記述言語：日本語   出版者・発行元：Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment  

Although optical imaging of muon beams is a possible method for range determination, it has been limited to two-dimensional (2D) projection images. For the precise measurement of an optical image of a muon beam, three-dimensional (3D) imaging is desired. To measure a 3D optical image, we conducted optical imaging of muon beams using a plastic scintillator plate set in a water phantom. When this plate was immersed in the water phantom, irradiation with a positive muon beam was carried out from along the plate's sides. Optical images of the scintillator plate were acquired using a charge-coupled device (CCD) camera from the side during irradiation with a positive muon beam. The imaging system was moved in 10-mm steps perpendicular to the beam direction to acquire a set of sliced optical images of the beam. These sliced images were stacked and interpolated to form a 3D optical image, and the depth and lateral profiles were evaluated. From the depth profiles derived from the 3D optical image, the Bragg peak position was estimated. The lateral profiles at the Bragg peak could also be derived. We confirmed that 3D imaging of muon beams is feasible and in fact a promising method for measuring sliced optical images at any position, which is a capability that is useful for research on muon beams as well as for future muon radiotherapy.

DOI： 10.1016/j.nima.2021.165768

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記述言語：日本語   出版者・発行元：Journal of Instrumentation  

Although optical imaging of decayed positrons and muons can provide promising methods, it has been attempted only for muons without a collimator, and the beam characteristics with collimators, such as peak position or beam spread in depth and lateral directions, have not yet been evaluated. Therefore, we conducted optical imaging of decayed positrons and muons with different collimators. For the imaging of decayed positrons, Cherenkov-light imaging in fluorescein (FS) water was used, while imaging of a plastic scintillator block was used for the imaging of muons. We conducted these imaging trials during irradiation with 84.5-MeV/c positive muons to an FS water phantom or a plastic scintillator block using a cooled charge-coupled device (CCD) camera with each collimator of a different diameter attached to the beam port. We could measure the Cherenkov-light images of FS water of decayed positrons and optical images of muons using the plastic scintillator block for all collimators. The depth profiles of the Cherenkov-light images were slightly wider for the muons with the collimators of larger diameters, although the estimated peak depths were nearly the same for all collimators. The lateral profiles of the Cherenkov light were wider for the muons when using collimators of larger diameters. Asymmetry in the directions of positron emissions from the muons was observed for all collimators. The depth profiles of the optical image of muons using a plastic scintillator block had nearly the same shape. The estimated lateral widths of the optical images of the plastic scintillator block were the same sizes as the collimator diameters within a 1.1-mm difference at a 10-mm depth of the scintillator block, and the widths were wider at the Bragg peak. With these measured optical images, we conclude that Cherenkov-light imaging of decayed positrons in water and optical imaging of muons using a plastic scintillator block with collimators are useful methods for determining not only peak position but also beam width as well as the asymmetry of the directions of positron emissions from the muons.

DOI： 10.1088/1748-0221/16/08/P08062

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記述言語：日本語   出版者・発行元：Physical Review D  

We developed a CANDLES-III system to study the neutrinoless double beta (0νββ) decay of Ca48. The proposed system employs 96 CaF2 scintillation crystals (305 kg) with natural Ca (Canat) isotope which corresponds 350 g of Ca48. External backgrounds were rejected using a 4π active shield of a liquid scintillator surrounding the CaF2 crystals. The internal backgrounds caused by the radioactive impurities within the CaF2 crystals can be reduced effectively through analysis of the signal pulse shape. We analyzed the data obtained in the Kamioka underground for a live-time of 130.4 days to evaluate the feasibility of the low background measurement with the CANDLES-III detector. Using Monte Carlo simulations, we estimated the background rate from the radioactive impurities in the CaF2 crystals and the rate of high energy γ-rays caused by the (n,γ) reactions induced by environmental neutrons. The expected background rate was in a good agreement with the measured rate, i.e., approximately 10-3 events/keV/yr/(kg of Canat), in the 0νββ window. In conclusion, the background candidates were estimated properly by comparing the measured energy spectrum with the background simulations. With this measurement method, we performed the first search for 0νββ decay in a low background condition using a detector on the scale of hundreds of kg of nonenriched Ca. Deploying scintillators enriched in Ca48 will increase the sensitivity strongly. Ca48 has a high potential for use in 0νββ decay search, and is expected to be useful for the development of a next-generation detector for highly sensitive measurements.

DOI： 10.1103/PhysRevD.103.092008

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記述言語：日本語   出版者・発行元：Journal of Instrumentation  

Determining the absorbed dose distributions in phantoms for X-ray beams of high-energy medical linear accelerators (LINAC) is an important task in the quality control of a system. Although optical imaging of water during irradiation of X-ray beams from a LINAC is a promising method, depth dose profiles show underestimation in the deeper parts of the water, mainly due to the angular dependency of Cerenkov-light produced in water. To solve this problem, the authors change camera angles from 0 degree to 10 degrees and obtain optical images with a high-sensitivity cooled charge coupled device (CCD) camera during X-ray beam irradiation. Furthermore, the authors calculate the Cerenkov-light distributions with different camera angles using Monte Carlo simulation and the obtained depth profiles. Then, these depth profiles are evaluated and compared with those of a planning system. In both measured and simulated distributions, the light intensity increases as the angle increases. The measured depth profile of 10 degrees was nearly identical to the planning system. The percentage differences of depth profile between the measured optical image at the angle of 10 degrees and the planning system was -1.7 % at 100 mm depth, and the average difference was 0.8 %. We conclude that optical imaging with that angle is a promising method for reducing the error due to the angular dependency of Cerenkov-light.

DOI： 10.1088/1748-0221/16/03/T03001

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記述言語：日本語   出版者・発行元：Sensors (Switzerland)  

The two-parameter-fitting method (PFM) is commonly used to calculate the stoppingpower ratio (SPR). This study proposes a new formalism: a three-PFM, which can be used in multiple spectral computed tomography (CT). Using a photon-counting CT system, seven rod-shaped samples of aluminium, graphite, and poly(methyl methacrylate) (PMMA), and four types of biological phantom materials were placed in a water-filled sample holder. The X-ray tube voltage and current were set at 150 kV and 40 μA, respectively, and four CT images were obtained at four threshold settings. A semi-empirical correction method that corrects the difference between the CT values from the photon-counting CT images and theoretical values in each spectral region was also introduced. Both the two-and three-PFMs were used to calculate the effective atomic number and electron density from multiple CT numbers. The mean excitation energy was calculated via parameterisation with the effective atomic number, and the SPR was then calculated from the calculated electron density and mean excitation energy. Then, the SPRs from both methods were compared with the theoretical values. To estimate the noise level of the CT numbers obtained from the photoncounting CT, CT numbers, including noise, were simulated to evaluate the robustness of the aforementioned PFMs. For the aluminium and graphite, the maximum relative errors for the SPRs calculated using the two-PFM and three-PFM were 17.1% and 7.1%, respectively. For the PMMA and biological phantom materials, the maximum relative errors for the SPRs calculated using the twoPFM and three-PFM were 5.5% and 2.0%, respectively. It was concluded that the three-PFM, compared with the two-PFM, can yield SPRs that are closer to the theoretical values and is less affected by noise.

DOI： 10.3390/s21041215

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記述言語：日本語   出版者・発行元：Physica Scripta  

Range, momentum and deviation of momentum determinations of muons are important for quality assessment (QA) of beams. Imaging of annihilation radiations emitted from positrons decayed from positive muons and that of bremsstrahlung x-rays emitted from positrons and secondary electrons from positive muons are possible methods of imaging muons. However, the energies and intensities as well as position distributions of these radiations have not been obvious. Thus we calculated the energy spectrum and the distributions of annihilation radiations as well as bremsstrahlung x-rays produced in water during irradiation of positive muons using Monte Carlo simulation. The calculations were conducted for 84.5 MeV /c positive muons, which is the same beam condition used in an experimental facility at the Japan Proton Accelerator Research Complex (J-PARC). We were able to calculate the energy spectrum as well as the position distributions of annihilation radiations and bremsstrahlung x-rays. The energy spectrum showed a broad distribution of bremsstrahlung x-rays, mainly from decayed positrons with an energy range up to 50 MeV with higher intensity in low-energy bremsstrahlung x-rays. The spectrum also showed a sharp peak at 511-keV from annihilation radiations. The position distribution of annihilation radiations was wider than those of the bremsstrahlung x-rays. The position distribution of the bremsstrahlung x-rays were nearly identical to the Cerenkov-light position distribution emitted by the decayed positrons in water. We conclude that imaging of bremsstrahlung x-rays from decayed positrons by using an x-ray camera is a promising method for the QA of positive muons and that higher spatial resolution images of positron distributions will be measured than those measured by annihilation radiations.

DOI： 10.1088/1402-4896/abcf65

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Medical Physics  

Purpose: The luminescence image of water during the irradiation of carbon ions showed higher intensity at shallow depths than dose distribution due to the contamination of Cerenkov light from secondary electrons. Since Cerenkov light is coherent and polarized for the light produced during the irradiation of carbon ions to water, the reduction of Cerenkov light may be possible with a polarizer. In addition, there is no information on the polarization of the luminescence of water. To clarify these points, we measured the optical images of water during the irradiation of carbon ions with a polarizer by changing the directions of the transmission axis. Methods: Imaging was conducted using a cooled charge-coupled device (CCD) camera during the irradiation of 241.5 MeV/n energy carbon ions to a water phantom with a polarizer in front of the lens by changing the transmission axis parallel and perpendicular to the carbon-ion beam. Results: With the polarizer parallel to the carbon-ion beam, the intensity at the shallow depth was ~26% higher than that measured with the polarizer perpendicular to the beam. We found no significant intensity difference between these two images at deeper depths where the Cerenkov light was not included. The difference image of the parallel and perpendicular directions showed almost the same image as the simulated Cerenkov light distribution. Using the measured difference image, correction of the Cerenkov component was possible from the measured luminescence image of water during the irradiation of carbon ions. Conclusion: We could measure the difference of the Cerenkov light component by changing the transmission axis of the polarizer. Also we clarified that there was no difference in the luminescence of water by changing the transmission axis of the polarizer.

DOI： 10.1002/mp.14600

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記述言語：日本語   出版者・発行元：Scientific Reports  

Optical imaging of particle beams is a promising method for range and width estimations. However it was not clear that optical imaging was possible for muons. To clarify this, we conducted optical imaging of muons, since high-intensity muons are now available at J-PARC. We irradiated positive muons with different momenta to water or plastic scintillator block, and imaged using a charge-coupled device (CCD) camera during irradiation. The water and plastic scintillator block produced quite different images. The images of water during irradiation of muons produced elliptical shape light distribution at the end of the ranges due to Cherenkov-light from the positrons produced by positive muon decay, while, for the plastic scintillator block, we measured images similar to the dose distributions. We were able to estimate the ranges of muons as well as the measurement of the asymmetry of the direction of the positron emission by the muon decays from the optical images of the water, although the measured ranges were 4 mm to 5 mm larger than the calculated values. The ranges and widths of the beams could also be estimated from the optical images of the plastic scintillator block. We confirmed that optical imaging of muons was possible and is a promising method for the quality assessment, research of muons, and the future muon radiotherapy.

DOI： 10.1038/s41598-020-76652-8

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記述言語：日本語  

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記述言語：日本語   出版者・発行元：Journal of Physics: Conference Series  

Positron emission tomography (PET) is a practical tool for range verification of hadron therapy. As well, the quantitative washout of the positron emitters has a potential usefulness as a diagnostic index, but the modelling for this has not been established. In this study, we measured washout rates of rabbit brain and performed kinetic analysis to explore the washout mechanism. Six rabbit brains were irradiated by 11C and 15O ion beams, and dynamic PET scan was performed using our original depth of interest (DOI)-PET prototype. The washout rate was obtained based on the two-compartment model, where efflux from tissue to blood (k2), influx (k3) and efflux (k4) from the first to second compartments in tissue were evaluated. The observed k2, k3 and k4 of 11C were 0.086, 0.137 and 0.007 min-1, and those of 15O were 0.502, 0.360 and 0.007 min-1, respectively. It was suggested permeability of a molecule containing 11C atoms might be regulated by a transporter. The k2 of 15O was comparable with 15O-water. This study provides basic data for modelling of the washout effect.

DOI： 10.1088/1742-6596/1662/1/012032

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Biomedical Physics and Engineering Express  

Although the luminescence of water at lower energy than the Cerenkov-light threshold during carbon-ion irradiation was found and imaging was possible, the temporal response has not been measured, and so the difference from Cerenkov-light remains unclear. To clarify this point, we measured the temporal response of the luminescence of water at lower energy than the Cerenkov-light threshold and compared it with that of Cerenkov-light. We used silicon photomultiplier (Si-PM) modules to measure the temporal response at the Bragg peak area of a water phantom during irradiation of the carbon ion where the Cerenkov-light was not included. We also measured the temporal response at the shallow depth of the water phantom where the Cerenkov-light was included. In both areas, we measured the temporal waveforms of the light produced by the irradiation of the carbon ions in which the ripples of spills were clearly observed. We found no difference in the waveforms between the Bragg peak and the shallow depths of water. Our results do not contradict the hypothesis that the luminescence of water and Cerenkov-light are produced by the same mechanism.

DOI： 10.1088/2057-1976/ab8b7e

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記述言語：日本語   出版者・発行元：Journal of Physics Communications  

Radioluminescence by protons and carbon ions of energy lower than the Cherenkov threshold (∼260 keV) in water has been observed. However, the origin of the luminescence has not been investigated well. In the present work, we imaged radioluminescence in water using synchrotron radiation that was of sufficiently lower energy (11 keV) than the Cherenkov threshold and we measured its spectrum using a high-sensitivity cooled CCD camera and optical longpass filters having 5 different thresholds. In addition, to determine effects of impurities in water, the water target was changed from ultrapure water to tap water. Monte Carlo simulation (Geant4) was also performed to compare its results with the experimentally obtained radioluminescence distribution. In the simulation, photons were generated in proportion to the energy deposition in water. As a result, the beam trajectory was clearly imaged by the radioluminescence in water. The spectrum was proportional to λ−3.4±0.4 under an assumption of no peaks. In the spectrum and distribution, no differences were observed between ultrapure water and tap water. TOC (total organic carbon) contents of ultrapure water and tap water as an impurity were measured and these were 0.26 mg l−1 and 2.3 mg l−1, respectively. The radioluminescence seemed to be attributable to water molecules not impurities. The radioluminescence distribution of the simulation was consistent with the experimental distribution and this suggested that radioluminescence was proportional to dose, which is expected to allow use for dose measurement.

DOI： 10.1088/2399-6528/ab9f8d

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Radiation Measurements  

The high-resolution imaging of alpha particles is required for the development of radio-compounds for targeted alpha-particle therapy or alpha emitter detection at nuclear facilities. Therefore, we developed an ultrahigh-resolution, real-time alpha-particle imaging system for observing the trajectories of alpha particles in a scintillator. The developed alpha-particle imaging system is made from a 1-μm-diameter fiber-structure scintillator plate that is optically coupled with the first of two sequentially connected tapered optical fiber plates. The output of the second, larger tapered optical fiber plate was imaged by an electron-multiplied (EM) cooled CCD camera. With our developed imaging system, we observed images of alpha particles having a spatial resolution of ~11 μm. We could also observe the trajectories of alpha particles with Bragg peaks for the angled incident alpha particles. We conclude that this imaging system, which can observe the trajectory of alpha particles in a fiber-structure scintillator, is promising for research on targeted alpha-particle therapy or alpha emitter detection at nuclear facilities.

DOI： 10.1016/j.radmeas.2020.106368

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physics in Medicine and Biology  

Positron emission tomography (PET) has been used for dose verification in charged particle therapy. The causes of washout of positron emitters by physiological functions should be clarified for accurate dose verification. In this study, we visualized the distribution of irradiated radioactive beams, 11C and 15O beams, in the rabbit whole-body using our original depth-of-interaction (DOI)-PET prototype to add basic data for biological washout effect correction. Time activity curves of the irradiated field and organs were measured immediately after the irradiations. All data were corrected for physical decay before further analysis. We also collected expired gas of the rabbit during beam irradiation and the energy spectrum was measured with a germanium detector. Irradiated radioactive beams into the brain were distributed to the whole body due to the biological washout process, and the implanted 11C and 15O ions were concentrated in the regions which had high blood volume. The 11C-labelled 11CO2 was detected in expired gas under the 11C beam irradiation, while no significant signal was detected under the 15O beam irradiation as a form of C15O2. Results suggested that the implanted 11C ions form molecules that diffuse out to the whole body by undergoing perfusion, then, they are incorporated into the blood-gas exchange in the respiratory system. This study provides basic data for modelling of the biological washout effect.

DOI： 10.1088/1361-6560/ab8532

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Radiation Measurements  

To ensure safe administration and quality assurance (QA) of scanning carbon-ion therapy doses, an efficient and reliable method to measure the lateral dose profile of a carbon-ion pencil beam, including the low-dose halo, is required. We developed a simple, expeditious dose measurement tool that employs a silver-activated zinc sulfide (ZnS) scintillator, which shows a low linear energy transfer (LET) dependency, to measure the low-dose halo of a carbon-ion pencil beam with high spatial resolution.

DOI： 10.1016/j.radmeas.2020.106299

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Medical Physics  

Purpose: To estimate relative biological effectiveness (RBE) ascribed to secondary fragments in a lateral distribution of carbon ion irradiation. The RBE was estimated with the microdosimetric kinetic (MK) model and measured linear energy transfer (LET) obtained with CR-39 plastic detectors. Methods: A water phantom was irradiated by a 12C pencil beam with energy of 380 MeV/u at the Gunma University Heavy Ion Medical Center (GHMC), and CR-39 detectors were exposed to secondary fragments. Because CR-39 was insensitive to low LET, we conducted Monte Carlo simulations with Geant4 to calculate low LET particles. The spectra of low LET particles were combined with experimental spectra to calculate RBE. To estimate accuracy of RBE, we calculated RBE by changing yield of low LET particles by ± 10% and ± 40%. Results: At a small angle, maximum RBE by secondary fragments was 1.3 for 10% survival fractions. RBE values of fragments gradually decreased as the angle became larger. The shape of the LET spectra in the simulation reproduced the experimental spectra, but there was a discrepancy between the simulation and experiment for the relative yield of fragments. When the yield of low LET particles was changed by ± 40%, the change in RBE was smaller than 10%. Conclusions: An RBE of 1.3 was expected for secondary fragments emitted at a small angle. Although, we observed a discrepancy in the relative yield of secondary fragments between simulation and experiment, precision of RBE was not so sensitive to the yield of low LET particles.

DOI： 10.1002/mp.13916

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physica Scripta  

High-intensity muon beams are now available at the Japan Proton Accelerator Research Complex and their use in radiotherapy may become possible in the future. Dose and range estimation are therefore important and optical imaging of the dose or range may be a promising method for that purpose. We calculated the dose and light distributions in water during irradiation of a positive muon beam using Monte Carlo simulation. First, we simulated the dose deposited in water for pencil beams with 30 and 50 MeV positive muons. We were able to clearly identify the Bragg peak in the depth dose profiles by muons and observed that the dose from positrons are added to the Bragg peak area with a ∼10% muon dose. We also found that the lateral dose widths increased as the depth increased and that it was ∼3-5 times wider at the Bragg peak position. With the light distribution of the muon in water, light produced by the positrons was dominant and distributed around the Bragg peak, and the peak positions were estimated within 2 mm differences of the peak position of the dose distributions. It is therefore possible to monitor the Bragg peak position of muons using an optical method.

DOI： 10.1088/1402-4896/ab3acb

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Radiation Measurements  

Precise measurement of the dose distribution of a carbon-ion pencil beam is essential for the safe delivery of treatment in scanned carbon-ion therapy. We developed an easy-to-use and quick dose-measurement tool that employs a silver-activated zinc-sulfide (ZnS) scintillator, which shows a smaller linear energy transfer (LET) dependency than conventional Gd-based scintillator, to measure the dose distribution of a carbon-ion pencil beam with high spatial resolution and small corrections. A ZnS scintillator sheet was set up perpendicular to the beam axis, and scintillation images were recorded using a charge-coupled device camera. We used 290-MeV/nucleon monoenergetic carbon-ion pencil beams at the Gunma University Heavy Ion Medical Center. The thickness of the water tank placed above the scintillator was remotely controlled to adjust the measurement depth. Images were acquired at different water depths, and the depth and lateral profiles were determined from the images. The results were compared with those of conventional Gd-based scintillator. The depth–light intensity profile of the ZnS scintillator matched the depth dose measured using an ionization chamber, which was better than that of a Gd-based scintillator. This result is advantageous for measurements using a carbon-ion pencil beam, which consists of primary carbon ions with a much higher LET than a proton, with smaller corrections. The ZnS scintillator showed good output characteristics, dose linearity (R2 > 0.99), and output reproducibility (deviations below 2%) and good agreement with the lateral-dose profiles measured using a diode down to ~1% of the central dose. The proposed tool can measure lateral profiles at the depth of the Bragg peak and tail in addition to the entrance. Our tool was used to quickly measure the dose distribution of carbon-ion pencil beam with high-spatial resolution and small corrections.

DOI： 10.1016/j.radmeas.2019.106207

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Biomedical Optics  

Although the luminescence of water at a lower energy than the Cerenkov-light (CL) threshold has been found for various types of radiation, the fractions of the luminescence of water to the total produced light have not been obvious for radiations at a higher energy than the CL threshold because it is difficult to separate these two types of light. Thus, we used a Monte Carlo simulation to estimate the fractions of the luminescence of water for various types of radiation at a higher energy than the CL threshold to confirm the major component of the produced light. After we confirmed that the estimated light production of the luminescence of water could adequately simulate the experimental results, we calculated the produced light photons of this luminescence and the CL from water for protons (170 MeV), carbon ions (330 MeV/n), high-energy x-ray (6 MV) from a linear accelerator (LINAC), high-energy electrons (9 MeV) from LINAC, positrons (F-18, C-11, O-15, and N-13), and high-energy gamma photon radionuclides (Co-60). For protons, the major fraction of the produced light was the luminescence of water in addition to the CL from the prompt gamma photons produced by the nuclear interactions. For carbon ions, the major fraction of the produced light was the luminescence of water and the CL produced by the secondary electrons in addition to the prompt gamma photons produced by the nuclear interactions. For high-energy x-ray and electrons from LINAC, the fractions of luminescence of water were 1/40.1 % to 0.2%. The fractions of luminescence of water for positrons were 0.2% to 1.5% and that for Co-60 was 0.4%. We conclude that the major fractions of light produced from x-ray and electrons from LINAC, positron radionuclides, and the Co-60 source are CL, with fractions of the luminescence of water from <0.1 % to 1.5%.

DOI： 10.1117/1.JBO.24.6.066005

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Radiation Measurements  

Measurements of three-dimensional (3D) dose distribution of electron-beams in water are important for high-energy electron beams from medical linear accelerators (LINAC). Although ionization chambers are commonly used for this purpose, measurements take a long time for precise 3D dose distribution. To solve the problem, we tried the measurements of the 3D dose distributions using a scintillator plate combined with a mirror. After we placed a 1 mm thick plastic scintillator plate at the upper inside of a black box, a water phantom was set above the plastic scintillator plate outside the black box, and electron beam was irradiated to the water phantom from the upper side. The attenuated electron-beam by the water in the phantom was detected by the plastic scintillator plate and the scintillation image was formed in the plate. The image was reflected by a surface mirror set below the plastic scintillator plate and detected by a cooled charge coupled device (CCD) camera from the side. We changed the depths of the water in the phantom, obtained the scintillation images, and calculated a 3D scintillation image using the measured images. Measurements were made for 9 MeV and 12 MeV electron-beams using the imaging system. From the images, we could successfully form 3D scintillation images. The depth profiles measured from the 3D images showed almost identical distribution with those calculated by the planning system within the difference of 5%. The lateral profiles also showed almost identical within the difference of the widths less than 2.5 mm. We conclude that the proposed method is promising for 3D dose distribution measurements of electron-beams.

DOI： 10.1016/j.radmeas.2019.04.002

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Radiation and Plasma Medical Sciences  

Because the sensitivity of positron emission tomography (PET) system increases in proportion to the inverse of the diameter of the detector ring, brain PET systems are being planned and developed. However, count losses due to the dead-time of the detector blocks increases as the ring diameter decreases. Since the count losses decrease the noise equivalent count rate (NECR) of the system, the NECR of brain PET system may be lower than that of a whole-body PET system in clinical dose range. In this paper, we compared the NECRs of brain PET systems with that of a whole-body PET system using a Monte Carlo simulation. We simulated the PET system for a 27-cm-diameter detector ring, a 54-cm-diameter detector ring, and an 89-cm-diameter detector ring and evaluated the NECRs. In the clinical dose range, the NECR of the small-diameter brain PET system was lower than those of the whole-body PET system unless the electronics was advanced. We conclude that the small-diameter brain PET system with conventional electronics has not so much advantage except for the lower cost and the higher spatial resolution. However, advanced electronics can reduce degradation of NECR, so the small-diameter brain PET system with advanced electronics will be useful for clinical studies.

DOI： 10.1109/TRPMS.2018.2876410

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Biomedical Physics and Engineering Express  

Because Cerenkov light is emitted above the threshold energy of the electrons (∼260 keV) in water and is emitted to forward directions, the light intensity distributions are different from the dose for x-ray and electron from LINAC. Cerenkov-light component was also observed with the depth profiles in carbon-ion. However the angular dependencies of the Cerenkov-light distributions were not obvious. Thus we calculated the depth profiles of the produced light distributions for 240 MeV n-1 carbon-ion, 6 MV x-ray, and 9 MeV electrons using Monte Carlo simulation. After we confirmed the simulation accuracies by comparing with the measured results, we calculated the depth profiles of luminescence of water and Cerenkov-light with various angles for these three types of radiations. With the simulation results, it became obvious that the depth profiles were significantly different with the angles for the produced light containing the Cerenkov-light. Cerenkov-light components were much higher at the larger angles. We also found the almost identical depth profile to dose with the angle of 10 degree to the right angle of the beam direction for 6 MV x-ray.

DOI： 10.1088/2057-1976/ab05b0

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physics in Medicine and Biology  

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.

DOI： 10.1088/1361-6560/aadaa6

Web of Science

Scopus

PubMed

記述言語：日本語   出版者・発行元：(公社)日本放射線技術学会  

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physics in Medicine and Biology  

Although luminescence of water lower in energy than the Cerenkov-light threshold during proton and carbon-ion irradiation has been found, the phenomenon has not yet been implemented for Monte Carlo simulations. The results provided by the simulations lead to misunderstandings of the physical phenomenon in optical imaging of water during proton and carbon-ion irradiation. To solve the problems, as well as to clarify the light production of the luminescence of water, we modified a Monte Carlo simulation code to include the light production from the luminescence of water and compared them with the experimental results of luminescence imaging of water. We used GEANT4 for the simulation of emitted light from water during proton and carbon-ion irradiation. We used the light production from the luminescence of water using the scintillation process in GEANT4 while those of Cerenkov light from the secondary electrons and prompt gamma photons in water were also included in the simulation. The modified simulation results showed similar depth profiles to those of the measured data for both proton and carbon-ion. When the light production of 0.1 photons/MeV was used for the luminescence of water in the simulation, the simulated depth profiles showed the best match to those of the measured results for both the proton and carbon-ion compared with those used for smaller and larger numbers of photons/MeV. We could successively obtain the simulated depth profiles that were basically the same as the experimental data by using GEANT4 when we assumed the light production by the luminescence of water. Our results confirmed that the inclusion of the luminescence of water in Monte Carlo simulation is indispensable to calculate the precise light distribution in water during irradiation of proton and carbon-ion.

DOI： 10.1088/1361-6560/aac74b

Web of Science

Scopus

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Biomedical Physics and Engineering Express  

In particle therapy, in-beam positron emission tomography (PET) is expected to enable in situ noninvasive confirmation of the treatment delivery. For accurate range and dose verification or three-dimensional (3D) volume imaging, however, correction of the biological washout effect in a living body is necessary. In this study, we measured the washout rate in a rabbit brain using the recently developed technology for oxygen beam radiation as well as carbon ion beam radiation. To measure components of washout, three radionuclides, 10C, 11C and 15O, which were generated as secondary beams in the Heavy Ion Medical Accelerator in Chiba (HIMAC), were irradiated on the rabbit brain under two conditions, live and dead. In-beam data were acquired by our whole body dual-ring OpenPET, which enables 3D in-beam imaging. Regions of interests (ROIs) were set as a 3D positron distribution and the time activity curves (TACs) of the irradiated field were acquired. We obtained the washout rate for those conditions based on multiple component model analysis. A difference between washout speed in 11C ions and the 15O ions was observed. The observed medium and slow biological decay rates of 11C ions in rabbit brain were 0.30 min-1 and 0.004 min-1, respectively. Those values were consistent with the previous rabbit study results acquired by other imaging modalities, such as the pair of positron cameras or our single-ring small animal OpenPET prototype. The observed medium and slow biological decay rates of 15O ions were 0.72 min-1 and 0.024 min-1, respectively, which were faster than those of the 11C ion. Also, the medium biological decay rate of 15O ions was close to the washout rate in cerebral blood flow (CBF) measurements by dynamic PET with 15O-labeled water. These results should help to establish an accurate washout correction model.

DOI： 10.1088/2057-1976/aaade7

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-6560/aaa453

Scopus

PubMed

出版者・発行元：Modern Rheumatology  

DOI： 10.1080/14397595.2017.1332558

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-6560/aa6644

Web of Science

PubMed

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0031-9155/61/13/4870

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0031-9155/61/5/1875

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s12194-016-0356-3

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0031-9155/59/7/1623

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s12194-013-0231-4

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0031-9155/58/23/8281

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0031-9155/58/5/1361

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s12149-011-0561-4

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/0031-9155/57/22/7481

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： https://doi.org/10.1080/18811248.2007.9711384

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）  

記述言語：英語   会議種別：口頭発表（一般）