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Endesfelder D, Kulka U, Bucher M, Giesen U, Garty G, Beinke C, Port M, Gruel G, Gregoire E, Terzoudi G, Triantopoulou S, Ainsbury EA, Moquet J, Sun M, Prieto MJ, Moreno Domene M, Barquinero JF, Pujol-Canadell M, Vral A, Baeyens A, Wojcik A, Oestreicher U. International Comparison Exercise for Biological Dosimetry after Exposures with Neutrons Performed at Two Irradiation Facilities as Part of the BALANCE Project. Cytogenet Genome Res 2023; 163:163-177. [PMID: 37071978 PMCID: PMC10641373 DOI: 10.1159/000530728] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2022] [Accepted: 04/10/2023] [Indexed: 04/20/2023] Open
Abstract
In the case of a radiological or nuclear event, biological dosimetry can be an important tool to support clinical decision-making. During a nuclear event, individuals might be exposed to a mixed field of neutrons and photons. The composition of the field and the neutron energy spectrum influence the degree of damage to the chromosomes. During the transatlantic BALANCE project, an exposure similar to a Hiroshima-like device at a distance of 1.5 km from the epicenter was simulated, and biological dosimetry based on dicentric chromosomes was performed to evaluate the participants ability to discover unknown doses and to test the influence of differences in neutron spectra. In a first step, calibration curves were established by irradiating blood samples with 5 doses in the range of 0-4 Gy at two different facilities in Germany (Physikalisch-Technische Bundesanstalt [PTB]) and the USA (the Columbia IND Neutron Facility [CINF]). The samples were sent to eight participating laboratories from the RENEB network and dicentric chromosomes were scored by each participant. Next, blood samples were irradiated with 4 blind doses in each of the two facilities and sent to the participants to provide dose estimates based on the established calibration curves. Manual and semiautomatic scoring of dicentric chromosomes were evaluated for their applicability to neutron exposures. Moreover, the biological effectiveness of the neutrons from the two irradiation facilities was compared. The calibration curves from samples irradiated at CINF showed a 1.4 times higher biological effectiveness compared to samples irradiated at PTB. For manual scoring of dicentric chromosomes, the doses of the test samples were mostly successfully resolved based on the calibration curves established during the project. For semiautomatic scoring, the dose estimation for the test samples was less successful. Doses >2 Gy in the calibration curves revealed nonlinear associations between dose and dispersion index of the dicentric counts, especially for manual scoring. The differences in the biological effectiveness between the irradiation facilities suggested that the neutron energy spectrum can have a strong impact on the dicentric counts.
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Affiliation(s)
- David Endesfelder
- Department of Effects and Risks of Ionising and Non-Ionising Radiation, Federal Office for Radiation Protection (BfS), Oberschleißheim, Germany,
| | - Ulrike Kulka
- Department of Effects and Risks of Ionising and Non-Ionising Radiation, Federal Office for Radiation Protection (BfS), Oberschleißheim, Germany
| | - Martin Bucher
- Department of Effects and Risks of Ionising and Non-Ionising Radiation, Federal Office for Radiation Protection (BfS), Oberschleißheim, Germany
| | - Ulrich Giesen
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
| | - Guy Garty
- Radiological Research Accelerator Facility (RARAF), Columbia University, Irvington, New York, USA
| | | | - Matthias Port
- Bundeswehr Institute of Radiobiology, Munich, Germany
| | - Gaetan Gruel
- Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PSE-Santé, SERAMED, LRAcc, Fontenay-aux-Roses, France
| | - Eric Gregoire
- Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PSE-Santé, SERAMED, LRAcc, Fontenay-aux-Roses, France
| | - Georgia Terzoudi
- Health Physics, Radiobiology & Cytogenetics Laboratory, National Centre for Scientific Research "Demokritos,", Athens, Greece
| | - Sotiria Triantopoulou
- Health Physics, Radiobiology & Cytogenetics Laboratory, National Centre for Scientific Research "Demokritos,", Athens, Greece
| | - Elizabeth A Ainsbury
- Radiation, Chemicals and Environmental Hazards Directorate, UK Health Security Agency, Chilton, Oxfordshire, UK
| | - Jayne Moquet
- Radiation, Chemicals and Environmental Hazards Directorate, UK Health Security Agency, Chilton, Oxfordshire, UK
| | - Mingzhu Sun
- Radiation, Chemicals and Environmental Hazards Directorate, UK Health Security Agency, Chilton, Oxfordshire, UK
| | - María Jesús Prieto
- Centro de Oncología Radioterápica, Laboratorio de Dosimetría Biológica, Hospital General Universitario Gregorio Marañón, Madrid, Spain
| | - Mercedes Moreno Domene
- Centro de Oncología Radioterápica, Laboratorio de Dosimetría Biológica, Hospital General Universitario Gregorio Marañón, Madrid, Spain
| | - Joan-Francesc Barquinero
- Departament de Biologia Animal, Unitat d'Antropologia Biològica, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - Monica Pujol-Canadell
- Departament de Biologia Animal, Unitat d'Antropologia Biològica, Universitat Autònoma de Barcelona, Bellaterra, Spain
| | - Anne Vral
- Faculty of Medicine and Health Sciences, Department of Human Structure and Repair, Radiobiology Research Unit, Ghent University, Gent, Belgium
| | - Ans Baeyens
- Faculty of Medicine and Health Sciences, Department of Human Structure and Repair, Radiobiology Research Unit, Ghent University, Gent, Belgium
| | - Andrzej Wojcik
- Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
- Institute of Biology, Jan Kochanowski University, Kielce, Poland
| | - Ursula Oestreicher
- Department of Effects and Risks of Ionising and Non-Ionising Radiation, Federal Office for Radiation Protection (BfS), Oberschleißheim, Germany
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Royba E, Repin M, Balajee AS, Shuryak I, Pampou S, Karan C, Wang YF, Lemus OD, Obaid R, Deoli N, Wuu CS, Brenner DJ, Garty G. Validation of a High-Throughput Dicentric Chromosome Assay Using Complex Radiation Exposures. Radiat Res 2023; 199:1-16. [PMID: 35994701 PMCID: PMC9947868 DOI: 10.1667/rade-22-00007.1] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Accepted: 10/24/2022] [Indexed: 01/12/2023]
Abstract
Validation of biodosimetry assays is routinely performed using primarily orthovoltage irradiators at a conventional dose rate of approximately 1 Gy/min. However, incidental/ accidental exposures caused by nuclear weapons can be more complex. The aim of this work was to simulate the DNA damage effects mimicking those caused by the detonation of a several kilotons improvised nuclear device (IND). For this, we modeled complex exposures to: 1. a mixed (photons + IND-neutrons) field and 2. different dose rates that may come from the blast, nuclear fallout, or ground deposition of radionuclides (ground shine). Additionally, we assessed whether myeloid cytokines affect the precision of radiation dose estimation by modulating the frequency of dicentric chromosomes. To mimic different exposure scenarios, several irradiation systems were used. In a mixed field study, human blood samples were exposed to a photon field enriched with neutrons (ranging from 10% to 37%) from a source that mimics Hiroshima's A-bomb's energy spectrum (0.2-9 MeV). Using statistical analysis, we assessed whether photons and neutrons act in an additive or synergistic way to form dicentrics. For the dose rates study, human blood was exposed to photons or electrons at dose rates ranging from low (where the dose was spread over 32 h) to extremely high (where the dose was delivered in a fraction of a microsecond). Potential effects of cytokine treatment on biodosimetry dose predictions were analyzed in irradiated blood subjected to Neupogen or Neulasta for 24 or 48 h at the concentration recommended to forestall manifestation of an acute radiation syndrome in bomb survivors. All measurements were performed using a robotic station, the Rapid Automated Biodosimetry Tool II, programmed to culture lymphocytes and score dicentrics in multiwell plates (the RABiT-II DCA). In agreement with classical concepts of radiation biology, the RABiT-II DCA calibration curves suggested that the frequency of dicentrics depends on the type of radiation and is modulated by changes in the dose rate. The resulting dose-response curves suggested an intermediate dicentric yields and additive effects of photons and IND-neutrons in the mixed field. At ultra-high dose rate (600 Gy/s), affected lymphocytes exhibited significantly fewer dicentrics (P < 0.004, t test). In contrast, we did not find the dose-response modification effects of radiomitigators on the yields of dicentrics (Bonferroni corrected P > 0.006, ANOVA test). This result suggests no bias in the dose predictions should be expected after emergency cytokine treatment initiated up to 48 h prior to blood collection for dicentric analysis.
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Affiliation(s)
- Ekaterina Royba
- Center for Radiological Research, Columbia University Irving Medical Center, New York, New York
| | - Mikhail Repin
- Center for Radiological Research, Columbia University Irving Medical Center, New York, New York
| | - Adayabalam S. Balajee
- Radiation Emergency Assistance Center/Training Site (REAC/TS), Cytogenetic Biodosimetry Laboratory (CBL), Oak Ridge Institute for Science and Education, Oak Ridge Associated Universities, Oak Ridge, Tennessee
| | - Igor Shuryak
- Center for Radiological Research, Columbia University Irving Medical Center, New York, New York
| | - Sergey Pampou
- Columbia Genome Center High-Throughput Screening facility, Columbia University Irving Medical Center, New York, New York
| | - Charles Karan
- Columbia Genome Center High-Throughput Screening facility, Columbia University Irving Medical Center, New York, New York
| | - Yi-Fang Wang
- Department of Radiation Oncology, Columbia University Irving Medical Center, New York, New York
| | - Olga Dona Lemus
- Department of Radiation Oncology, Columbia University Irving Medical Center, New York, New York
| | - Razib Obaid
- Radiological Research Accelerator facility, Columbia University Irving Medical Center, Irvington, New York
- Currently at Stanford Linear Accelerator Center National Accelerator Laboratory, Menlo Park, California
| | - Naresh Deoli
- Radiological Research Accelerator facility, Columbia University Irving Medical Center, Irvington, New York
| | - Cheng-Shie Wuu
- Department of Radiation Oncology, Columbia University Irving Medical Center, New York, New York
| | - David J. Brenner
- Center for Radiological Research, Columbia University Irving Medical Center, New York, New York
| | - Guy Garty
- Center for Radiological Research, Columbia University Irving Medical Center, New York, New York
- Radiological Research Accelerator facility, Columbia University Irving Medical Center, Irvington, New York
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High-Accuracy Relative Biological Effectiveness Values Following Low-Dose Thermal Neutron Exposures Support Bimodal Quality Factor Response with Neutron Energy. Int J Mol Sci 2022; 23:ijms23020878. [PMID: 35055062 PMCID: PMC8779315 DOI: 10.3390/ijms23020878] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 12/24/2021] [Accepted: 12/30/2021] [Indexed: 12/04/2022] Open
Abstract
Theoretical evaluations indicate the radiation weighting factor for thermal neutrons differs from the current International Commission on Radiological Protection (ICRP) recommended value of 2.5, which has radiation protection implications for high-energy radiotherapy, inside spacecraft, on the lunar or Martian surface, and in nuclear reactor workplaces. We examined the relative biological effectiveness (RBE) of DNA damage generated by thermal neutrons compared to gamma radiation. Whole blood was irradiated by 64 meV thermal neutrons from the National Research Universal reactor. DNA damage and erroneous DNA double-strand break repair was evaluated by dicentric chromosome assay (DCA) and cytokinesis-block micronucleus (CBMN) assay with low doses ranging 6–85 mGy. Linear dose responses were observed. Significant DNA aberration clustering was found indicative of high ionizing density radiation. When the dose contribution of both the 14N(n,p)14C and 1H(n,γ)2H capture reactions were considered, the DCA and the CBMN assays generated similar maximum RBE values of 11.3 ± 1.6 and 9.0 ± 1.1, respectively. Consequently, thermal neutron RBE is approximately four times higher than the current ICRP radiation weighting factor value of 2.5. This lends support to bimodal peaks in the quality factor for RBE neutron energy response, underlining the importance of radiological protection against thermal neutron exposures.
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Hafner L, Walsh L, Schneider U. Cancer incidence risks above and below 1 Gy for radiation protection in space. LIFE SCIENCES IN SPACE RESEARCH 2021; 28:41-56. [PMID: 33612179 DOI: 10.1016/j.lssr.2020.09.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 08/31/2020] [Accepted: 09/04/2020] [Indexed: 05/22/2023]
Abstract
The risk assessment quantities called lifetime attributable risk (LAR) and risk of exposure-induced cancer (REIC) are used to calculate the cumulative cancer incidence risks for astronauts, attributable to radiation exposure accumulated during long term lunar and Mars missions. These risk quantities are based on the most recently published epidemiological data on the Life Span Study (LSS) of Japanese A-bomb survivors, who were exposed to γ-rays and neutrons. In order to analyze the impact of a different neutron RBE on the risk quantities, a model for the neutron relative biological effectiveness (RBE) relative to gammas in the LSS is developed based on an older dataset with less follow-up time. Since both risk quantities are based on uncertain quantities, such as survival curves, and REIC includes deterministic radiation induced non-cancer mortality risks, modelled with data based on the general population, the risks for astronauts may not be optimally estimated. The suitability of these risk assessment measures for the use of cancer risk calculation for astronauts is discussed. The work presented here shows that the use of a higher neutron RBE than the value of 10, traditionally used in the LSS risk models, can reduce the risks up to almost 50%. Additionally, including an excess absolute risk (EAR) baseline scaling also increases the risks by between 0.4% and 8.1% for the space missions considered in this study. Using just an EAR model instead of an equally weighted EAR and excess relative risk (ERR) model can decrease the cumulative risks for the considered missions by between 0.4% and 4.1% if no EAR baseline scaling is applied. If EAR baseline scaling is included, the calculated risks with the EAR- and the mixed model, as well as the risks calculated with just the ERR model are almost identical and only small differences in the uncertainties are visible.
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Affiliation(s)
- Luana Hafner
- Department of Physics, ETH Zurich, Otto-Stern-Weg 1, 8093 Zurich, Switzerland.
| | - Linda Walsh
- Department of Physics, Science Faculty, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.
| | - Uwe Schneider
- Department of Physics, Science Faculty, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland; Radiotherapy Hirslanden, Witellikerstrasse 40, 8032 Zurich, Switzerland.
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Walsh L, Schneider U, Fogtman A, Kausch C, McKenna-Lawlor S, Narici L, Ngo-Anh J, Reitz G, Sabatier L, Santin G, Sihver L, Straube U, Weber U, Durante M. Research plans in Europe for radiation health hazard assessment in exploratory space missions. LIFE SCIENCES IN SPACE RESEARCH 2019; 21:73-82. [PMID: 31101157 DOI: 10.1016/j.lssr.2019.04.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2019] [Revised: 04/09/2019] [Accepted: 04/11/2019] [Indexed: 05/04/2023]
Abstract
The European Space Agency (ESA) is currently expanding its efforts in identifying requirements and promoting research towards optimizing radiation protection of astronauts. Space agencies use common limits for tissue (deterministic) effects on the International Space Station. However, the agencies have in place different career radiation exposure limits (for stochastic effects) for astronauts in low-Earth orbit missions. Moreover, no specific limits for interplanetary missions are issued. Harmonization of risk models and dose limits for exploratory-class missions are now operational priorities, in view of the short-term plans for international exploratory-class human missions. The purpose of this paper is to report on the activity of the ESA Topical Team on space radiation research, whose task was to identify the most pertinent research requirements for improved space radiation protection and to develop a European space radiation risk model, to contribute to the efforts to reach international consensus on dose limits for deep space. The Topical Team recommended ESA to promote the development of a space radiation risk model based on European-specific expertise in: transport codes, radiobiological modelling, risk assessment, and uncertainty analysis. The model should provide cancer and non-cancer radiation risks for crews implementing exploratory missions. ESA should then support the International Commission on Radiological Protection to harmonize international models and dose limits in deep space, and guarantee continuous support in Europe for accelerator-based research configured to improve the models and develop risk mitigation strategies.
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Affiliation(s)
- L Walsh
- Department of Physics, Science Faculty, University of Zürich, Zurich, Switzerland
| | - U Schneider
- Department of Physics, Science Faculty, University of Zürich, Zurich, Switzerland
| | | | - C Kausch
- GSI Helmholtzzentrum für Schwerionenforschung, Biophysics Department, Darmstadt, Germany
| | | | - L Narici
- Department of Physics, University Tor Vergata, and INFN, Roma-2 Section, Rome, Italy
| | - J Ngo-Anh
- ESA-ESTEC, Nordwijk, the Netherlands
| | - G Reitz
- Nuclear Physics Institute, Czech Academy of Sciences, Prague, Czechia; Radiation Biology, Institue for Aerospace Medicine, DLR, Cologne, Germany
| | - L Sabatier
- Fundamental Research Division, D3P, CEA, Paris-Saclay, France
| | - G Santin
- ESA-ESTEC, Nordwijk, the Netherlands
| | - L Sihver
- Atominstitut, Technische Universität Wien, Wien, Austria; MedAustron, Wiener Neustadt, Austria
| | | | - U Weber
- GSI Helmholtzzentrum für Schwerionenforschung, Biophysics Department, Darmstadt, Germany
| | - M Durante
- GSI Helmholtzzentrum für Schwerionenforschung, Biophysics Department, Darmstadt, Germany; Technische Universität Darmstadt, Darmstadt, Germany.
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Hirai Y, Cordova KA, Kodama Y, Hamasaki K, Awa AA, Tomonaga M, Mine M, Cullings HM, Nakamura N. Tooth enamel ESR doses and cytogenetic doses of Nagasaki atomic-bomb survivors in comparison with DS02R1 doses. Int J Radiat Biol 2018; 95:321-328. [PMID: 30496019 DOI: 10.1080/09553002.2019.1552807] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
PURPOSE Cancer risks for Nagasaki survivors once appeared to be lower than for Hiroshima survivors. The possibility that this was due to overestimation of the doses for the Nagasaki survivors was tested by measuring biological doses of Nagasaki survivors and comparing them with DS02R1 individual doses as previously done for Hiroshima survivors. MATERIALS AND METHODS The electron spin resonance (ESR) method and cytogenetic method were used to estimate radiation doses for 24 Nagasaki survivors, and the results were compared to calculated DS02R1 doses. RESULTS Six factory workers and 10 other survivors showed ESR or cytogenetically estimated doses that were in reasonably good agreement with their DS02R1 doses, while one factory worker was found to have an ESR dose estimate of nearly one half of the DS02R1 dose to the eye lens (a proxy organ for teeth). A few outliers were also observed. CONCLUSIONS Although apparently lower cancer risks were observed in the past for Nagasaki survivors when compared to Hiroshima survivors, the present results do not indicate the existence of a trend that DS02R1 doses are overestimated when compared with biologically estimated tooth or cytogenetic doses. This observation is in line with the recent disappearance of the city difference in cancer risks.
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Affiliation(s)
- Yuko Hirai
- a Department of Molecular Biosciences , Radiation Effects Research Foundation , Minami ku , Hiroshima , Japan
| | - Kismet A Cordova
- b Department of Statistics , Radiation Effects Research Foundation , Minami ku , Hiroshima , Japan
| | - Yoshiaki Kodama
- a Department of Molecular Biosciences , Radiation Effects Research Foundation , Minami ku , Hiroshima , Japan
| | - Kanya Hamasaki
- a Department of Molecular Biosciences , Radiation Effects Research Foundation , Minami ku , Hiroshima , Japan
| | - Akio A Awa
- a Department of Molecular Biosciences , Radiation Effects Research Foundation , Minami ku , Hiroshima , Japan
| | - Masao Tomonaga
- c Department of Hematology , Atomic Bomb Disease Institute, Nagasaki University , Nagasaki , Japan.,d Megumino-oka Nagasaki Genbaku Home Clinics , Nagasaki , Japan
| | - Mariko Mine
- e Research Center for Nuclear Weapons Abolition, Nagasaki University , Nagasaki , Japan.,f Nagasaki Atomic Bomb Casualty Council , Nagasaki , Japan
| | - Harry M Cullings
- b Department of Statistics , Radiation Effects Research Foundation , Minami ku , Hiroshima , Japan
| | - Nori Nakamura
- a Department of Molecular Biosciences , Radiation Effects Research Foundation , Minami ku , Hiroshima , Japan
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Sasaki MS, Endo S, Hoshi M, Nomura T. Neutron relative biological effectiveness in Hiroshima and Nagasaki atomic bomb survivors: a critical review. JOURNAL OF RADIATION RESEARCH 2016; 57:583-595. [PMID: 27614201 PMCID: PMC5137296 DOI: 10.1093/jrr/rrw079] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Revised: 05/09/2016] [Accepted: 06/12/2016] [Indexed: 06/06/2023]
Abstract
The calculated risk of cancer in humans due to radiation exposure is based primarily on long-term follow-up studies, e.g. the life-span study (LSS) on atomic bomb (A-bomb) survivors in Hiroshima and Nagasaki. Since A-bomb radiation consists of a mixture of γ-rays and neutrons, it is essential that the relative biological effectiveness (RBE) of neutrons is adequately evaluated if a study is to serve as a reference for cancer risk. However, the relatively small neutron component hampered the direct estimation of RBE in LSS data. To circumvent this problem, several strategies have been attempted, including dose-independent constant RBE, dose-dependent variable RBE, and dependence on the degrees of dominance of intermingled γ-rays. By surveying the available literature, we tested the chromosomal RBE of neutrons as the biological endpoint for its equivalence to the microdosimetric quantities obtained using a tissue-equivalent proportional counter (TEPC) in various neutron fields. The radiation weighting factor, or quality factor, Qn, of neutrons as expressed in terms of the energy dependence of the maximum RBE, RBEm, was consistent with that predicted by the TEPC data, indicating that the chromosomally measured RBE was independent of the magnitude of coexisting γ-rays. The obtained neutron RBE, which varied with neutron dose, was confirmed to be the most adequate RBE system in terms of agreement with the cancer incidence in A-bomb survivors, using chromosome aberrations as surrogate markers. With this RBE system, the cancer risk in A-bomb survivors as expressed in unit dose of reference radiation is equally compatible with Hiroshima and Nagasaki cities, and may be potentially applicable in other cases of human radiation exposure.
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Affiliation(s)
- Masao S Sasaki
- Kyoto University and National Institute of Biomedical Innovation, Health and Nutrition, 17-12 Shironosato, Nagaokakyo-shi, Kyoto 617-0835, Japan
| | - Satoru Endo
- Quantum Energy Application, Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-hiroshima, Hiroshima 739-8527, Japan
| | - Masaharu Hoshi
- Institute for Peace Science, Hiroshima University, 1-1-89 Higashisenda, Naka-ku, Hiroshima 730-0053, Japan
| | - Taisei Nomura
- National Institute of Biomedical Innovation, Health and Nutrition, 7-6-8 Saito-Asagi, Ibaraki-shi, Osaka 567-0086, Japan
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Schneider U, Hälg R. The Impact of Neutrons in Clinical Proton Therapy. Front Oncol 2015; 5:235. [PMID: 26557501 PMCID: PMC4617104 DOI: 10.3389/fonc.2015.00235] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Accepted: 10/06/2015] [Indexed: 11/13/2022] Open
Abstract
In proton therapy, high-energy proton beams cause the production of secondary neutrons. This leads to an unwanted dose contribution, which can be considerable for tissues outside of the target volume regarding the long-term health of cancer patients. Due to the high biological effectiveness of neutrons with regard to cancer induction, small neutron doses can be important. Published comparisons of neutron dose measurements and the corresponding estimates of cancer risk between different treatment modalities differ over orders of magnitude. In this report, the controversy about the impact of the neutron dose in proton therapy is critically discussed and viewed in the light of new epidemiological studies. In summary, the impact of neutron dose on cancer risk can be determined correctly only if the dose distributions are carefully measured or computed. It is important to include not only the neutron component into comparisons but also the complete deposition of energy as precisely as possible. Cancer risk comparisons between different radiation qualities, treatment machines, and techniques have to be performed under similar conditions. It seems that in the past, the uncertainty in the models which lead from dose to risk were overestimated when compared with erroneous dose comparisons. Current risk models used with carefully obtained dose distributions predict a second cancer risk reduction for active protons vs. photons and a more or less constant risk of passive protons vs. photons. Those findings are in general agreement with newly obtained epidemiologically results.
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Affiliation(s)
- Uwe Schneider
- Institute of Physics, Science Faculty, University of Zürich, Zürich, Switzerland
- Radiotherapy Hirslanden, Zürich, Switzerland
| | - Roger Hälg
- Institute of Physics, Science Faculty, University of Zürich, Zürich, Switzerland
- Radiotherapy Hirslanden, Zürich, Switzerland
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Tawn EJ, Curwen GB, Jonas P, Gillies M, Hodgson L, Cadwell KK. Chromosome Aberrations Determined by FISH in Radiation Workers from the Sellafield Nuclear Facility. Radiat Res 2015; 184:296-303. [PMID: 26305405 DOI: 10.1667/rr14125.1] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Workers from the Sellafield nuclear facility (Cumbria, UK) with occupational exposures to external sources of ionizing radiation were examined for translocation frequencies in peripheral blood lymphocytes using fluorescence in situ hybridization (FISH). This is an extension of an earlier study of retired workers, and includes analyses of additional samples from the earlier collection, bringing the total to 321. Another 164 samples from both current and retired employees, including 26 repeat samples, were obtained from a new collection, thus giving a combined dataset of 459 workers. This all-male population of workers was divided into 6 dose groups comprising 97 with recorded external occupational doses <50 mGy, 118 with 50-249 mGy, 129 with 250-499 mGy, 89 with 500-749 mGy, 17 with 750-999 mGy and 9 with >1,000 mGy. Univariate analysis showed a significant association between external dose and translocation frequency (P < 0.001) with the estimate of slope ± standard error being 1.174 ± 0.164 × 10(-2) translocations per Gy. Multivariate analysis revealed that age increased the rate of translocations by 0.0229 ± 0.0052 × 10(-2) per year (P < 0.001). However, the impact of age adjustment on the radiation dose response for translocation frequencies was minor with the new estimate of slope ± standard error being 1.163 ± 0.162 × 10(-2) translocations per Gy. With the dose response for the induction of translocations by chronic in vivo low-LET radiation now well characterized, cytogenetic analysis can play an integral role in retrospective dose reconstruction of chronic exposure in epidemiological studies of exposed populations.
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Affiliation(s)
- E Janet Tawn
- a Centre for Integrated Genomic Medical Research (CIGMR), Centre for Epidemiology, Institute of Population Health, The University of Manchester, Manchester, M13 9PT, United Kingdom.,b Formerly of Westlakes Research Institute2, Westlakes Science and Technology Park, Moor Row, Cumbria, CA24 3LN, United Kingdom
| | - Gillian B Curwen
- a Centre for Integrated Genomic Medical Research (CIGMR), Centre for Epidemiology, Institute of Population Health, The University of Manchester, Manchester, M13 9PT, United Kingdom.,b Formerly of Westlakes Research Institute2, Westlakes Science and Technology Park, Moor Row, Cumbria, CA24 3LN, United Kingdom
| | - Patricia Jonas
- c Formerly of Northern Genetics Service, Institute of Genetic Medicine, International Centre for Life, Newcastle University, Newcastle upon Tyne, NE1 3BZ, United Kingdom
| | - Michael Gillies
- b Formerly of Westlakes Research Institute2, Westlakes Science and Technology Park, Moor Row, Cumbria, CA24 3LN, United Kingdom.,d Public Health England, Centre for Radiation, Chemical and Environmental Hazards, Westlakes Science and Technology Park, Moor Row, Cumbria, CA24 3HU, United Kingdom
| | - Leanne Hodgson
- b Formerly of Westlakes Research Institute2, Westlakes Science and Technology Park, Moor Row, Cumbria, CA24 3LN, United Kingdom
| | - Kevin K Cadwell
- b Formerly of Westlakes Research Institute2, Westlakes Science and Technology Park, Moor Row, Cumbria, CA24 3LN, United Kingdom
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Schmid TE, Canella L, Kudejova P, Wagner FM, Röhrmoser A, Schmid E. The effectiveness of the high-LET radiations from the boron neutron capture [10B(n,α) 7Li] reaction determined for induction of chromosome aberrations and apoptosis in lymphocytes of human blood samples. RADIATION AND ENVIRONMENTAL BIOPHYSICS 2015; 54:91-102. [PMID: 25428113 DOI: 10.1007/s00411-014-0577-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Accepted: 11/18/2014] [Indexed: 06/04/2023]
Abstract
Provided that a selective accumulation of (10)B-containing compounds is introduced in tumor cells, following irradiation by thermal neutrons produces high-LET alpha-particles ((4)He) and recoiling lithium-7 ((7)Li) nuclei emitted during the capture of thermalized neutrons (0.025 eV) from (10)B. To estimate the biological effectiveness of this boron neutron capture [(10)B(n,α)(7)Li] reaction, the chromosome aberration assay and the flow cytometry apoptosis assay were applied. At the presence of the clinically used compounds BSH (sodium borocaptate) and BPA (p-boronophenylalanine), human lymphocytes were irradiated by sub-thermal neutrons. For analyzing chromosome aberrations, human lymphocytes were exposed to thermally equivalent neutron fluences of 1.82 × 10(11) cm(-2) or 7.30 × 10(11) cm(-2) (corresponding to thermal neutron doses of 0.062 and 0.248 Gy, respectively) in the presence of 0, 10, 20, and 30 ppm of BSH or BPA. Since the kerma coefficient of blood increased by 0.864 × 10(-12) Gy cm(2) per 10 ppm of (10)B, the kerma coefficients in blood increase from 0.34 × 10(-12) cm(2) (blood without BSH or BPA) up to 2.93 × 10(-12) Gy cm(2) in the presence of 30 ppm of (10)B. For the (10)B(n, α)(7)Li reaction, linear dose-response relations for dicentrics with coefficients α = 0.0546 ± 0.0081 Gy(-1) for BSH and α = 0.0654 ± 0.0075 Gy(-1) for BPA were obtained at 0.062 Gy as well as α = 0.0985 ± 0.0284 Gy(-1) for BSH and α = 0.1293 ± 0.0419 Gy(-1) for BPA at 0.248 Gy. At both doses, the corresponding (10)B(n, α)(7)Li reactions from BSH and BPA are not significantly different. A linear dose-response relation for dicentrics also was obtained for the induction of apoptosis by the (10)B(n, α)(7)Li reaction at 0.248 Gy. The linear coefficients α = 0.0249 ± 0.0119 Gy(-1) for BSH and α = 0.0334 ± 0.0064 Gy(-1) for BPA are not significantly different. Independently of the applied thermal neutron doses of 0.062 Gy or 0.248 Gy, the (10)B(n, α)(7)Li reaction from 30 ppm BSH or BPA induced an apparent RBE of about 2.2 for the production of dicentrics as compared to exposure to thermal neutrons alone. Since the apparent RBE value is defined as the product of the RBE of a thermal neutron dose alone times a boron localization factor which depends on the concentration of a (10)B-containing compound, this localization factor determines the biological effectiveness of the (10)B(n, α)(7)Li reaction.
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Affiliation(s)
- T E Schmid
- Klinikum rechts der Isar, Klinik für Strahlentherapie und Radiologische Onkologie, Technische Universität München, Ismaningerstr. 22, 81675, Munich, Germany.
| | - L Canella
- Forschungsneutronenquelle Heinz-Maier-Leibnitz (FRM II), Technische Universität München, 85747, Garching, Germany
| | - P Kudejova
- Forschungsneutronenquelle Heinz-Maier-Leibnitz (FRM II), Technische Universität München, 85747, Garching, Germany
| | - F M Wagner
- Forschungsneutronenquelle Heinz-Maier-Leibnitz (FRM II), Technische Universität München, 85747, Garching, Germany
| | - A Röhrmoser
- Forschungsneutronenquelle Heinz-Maier-Leibnitz (FRM II), Technische Universität München, 85747, Garching, Germany
| | - E Schmid
- Department for Anatomy and Cell Biology, University of Munich, 80336, Munich, Germany
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Abstract
Several radiation-related professional societies have concluded that carcinogenic risks associated with doses below 50-100 mSv are either too small to be detected, or are nonexistent. This is especially important in the context of doses from medical imaging. Radiation exposure to the public from medical imaging procedures is rising around the world, primarily due to increased utilization of computed tomography. Professional societies and advisory bodies consistently recommend against multiplying small doses by large populations to predict excess radiation-induced cancers, in large part because of the potential for sensational claims of health impacts which do not adequately take the associated uncertainties into account. Nonetheless, numerous articles have predicted thousands of future cancers as a result of CT scanning, and this has generated considerable concern among patients and parents. In addition, some authors claim that we now have direct epidemiological evidence of carcinogenic risks from medical imaging. This paper critically examines such claims, and concludes that the evidence cited does not provide direct evidence of low-dose carcinogenicity. These claims themselves have adverse public health impacts by frightening the public away from medically justified exams. It is time for the medical and scientific communities to be more assertive in responding to sensational claims of health risks.
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Affiliation(s)
- Brant A. Ulsh
- Principal Health Physicist, M.H. Chew & Associates, Livermore, CA
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12
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Cullings HM, Pierce DA, Kellerer AM. Accounting for Neutron Exposure in the Japanese Atomic Bomb Survivors. Radiat Res 2014; 182:587-98. [DOI: 10.1667/rr13663.1] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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13
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Schmid E, Wagner FM, Canella L, Romm H, Schmid TE. RBE of thermal neutrons for induction of chromosome aberrations in human lymphocytes. RADIATION AND ENVIRONMENTAL BIOPHYSICS 2013; 52:113-121. [PMID: 23263356 DOI: 10.1007/s00411-012-0449-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Accepted: 12/10/2012] [Indexed: 06/01/2023]
Abstract
The induction of chromosome aberrations in human lymphocytes irradiated in vitro with slow neutrons was examined to assess the maximum low-dose RBE (RBE(M)) relative to (60)Co γ-rays. For the blood irradiations, cold neutron beam available at the prompt gamma activation analysis facility at the Munich research reactor FRM II was used. The given flux of cold neutrons can be converted into a thermally equivalent one. Since blood was taken from the same donor whose blood had been used for previous irradiation experiments using widely varying neutron energies, the greatest possible accuracy was available for such an estimation of the RBE(M) avoiding the inter-individual variations or differences in methodology usually associated with inter-laboratory comparisons. The magnitude of the coefficient α of the linear dose-response relationship (α = 0.400 ± 0.018 Gy(-1)) and the derived RBE(M) of 36.4 ± 13.3 obtained for the production of dicentrics by thermal neutrons confirm our earlier observations of a strong decrease in α and RBE(M) with decreasing neutron energy lower than 0.385 MeV (RBE(M) = 94.4 ± 38.9). The magnitude of the presently estimated RBE(M) of thermal neutrons is-with some restrictions-not significantly different to previously reported RBE(M) values of two laboratories.
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Affiliation(s)
- E Schmid
- Department for Anatomy and Cell Biology, Ludwig-Maximilians-University of Munich, 80336 Munich, Germany.
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Beyreuther E, Dörr W, Lehnert A, Lessmann E, Pawelke J. Relative biological effectiveness of 25 and 10 kV X-rays for the induction of chromosomal aberrations in two human mammary epithelial cell lines. RADIATION AND ENVIRONMENTAL BIOPHYSICS 2009; 48:333-340. [PMID: 19290536 DOI: 10.1007/s00411-009-0221-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2008] [Accepted: 02/25/2009] [Indexed: 05/27/2023]
Abstract
Administration of ionizing radiation for diagnostic purposes can be associated with a risk for the induction of tumors. Therefore, particularly with regard to general screening programs, e.g. with mammography, cost-benefit considerations must be discussed including risk estimation depending upon the radiation quality administered. The present study was initiated to investigate the in vitro X-ray energy dependence for the induction of chromosomal aberrations in the two mammary epithelial cell lines, 184A1 and MCF-12A. The induced excess fragments, dicentric chromosomes and centric rings were analyzed and the relative biological effectiveness (RBE) was determined for 10 and 25 kV X-rays relative to 200 kV X-rays. The assumed energy dependence with higher values for 10 kV X-rays was confirmed for the excess fragments, with RBE(M) values of 1.92 +/- 0.26 and 1.40 +/- 0.12 for 10 kV X-rays and 1.17 +/- 0.12 and 0.97 +/- 0.10 for 25 kV photons determined for cell lines 184A1 and MCF-12A, respectively. Meaningful results for the induction of dicentric chromosomes and centric rings were obtained only for higher doses with RBE values of 1.31 +/- 0.21 and 1.70 +/- 0.29 for 184A1 and 1.08 +/- 0.08 and 1.43 +/- 0.12 for MCF-12A irradiated with 25 and 10 kV X-rays, respectively.
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Affiliation(s)
- Elke Beyreuther
- Institute of Radiation Physics, Forschungszentrum Dresden-Rossendorf, Dresden, Germany.
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Sasaki MS. Advances in the biophysical and molecular bases of radiation cytogenetics. Int J Radiat Biol 2009; 85:26-47. [PMID: 19205983 DOI: 10.1080/09553000802641185] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
PURPOSE For more than 70 years radiation cytogenetics has continued to be a topic of major concern in relation to the action of radiation on living cells. To date, diverse cytogenetic findings have developed into orderly, quantitative interpretations and have stimulated numerous biophysical models. However, it is generally agreed that any one of the models used alone is still unable to explain all aspects of the observed chromosomal effects. In this review, a large number of radiation-induced chromosome aberration findings from the literature are reassessed with special attention given to the reaction kinetics and the relevant molecular processes. CONCLUSION It is now clear that DNA double-strand breaks (DSB) are an integral component of radiation-induced chromosome aberration. At the nexus of the maintenance of genome integrity, cells are equipped with excellent systems to repair DSB, notably non-homologous end-joining (NHEJ) and homologous recombination repair (HRR). These repair mechanisms are strictly regulated along with the DNA turnover cycle. NHEJ functions in all phases of the cell cycle, whereas HRR has a supplementary role specifically in S/G2 phase, where homologous DNA sequences are available in close proximity. The repair pathways are further regulated by a complex nuclear dynamism, where DSB are sensed and large numbers of repair proteins are recruited and assembled to form a repair complex involving multiple DSB. Considering such DSB repair dynamism, radiation-induced chromosome aberrations could be well understood as DSB-DSB pairwise interactions associated with the NHEJ pathway in all phases of the cell cycle and misrepair of a single DSB associated with the complementary HRR pathway in late S/G2 phase.
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Affiliation(s)
- M S Sasaki
- Radiation Biology Center, Kyoto University, Yoshida-konoecho, Sakyo-ku, Kyoto, Japan.
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Schmid E, Wagner FM, Romm H, Walsh L, Roos H. Dose-response relationship of dicentric chromosomes in human lymphocytes obtained for the fission neutron therapy facility MEDAPP at the research reactor FRM II. RADIATION AND ENVIRONMENTAL BIOPHYSICS 2009; 48:67-75. [PMID: 18979115 DOI: 10.1007/s00411-008-0202-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2008] [Accepted: 10/12/2008] [Indexed: 05/27/2023]
Abstract
The biological effectiveness of neutrons from the neutron therapy facility MEDAPP (mean neutron energy 1.9 MeV) at the new research reactor FRM II at Garching, Germany, has been analyzed, at different depths in a polyethylene phantom. Whole blood samples were exposed to the MEDAPP beam in special irradiation chambers to total doses of 0.14-3.52 Gy at 2-cm depth, and 0.18-3.04 Gy at 6-cm depth of the phantom. The neutron and gamma-ray absorbed dose rates were measured to be 0.55 Gy min(-1) and 0.27 Gy min(-1) at 2-cm depth, while they were 0.28 and 0.25 Gy min(-1) at 6-cm depth. Although the irradiation conditions at the MEDAPP beam and the RENT beam of the former FRM I research reactor were not identical, neutrons from both facilities gave a similar linear-quadratic dose-response relationship for dicentric chromosomes at a depth of 2 cm. Different dose-response curves for dicentrics were obtained for the MEDAPP beam at 2 and 6 cm depth, suggesting a significantly lower biological effectiveness of the radiation with increasing depth. No obvious differences in the dose-response curves for dicentric chromosomes estimated under interactive or additive prediction between neutrons or gamma-rays and the experimentally obtained dose-response curves could be determined. Relative to (60)Co gamma-rays, the values for the relative biological effectiveness at the MEDAPP beam decrease from 5.9 at 0.14 Gy to 1.6 at 3.52 Gy at 2-cm depth, and from 4.1 at 0.18 Gy to 1.5 at 3.04 Gy at 6-cm depth. Using the best possible conditions of consistency, i.e., using blood samples from the same donor and the same measurement techniques for about two decades, avoiding the inter-individual variations in sensitivity or the differences in methodology usually associated with inter-laboratory comparisons, a linear-quadratic dose-response relationship for the mixed neutron and gamma-ray MEDAPP field as well as for its fission neutron part was obtained. Therefore, the debate on whether the fission-neutron induced yield of dicentric chromosomes increases linearly with dose remains open.
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Affiliation(s)
- E Schmid
- Radiobiological Institute, University of Munich, Schillerstrasse 42, 80336, Munich, Germany.
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17
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Sasaki MS, Nomura T, Ejima Y, Utsumi H, Endo S, Saito I, Itoh T, Hoshi M. Experimental Derivation of Relative Biological Effectiveness of A-Bomb Neutrons in Hiroshima and Nagasaki and Implications for Risk Assessment. Radiat Res 2008; 170:101-17. [DOI: 10.1667/rr1249.1] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2007] [Accepted: 04/07/2008] [Indexed: 11/03/2022]
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Schneider U, Walsh L. Cancer risk estimates from the combined Japanese A-bomb and Hodgkin cohorts for doses relevant to radiotherapy. RADIATION AND ENVIRONMENTAL BIOPHYSICS 2008; 47:253-63. [PMID: 18157543 DOI: 10.1007/s00411-007-0151-y] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2006] [Accepted: 12/06/2007] [Indexed: 05/20/2023]
Abstract
Most information on the dose-response of radiation-induced cancer is derived from data on the A-bomb survivors who were exposed to gamma-rays and neutrons. Since, for radiation protection purposes, the dose span of main interest is between 0 and 1 Gy, the analysis of the A-bomb survivors is usually focused on this range. However, estimates of cancer risk for doses above 1 Gy are becoming more important for radiotherapy patients and for long-term manned missions in space research. Therefore in this work, emphasis is placed on doses relevant for radiotherapy with respect to radiation-induced solid cancer. The analysis of the A-bomb survivor's data was extended by including two extra high-dose categories (4-6 Sv and 6-13 Sv) and by an attempted combination with cancer data on patients receiving radiotherapy for Hodgkin's disease. In addition, since there are some recent indications for a high neutron dose contribution, the data were fitted separately for three different values for the relative biological effectiveness (RBE) of the neutrons (10, 35 and 100) and a variable RBE as a function of dose. The data were fitted using a linear, a linear-exponential and a plateau-dose-response relationship. Best agreement was found for the plateau model with a dose-varying RBE. It can be concluded that for doses above 1 Gy there is a tendency for a nonlinear dose-response curve. In addition, there is evidence of a neutron RBE greater than 10 for the A-bomb survivor data. Many problems and uncertainties are involved in combing these two datasets. However, since very little is currently known about the shape of dose-response relationships for radiation-induced cancer in the radiotherapy dose range, this approach could be regarded as a first attempt to acquire more information on this area. The work presented here also provides the first direct evidence that the bending over of the solid cancer excess risk dose response curve for the A-bomb survivors, generally observed above 2 Gy, is due to cell killing effects.
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Affiliation(s)
- Uwe Schneider
- Division of Medical Physics, Department of Radiation Oncology and Nuclear Medicine, The Triemli Hospital Zürich, 8063 Zürich, Switzerland.
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Watanabe H, Kashimoto N, Kajimura J, Ishikawa M, Kamiya K. Tumor induction by monoenergetic neutrons in B6C3F1 mice. JOURNAL OF RADIATION RESEARCH 2007; 48:205-10. [PMID: 17443058 DOI: 10.1269/jrr.0614] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
This study was undertaken to investigate induction of tumors by monoenergetic neutrons in B6C3F1 mice. Individual groups of 6 week-old animals of both sexes (about 30 mice/group) were exposed to 0.5 Gy of various monoenergetic neutrons (dose rate 0.5 cGy/min) and then observed for 13 months. The incidences of tumors (mainly liver neoplasms) in non-irradiated male and female controls were 11% and 0%, respectively. In the irradiated animals, the incidences were 53%, 50%, 60% and 43% in males, and 75%, 81%, 71%, and 85% in females, after 0.18, 0.32, 0.6 and 1.0 MeV neutron exposure, respectively. There were no significant differences in the tumor induction rate among the different energy groups.
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Affiliation(s)
- Hiromitsu Watanabe
- Department of Experimental Oncology, Research Institute for Radiation Biology and Medicine, Hiroshima University.
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