiba) at NIRS (National Institute of Radiological Sciences) has been investigated through yield measurements and simulations of intra-track reactions. Primary yields, which are defined as yields at sub microsecond after irradiation, were measured for wide range of LET (2.2-700 eV/nm). Dynamics of heavy ion tracks were also discussed based on yield measurement, in which various scavenger concentrations were used. In parallel to the measurements, simulations based on Monte-Carlo method and diffusion kinetic model were conducted.
Maeyama, Takuya*; Yamashita, Shinichi; Baldacchino, G.*; Katsumura, Yosuke; Taguchi, Mitsumasa; Kimura, Atsushi; Muroya, Yusa*; Murakami, Takeshi*
no journal, ,
Detailed mechanism in which effectiveness of heavy ions in cancer therapy are derived from is not known well. It is inevitably important to examine water radiolysis with high-energy heavy ions because water is main component of human body. Among several water decomposition products, OH is known to be most responsible for radiation induced cell death in indirect actions. OH yield has been reported for heavy-ion irradiations in several works employing absorption analyses. With increasing LET, OH yield decreases monotonically (at least up to several hundred eV per nm). Then, more sensitive way to determine OH yield is preferable for higher LET region. In this work, a fluorescent probe, coumarin-3-carboxylic acid, was applied for OH-yield determination as a sensitive way of quantification of OH radical production. Especially, OH yield near the Bragg peaks was discussed.
Maeyama, Takuya*; Yamashita, Shinichi; Baldacchino, G.*; Katsumura, Yosuke; Muroya, Yusa*; Taguchi, Mitsumasa; Kimura, Atsushi; Murakami, Takeshi*
no journal, ,
Fluorescent probe 7-Hydroxy-coumarin-3-carboxylic acid, which is a product of reaction between Coumarin-3-carboxylic acid (CCA) and hydroxyl radical (OH), was applied to estimation of the yield of OH produced in water radiolysis with heavy ions of energies up to 28 GeV provided from HIMAC (Heavy Ion Medical Accelerator in Chiba). LET was varied from 0.2 for -ray or fast electron beam to 346 eV/nm for iron ion beam. With changing the concentration of CCA in the range from 0.1 to 26 mM, scavenging time scale was varied from 4 ns to 1 
s, at which time scale intra-track reactions between water decomposition radicals including OH are significant.
Yamashita, Shinichi; Katsumura, Yosuke; Maeyama, Takuya*; Lin, M.; Muroya, Yusa*; Murakami, Takeshi*; Meesungnoen, J.*; Jay-Gerin, J.-P.*
no journal, ,
Water radiolysis with heavy ions, from helium to iron ions, of very high energies up to 28 GeV (namely several hundred MeV per nucleon) has been studied in this work. Simulations based on diffusion kinetic model were performed to examine correlation between initial track structures at the beginning of the chemical stage, 10-12 s, and primary yields as well as to estimate the validity of classical track structure model for highly energetic heavy ions.
Yamashita, Shinichi; Katsumura, Yosuke; Maeyama, Takuya*; Murakami, Takeshi*; Meesungnoen, J.*; Jay-Gerin, J.-P.*
no journal, ,
Primary yields in water radiolysis with relativistic heavy ions from Heavy Ion Medical Accelerator in Chiba (HIMAC) of National Institute of Radiological Sciences (NIRS) have been measured covering wide range of beam conditions. Experimental results were summarized and compared with results obtained not only in a deterministic simulation but also in a stochastic one. Heavy-ion track structure was discussed from microscopic viewpoints based on the experimental and simulation results.
OH yield near the Bragg peakMaeyama, Takuya*; Yamashita, Shinichi; Katsumura, Yosuke; Baldacchino, G.*; Taguchi, Mitsumasa; Kimura, Atsushi; Murakami, Takeshi*
no journal, ,
Aqueous solution of Coumarin-3-carboxylic acid (CCA) has been applied to yield measurement of OH in water. Production yield of a fluorescent probe, 7OH-CCA, which is a stable product produced after scavenging reaction for OH by CCA, was determined by using HPLC connected to a fluorometer. Taking sensitiveness of fluorometry as an advantage, OH yields near the Bragg peaks, which are known very small compared to those in plateau LET region, have been measured. Contribution of fragmentations, which are known to be significant near the Bragg peaks of high-energy heavy ions, is also being discussed.
Maeyama, Takuya*; Yamashita, Shinichi*; Baldacchino, G.*; Katsumura, Yosuke*; Taguchi, Mitsumasa; Kimura, Atsushi; Muroya, Yusa*; Murakami, Takeshi*
no journal, ,
no abstracts in English
Yamashita, Shinichi; Katsumura, Yosuke; Maeyama, Takuya*; Lin, M.; Muroya, Yusa*; Murakami, Takeshi*; Jay-Gerin, J.-P.*; Meesungnoen, J.*
no journal, ,
Although water is a main component of human cells and its interaction with ionizing radiations are of crucial importance, understanding of water radiolysis with heavy ions of energies comparable to those used in actual cancer treatments is not sufficient. Recently, such highly energetic heavy ions are available at the Heavy Ion Medical Accelerator in Chiba (HIMAC) of the National Institute of Radiological Sciences (NIRS), Chiba, Japan. We have carried out measurements of primary yields of main water decomposition products, hydrated electron (e), hydroxyl radical (OH) and hydrogen peroxide (HO) with heavy ions from He to Fe of energies up to 28 GeV (corresponding LET varies from 2 to 700 keV/m) provided from the HIMAC. Note that primary yields are defined as the yields at 100 ns after irradiation, which can be regarded as a time scale when diffusions and intra-track reactions of initial products are almost terminated. Then, such yields are important because they inherently involve information of initial track structure and dynamics of water decomposition products during track expansion. In the present study, not only such measurements but also discussions based on the measured data were conducted by simulations.
