Search

Radiation cancer therapy with ultra-high dose rate exposure, so called FLASH radiotherapy, appears to reduce normal tissue damage without compromising tumor response. The aim of this study was to clarify whether FLASH exposure of proton beam would be effective in reducing the DNA strand break induction. We applied a simple model system, pBR322 plasmid DNA in aqueous 1× TE solution, where DNA single strand breaks (SSBs) and double strand breaks (DSBs) can be precisely quantified by gel electrophoresis. Plasmid DNA were exposed to 27.5 MeV protons in the conventional dose rate of 0.05 Gy/s (CONV) and ultra-high dose rate of 40 Gy/s (FLASH). With both dose rate, the kinetics of the SSB and DSB induction were proportional to absorbed dose. The SSB induction of FLASH was significantly less than CONV, which were 8.79 ± 0.14 (10-3 SSB per Gy per molecule) and 10.8 ± 0.68 (10-3 SSB per Gy per molecule), respectively. The DSB induction of FLASH was also slightly less than CONV, but difference was not significant. Altogether, 30 MeV proton beam at 40 Gy/s reduced SSB and not DSB, thus its effect may not be significant in reducing lethal DNA damage that become apparent in acute radiation effect.

第37回宇宙環境利用シンポジウム (2023年1月17日-18日. オンライン開催), Space Utilization Research (January 17-18, 2023. Online Meeting), 資料番号: SA6000180015, G-9

We have been studying the effectiveness of direct action, which induces clustered DNA damage leading to cell killing, relative to indirect action. Here a new criterion Direct Ation-Based Biological Effectiveness (DABBLE) is proposed to understand the contribution of direct action for cell killing induced by C ions. DABBLE is defined as the ratio of direct action to indirect action. To derive this ratio, we describe survival curves of mammalian cells as a function of the number of OH radicals produced 1 ps and 100 ns after irradiation, instead of the absorbed dose. By comparing values on the vertical axis of the survival curves at a certain number of OH radicals produced, we successfully discriminate the contribution of direct action induced by C ions from that of indirect action. DABBLE increases monotonically with increasing linear energy transfer (LET) up to 140 keV/μm and then drops, when the survival curves are described by the number of OH radicals 1 ps after irradiation. The trend of DABBLE is in agreement with that of relative biological effectiveness (RBE) of indirect action. In comparison, the value of DABBLE increases monotonically with LET, when the survival curves are described by the number of OH radicals 100 ns after irradiation. This finding implies that the effectiveness of C ion therapy for cancer depends on the contribution of direct action and we can follow the contribution of direct action over time in the chemical phase.

FLASH radiotherapy appears to kill off tumor cells while sparing healthy tissues, by irradiation at ultra high dose rate (>40 Gy s−1). The present study aims to clarify the mechanism of the sparing effect by proton irradiation under the FLASH conditions from a viewpoint of radiation chemistry. To do so, we evaluate radiation chemical yields (G values) of 7-hydroxy-coumarin-3-carboxylic acid (7OH–C3CA), which is produced by water radiolysis using coumarin-3-carboxylic acid (C3CA) solution as a radical scavenger of hydroxyl radicals. We shoot 27.5 MeV protons in the dose rate ranging from 0.05 to 160 Gy s−1. The recombination process of hydroxyl radicals produced is followed by varying the concentration of C3CA from 0.2 to 20 mM, which corresponds to the scavenging time scale from 7.1 to 714 ns. The G value of 7OH–C3CA produced decreases with increasing dose rate on the same scavenging time scale. Additionally, the trend of the relative G value normalized at a scavenging time scale of 100 ns, where radical–radical reaction subsides, is consistent in the examined dose rate range. This finding implies that G values of 7OH–C3CA produced reduce with increasing dose rate due to the oxygen depletion. We experimentally present that the sparing effect for healthy tissues would be seen even with a proton beam under the FLASH conditions due to the depletion of oxygen.

第36回宇宙環境利用シンポジウム (2022年1月18日-19日. オンライン開催), Space Utilization Research (January 18-19, 2022. Online Meeting), 資料番号: SA6000168011, G-10

The radiation environment encountered in space differs in nature from that on Earth, consisting mostly of highly energetic ions from protons up to iron, resulting in radiation levels far exceeding the ones present on Earth for occupational radiation workers. Since the beginning of the space era the radiation exposure during space missions has been monitored with various passive and active radiation instruments. Also on-board the International Space Station (ISS) a number of area monitoring devices provide data related to the spatial and temporal variation of the radiation field in – and outside the ISS. The aim of the DOSIS 3D (2012 - ongoing) experiment is the measurement of the radiation environment within the European Columbus Laboratory of the ISS. These measurements are, on the one hand, performed with passive radiation detectors mounted at eleven locations within Columbus for the determination of the spatial distribution of the radiation field parameters and, on the other hand, with two active radiation detectors (DOSTEL) mounted at a fixed position inside Columbus for the determination of the temporal variation of the radiation field parameters. The talk will give an overview of the current results of the data evaluation performed for the passive and active radiation detectors for DOSIS 3D in the years 2012 to 2020 and further focus on the work in progress for data comparison with other passive and active radiation detector systems measuring on-board the ISS.

We investigated the local concentration of α-particles from 211At-labeled trastuzumab antibodies against HER2 (human epidermal growth factor receptor type2) antigens in liver metastasis tissue of mice. Mice carrying metastatic cancer in their liver were injected with 211At-agent. After 12 hours, the liver was removed and sliced, and two tissue samples of liver tissues without lesions and one containing metastatic lesions were mounted on the CR-39 plastic nuclear track detector. Microscope images of the tissues on CR-39 were acquired. After irradiation for 31 hours, the tissues were removed from CR-39. A microscope image of α-particle tracks on CR-39 was acquired after chemical etching. The positions of each tissue sample and the emitted α-particle tracks were adjusted to the same coordinates. The positional distribution of α-particle tracks emitted from 211At was consistent within the tissue. The α-particle tracks were mainly allocated in the tumor region of the tissue. The absorbed dose in individual cells segmented by 10 µm intervals was obtained by the spectroscopic analysis of the LET (linear energy transfer) spectrum. The concentration efficiency, the track density ratio of α-particle tracks in the necrotized tissue, which was the tumor region, to the normal tissue, was found to be 6.0 ± 0.2. In the tumor region, the high LET α-particles deposited a large enough dose to cause lethal damage to the cancer cells. The total absorbed dose ranged from 1 to 7 Gy with a peak at around 2 Gy, which would correspond to 2-3 times higher biologically equivalent dose because of the high RBE of the α-particles emitted from 211At.

第33回宇宙環境利用シンポジウム (2019年1月24日-25日. 宇宙航空研究開発機構宇宙科学研究所(JAXA)(ISAS)), 相模原市, 神奈川県, Space Utilization Research (January 24-25, 2019. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 著者人数: 18名, 資料番号: SA6000132013, レポート番号: G-12

The geometric locations of ion traversals in mammalian cells constitute important information in the study of heavy ion induced biological effect. Single ion traversal through a cellular nucleus produces complex and massive DNA damage at a nanometer level, leading to cell inactivation, mutations, and transformation. We present a novel approach that uses a fluorescent nuclear track detector (FNTD) for the simultaneous detection of the geometrical images of ion traversals and DNA damage in single cells using confocal microscopy. HT1080 or HT1080-53BP1-GFP cells were cultured on the surface of an FNTD and exposed to 5.1 MeV/n neon ions. The positions of the ion traversals were obtained as fluorescent images of FNDT. Localized DNA damage in cells was identified as fluorescent spots of γ-H2AX or 53BP1-GFP. These track images and images of damaged DNA were obtained in a short time using a confocal laser scanning microscope. The geometrical distribution of DNA damage indicated by fluorescent γ-H2AX spots in fixed cells or fluorescent 53BP1-GFP spots in living cells was found to correlate well with the distribution of the ion traversals. This method will be useful for evaluating the number of ion hits on individual cells, not only for micro-beam but also for random beam experiments.

Chemical modification along ion tracks in Poly (allyl diglycol carbonate), PADC, films has been studied by means of Fourier transform infrared (FT-IR) spectrometry, which has exposed to protons and heavy ions in air. Chemical damage parameters, namely, radial size of the track core, in which the considered chemical groups are lost, damage density, which is the number of losses of considered functional groups per unit length of tracks, and radiation chemical yields, G values, for each group are evaluated as a function of the stopping power. The radiation chemical yields are higher at lower stopping powers for each ion and greater with increasing charge at the same stopping powers. Secondary electrons with higher energy should play a significant role to increase the yields by producing damage at a relatively distant place from the ion trajectories.

In order to understand the latent track formation mechanics in polymeric nuclear track detectors, chemical modification along heavy ion tracks in bisphenol A polycarbonate, PC, and poly(allyldiglycol carbonate), PADC, has been examined using Fourier transform infrared, FT-IR, spectrometry. Track core radius for loss of carbonyl has different dependence on the stopping power between PC and PADC, indicating a quite different response to heavy ions from each others. This implies a possibility of controlling the track registration characteristics by changing the molecule structure between two carbonate ester bonds. In PC, the tracks have three different regions. The central region lost all three functional groups of carbonate ester bonds, phenyl rings and methyl groups, which surrounded by the second region in which the carbonate ester bonds and phenyl rings were damaged. In the outer region, the carbonate ester bonds were lost.

Facilities for heavy ion therapies are steadily increasing in number worldwide. One of the advantages of heavy ions is their high relative biological effect (RBE). In a model used at NIRS (National Institute of Radiological Sciences), linear energy transfer (LET) spectra are required to estimate biological dose (physical dose × RBE). The CR-39 plastic charged-particle detector (CR-39) is suitable for measurement of LET. For the present study, done at the Gunma University Heavy Ion Medical Center (GHMC), we measured LET spectra at 11 depths in spread-out Bragg peak (SOBP) irradiation by a 12C beam of 380 MeV/u. The lower threshold of the CR-39 to measure LET was about 5 keV μm−1 due to poor sensitivity for low LET. Then we calculated biological dose and survival fraction distributions and compared them with treatment planning results at GHMC. We used Monte Carlo simulation (Geant4) to calculate LET spectra. The simulation results were in good agreement with the experimental spectra. Moreover, the biological dose and survival fraction distributions estimated from the CR-39 reproduced the treatment planning. The CR-39 is suitable for estimating biological dose in carbon ion therapy.

The origin of Galactic Cosmic Rays (GCRs) nuclei is still unknown. The precise observation of ultra heavy nuclei (Z is greater than or equal to 30) in GCRs is important to resolve the problems remained in cosmic ray astrophysics. Observation program of these nuclei in GCRs is proposed with the use of high performance Solid-State Track Detector (SSTD) on board long-duration balloon or International Space Station (ISS). The program focuses to measure the isotopic abundance above iron-peak elements and the composition of the rare ultra heavy nuclei up to actinide elements with relativistic energy. The observation of their nuclear composition covers a wide range of scientific themes including studies of nucleosynthesis of cosmic ray sources, chemical evolution of galactic material, the characteristic time associated with cosmic rays, such as heating and acceleration mechanism of cosmic ray particles. In order to achieve the objectives, long-duration balloon and/or ISS capable of carrying very large scientific payloads for long extended period is thought as best suited. The possible approach is based on a large telescope array consisting of modularized SSTD stacks., 資料番号: AA0063706014

We report the activities on the working group 'High Energy Cosmic Ray Observation'. We have been developing the CALET (Calorimetric Electron Telescope) instrument on-board the Japanese Experiment Module/Exposed Facility, JEM/EF, of the ISS (International Space Station). We are successfully developing the instruments, and carried out a balloon flight of the proto-type in 2006. The working group hosted two meetings in Japan and two international meetings in US and China to subscribe for the AO of JEM/EF missions by JAXA., 資料番号: AA0063349048

国際アストロバイオロジーワークショップ2013（第6回日本アストロバイオロジーネットワーク年次研究会）（2013年11月28日-30日. 宇宙航空研究開発機構宇宙科学研究所（JAXA)（ISAS)）, 相模原市, 神奈川県, International Astrobiology Workshop 2013 (November 28-30, 2013. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 著者人数: 16名, 資料番号: SA6000008024, レポート番号: 1040

制度:新 ; 文部省報告番号:甲2485号 ; 学位の種類:博士(理学) ; 授与年月日:2007/7/26 ; 早大学位記番号:新4593

第22回宇宙利用シンポジウム(2006年1月17日-19日, 日本学術会議6階会議室 六本木、東京), The Twenty-second Space Utilization Symposium (January 17-19, 2006: Science Council of Japan, Roppongi, Tokyo, Japan), We report the activities on the working group "High Energy Cosmic Ray Observation". We have been developing the CALET instrument on-board the Japanese Experiment Module/ Exposed Facility, JEM/EF, of the ISS. We have successfully concluded the mission concept study and the fundamental technical development. By organizing the working group to prepare the mission proposal, we have done much progress on establishing the international team for instrument development, making a written proposal of the project and constructing a proto-type detector for balloon experiments., 形態: カラー図版あり, 共催: 日本学術会議, 著者人数: 34人, Physical characteristics: Original contains color illustrations, Meeting sponsors: The Science Council of Japan, The Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (ISAS)(JAXA), 資料番号: AA0064113032