Yokoyama, Sumi*; Hamada, Nobuyuki*; Tsujimura, Norio; Kunugita, Naoki*; Nishida, Kazutaka*; Ezaki, Iwao*; Kato, Masahiro*; Okubo, Hideki*
International Journal of Radiation Biology, 99(4), p.604 - 619, 2023/04
In April 2011, the International Commission on Radiological Protection recommended reducing the occupational equivalent dose limit for the lens. Such a new occupational lens dose limit has thus far been implemented in many countries, and there are extensive discussions toward its regulatory implementation in other countries. In Japan, discussions in the Japan Health Physics Society (JHPS) began in April 2013 and in Radiation Council in July 2017, and the new occupational lens dose limit was implemented into regulation in April 2021. To share our experience, we have published a series of papers summarizing situations in Japan: the first paper based on information available by early 2017, and the second paper by early 2019. This paper (our third paper of this series) aims to review updated information available by mid-2022, such as regarding regulatory implementation of the new occupational lens dose limit, recent discussions by relevant ministries based on the opinion from the council, establishment process of safety and health management systems, the JHPS guidelines on lens dose monitoring and radiation safety, voluntary countermeasures of the licensees, development of lens dose calibration method, and recent studies on exposure of the lens in nuclear workers and biological effect on the lens.
Sato, Tatsuhiko; Matsuya, Yusuke; Hamada, Nobuyuki*
International Journal of Radiation Oncology, Biology, Physics, 114(1), p.153 - 162, 2022/09
The microdosimetric kinetic model, which was originally developed for estimating cell surviving fractions for various radiations, was improved to be capable of estimating the mean and uncertainty of RBE for skin reactions. The parameter used in the model was independently determined from in vitro measurements of dermal cell survival and in vivo measurements of skin reactions taken from 8 and 23 papers, respectively. Our model quantitatively revealed that RBE for skin reactions tend to be higher than that for dermal cell survival. RBE of various mono-energetic radiations calculated from this model confirmed that the past evaluations made by ICRP and NCRP a few decades ago are still supported by recent experimental data. Conclusions: Our model can play important roles not only in medical physics for avoiding unnecessary skin reactions in particle therapy and BNCT but also in radiation protection for future decision making of the recommended RBE values.
Matsuya, Yusuke; Kai, Takeshi; Sato, Tatsuhiko; Ogawa, Tatsuhiko; Hirata, Yuho; Yoshii, Yuji*; Parisi, A.*; Liamsuwan, T.*
International Journal of Radiation Biology, 98(2), p.148 - 157, 2022/02
When investigating radiation-induced biological effects, it is essential to perform detailed track-structure simulations explicitly by considering each atomic interaction in liquid water (which is equivalent to human tissues) at sub-cellular and DNA scales. The Particle and Heavy Ion Transport code System (PHITS) is a Monte Carlo code which can be used for track structure calculations by employing an original electron track-structure mode (etsmode) and the world-famous KURBUC algorithms (PHITS-KURBUC mode) for protons and carbon ions. In this study, the physical features (i.e., range, radial dose and microdosimetry) of these modes have been verified by comparing to the available experimental data and Monte Carlo simulation results reported in literature. In addition, applying the etsmode to radiobiological study, we estimated the yields of single-strand breaks (SSBs), double-strand breaks (DSBs) and complex DSBs, and evaluated the dependencies of DNA damage yields on incident electron energy. As a result, the simulations suggested that DNA damage types are intrinsically related with the spatial patterns of ionization and electronic excitations and that approximately 500 eV electron can cause much complex DSBs. In this paper, we show the development status of the PHITS track-structure modes and its application to radiobiological research, which would be expected to identify the underlying mechanisms of radiation effects based on physics.
Sato, Tatsuhiko; Hashimoto, Shintaro; Inaniwa, Taku*; Takada, Kenta*; Kumada, Hiroaki*
International Journal of Radiation Biology, 97(10), p.1450 - 1460, 2021/10
The stochastic microdosimetric kinetic (SMK) model is one of the most sophisticated and precise models used in the estimation of the relative biological effectiveness of carbon-ion radiotherapy (CRT) and boron neutron capture therapy (BNCT). Through the introduction of Taylor expansion (TE) or fast Fourier transform (FFT), we developed two simplified SMK models and implemented them into the Particle and Heavy Ion Transport code System (PHITS). This study enables the instantaneous calculation of the equieffective dose for CRT and BNCT, considering their cellular-scale dose heterogeneities. Treatment-planning systems that use the improved PHITS as a dose-calculation engine are under development.
Hirato, Misaki*; Onizawa, Misato*; Baba, Yuji*; Haga, Yoshinori; Fujii, Kentaro*; Wada, Shinichi*; Yokoya, Akinari*
International Journal of Radiation Biology, 7 Pages, 2020/00
Yokoyama, Sumi*; Hamada, Nobuyuki*; Tsujimura, Norio
International Journal of Radiation Biology, 95(8), p.1103 - 1112, 2019/08
Watanabe, Ritsuko; Hattori, Yuya; Kai, Takeshi
International Journal of Radiation Biology, 92(11), p.660 - 664, 2016/11
To understand the effect of internal exposure of Cs, we focus on estimation of microscopic energy deposition pattern and DNA damage induced by directly emitted electrons (beta-rays, internal conversion electrons, Auger electrons) from Cs. Monte Carlo track simulation method was used to calculate the microscopic energy deposition pattern. To simulate the energy deposition by directly emitted electrons, we considered the multiple ejections of electrons after internal conversion. Induction process of DNA strand breaks and base lesions was modeled and simulated using Monte Carlo methods for cell mimetic condition. The yield and spatial distribution of simple and complex DNA damage were calculated for the cases of -rays and electrons from Cs. The simulation showed that significant difference of DNA damage spectrum was not caused by the difference between secondary electron spectrum by -rays and directly ejected electron spectrum. The result support that the existing evaluation that internal exposure and external exposure are almost equivalent.
Kai, Takeshi; Yokoya, Akinari; Ukai, Masatoshi; Fujii, Kentaro; Watanabe, Ritsuko
International Journal of Radiation Biology, 92(11), p.654 - 659, 2016/11
Yokota, Yuichiro; Funayama, Tomoo; Muto, Yasuko*; Ikeda, Hiroko; Kobayashi, Yasuhiko
International Journal of Radiation Biology, 91(5), p.383 - 388, 2015/05
We investigated the dependence of the bystander cell-killing effect on radiation dose and quality, and related molecular mechanisms. Human fibroblasts were irradiated with -rays or carbon ions and co-cultured with non-irradiated cells. Survival rates of non-irradiated cells decreased and nitrite concentrations in culture medium increased with increasing doses. Their dose responses were similar between -rays and carbon ions. Treatment of the specific nitric oxide (NO) radical scavenger prevented reductions in survival rates of non-irradiated cells. Negative relationships were observed between survival rates and nitrite concentrations. From these results, it was concluded that the bystander cell-killing effect mediated by NO radicals in human fibroblasts depends on irradiation doses, but not on radiation quality. NO radical production appears to be an important determinant of -ray- and carbon-ion-induced bystander effects.
Autsavapromporn, N.*; Plante, I.*; Liu, C.*; Konishi, Teruaki*; Usami, Noriko*; Funayama, Tomoo; Azzam, E.*; Murakami, Takeshi*; Suzuki, Masao*
International Journal of Radiation Biology, 91(1), p.62 - 70, 2015/01
Radiation-induced bystander effects have important implications in radiotherapy. Their persistence in normal cells may contribute to risk of health hazards, including cancer. This study investigates the role of radiation quality and gap junction intercellular communication (GJIC) in the propagation of harmful effects in progeny of bystander cells. Confluent human skin fibroblasts were exposed to microbeam radiations with different linear energy transfer (LET) by which 0.0360.4% of the cells were directly targeted by radiation. Following 20 population doublings, the cells were harvested and assayed for micronucleus formation, gene mutation and protein oxidation. The results showed that expression of stressful effects in the progeny of bystander cells is dependent on LET.
Kai, Takeshi; Higuchi, Mariko; Fujii, Kentaro; Watanabe, Ritsuko; Yokoya, Akinari
International Journal of Radiation Biology, 88(12), p.928 - 932, 2012/12
Fujii, Kentaro; Fukuda, Yoshihiro; Yokoya, Akinari
International Journal of Radiation Biology, 88(12), p.888 - 894, 2012/12
Oka, Toshitaka; Yokoya, Akinari; Fujii, Kentaro
International Journal of Radiation Biology, 88(12), p.884 - 887, 2012/12
no abstracts in English
Muto, Yasuko; Funayama, Tomoo; Yokota, Yuichiro; Kobayashi, Yasuhiko
International Journal of Radiation Biology, 88(3), p.258 - 266, 2012/03
Sato, Tatsuhiko; Watanabe, Ritsuko; Sihver, L.*; Niita, Koji*
International Journal of Radiation Biology, 88(1-2), p.143 - 150, 2012/01
The microdosimetric function of PHITS has been applied to the biological dose estimation for charged-particle therapy and the risk estimation for astronauts. The former application was performed in combination with the microdosimetric kinetic model, while the latter was done with the radiation quality factor expressed as a function of lineal energy. Owing to the unique features of the microdosimetric function, the improved PHITS has a potential to establish more sophisticated systems for the radiological protection in space as well as the treatment planning of charged-particle therapy.
Yoshihara, Ryohei; Hase, Yoshihiro; Sato, Ryohei*; Takimoto, Koichi*; Narumi, Issei
International Journal of Radiation Biology, 86(2), p.125 - 131, 2010/02
In an effort to assess the characteristics of mutation induced by different LET radiation in higher plants, the mutational effects of carbon-ion beams and -rays were investigated in . The transgenic (Arabidopsis/rpsL) mutation detection system was adopted. Dry seeds of Arabidopsis/rpsL were irradiated with -rays and 208-MeV carbon ions (208-MeV C), and the mutation frequency and mutation spectrum were examined. Our result suggested that 208-MeV C and -rays induced different mutational effects in dry seed.
Yokoya, Akinari; Fujii, Kentaro; Shikazono, Naoya; Akamatsu, Ken; Urushibara, Ayumi; Watanabe, Ritsuko
International Journal of Radiation Biology, 84(12), p.1069 - 1081, 2008/12
The role of Auger effect in inducing DNA damage has been studied using soft X-ray irradiation, which mainly cause photoelectric effect of DNA constituent atoms. As a consequence of Auger decay process, ejected low energy photo- or Auger-electrons might impact on proximately chemical group in the molecule. These highly localized collision events are expected to lead to a clustered DNA damage site within a few nano-meter. We have revealed that soft X-ray (60 keV) induced lesions visualized by the enzymatic probes show much higher yields than those induced by low LET -ray irradiation, and the yields decreased with decreasing soft X-ray energy (below a few keV). These results indicate that the complexity of damage site strongly depends on photo- or Auger electron range. The recent progress that has been made in the study of the process of DNA-radicals as precursors using an EPR apparatus combined with a synchrotron soft X-ray source is also presented.
Fujii, Kentaro; Yokoya, Akinari; Shikazono, Naoya
International Journal of Radiation Biology, 84(12), p.1104 - 1111, 2008/12
To investigate the KLL Auger effect of constituent atoms on DNA damage, dry plasmid DNA (pUC18) films were irradiated with synchrotron monochromatic ultrasoft X-rays. Four photon energies, 270, 380, 435, and 560 eV, respectively, were chosen for the irradiation experiments. Irradiated plasmid DNA was analyzed by agarose gel electrophoresis and the yields of strand breaks were determined by measuring the band intensities of the separated closed circular, open circular and linear forms of the plasmid DNA. The yields of base lesions and clustered damage site including at least one base lesion were determined by the post-irradiation-treatment of the DNA with enzymatic probes (Fpg and Endo III) which convert base lesions into detectable strand breaks.
Akamatsu, Ken; Fujii, Kentaro; Yokoya, Akinari
International Journal of Radiation Biology, 84(12), p.1082 - 1092, 2008/12
The aim of this study is to clarify the difference of DNA damage induced by USX from that by Co-60 -rays. We have recently attended to unaltered base release, strand break terminus and base lesion, focusing on the effect of nitrogen and oxygen K-shell electron ionization. The yields of unaltered bases released were determined by HPLC. To quantify and characterize the strand break termini, the digestion rates of the irradiated DNA pretreated with or without calf intestinal alkaline phosphatase by snake venom phosphodiesterase (SVPD) were measured. This experimental method revealed that the production of the termini, which can not be digested by SVPD, were predominant in comparison with that of SVPD- digestive ones, e.g., with 3'OH, in both USX and -rays. Furthermore, piperidine-treated irradiated DNA was also analyzed by the same method above to quantify piperidine-labile base lesions.
Urushibara, Ayumi*; Shikazono, Naoya; O'Neill, P.*; Fujii, Kentaro; Wada, Seiichi*; Yokoya, Akinari
International Journal of Radiation Biology, 84(1), p.23 - 33, 2008/01
To characterize the complexity of radiation damage to DNA, fully hydrated plasmid DNA was irradiated with He ions. From quantification of the conformational changes of the irradiated samples, the yields of single-(SSB) and double strand break (DSB) were obtained. Base lesions were visualized as additional strand breaks by treatment with base excision repair enzymes. The yield of prompt SSBs does not depend significantly on LET of the He ions, whereas the yield of prompt DSBs increases with increasing LET. The yields of isolated base lesions, revealed by enzymes as additional SSBs, decrease drastically with increasing LET. The sum of the yields of DSB and additional DSBs revealed by the enzymes increase with increasing LET of the He ions except at the highest LET investigated. These results indicate that the yields of clustered damage, revealed as DSB and non-DSB clustered damage sites, increase with increasing ionization density of radiation.