研究者詳細 - 平野　祥之

論文 - 平野　祥之

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Effect of Cherenkov light on cell survival in x-ray irradiation of LINAC based on Monte Carlo simulation and cell survival measurements

Hirano, Y; Terada, Y

BIOMEDICAL PHYSICS & ENGINEERING EXPRESS 11 巻 ( 1 ) 2025年1月

記述言語：英語出版者・発行元：Biomedical Physics and Engineering Express

Cherenkov radiation is emitted during x-ray irradiation in a linear accelerator (LINAC). Cherenkov light contains many short wavelength components, including ultraviolet (UV) light, which is well-known for its bactericidal effects. A similar phenomenon is probable for human cancer cells. To assess the effect of Cherenkov light on cell death in x-ray irradiation, we employed simulations and UV cell survival data. We measured the survival rates of HeLa cells exposed to 254 nm (UVC) and 310 nm (UVB) light to determine the 50% lethal dose (LD50) required to kill 50% of the cells. For other wavelengths, we utilized literature values to establish the relationship between wavelength and LD50. Due to the broad range of the Cherenkov light spectrum, we need LD50 as a function of wavelength to estimate cell survival solely from Cherenkov light. A Monte Carlo simulation was used to calculate the fluence distribution of Cherenkov light in a 300 mm3 phantom comprised of soft tissue, both with and without absorption of visible light. The latter scenario is considered to be most influenced by Cherenkov light. By combining the fluence distribution and the wavelength-LD50 relationship, we determined the distribution of the survival rate. Our findings indicate that, in the absence of absorption, a radiation dose of approximately 90 Gy or greater is necessary for Cherenkov light to have any effect. As a result, the impact of Cherenkov light on cell survival can be considered negligible for typical dose of 2 Gy.

DOI： 10.1088/2057-1976/ad96c1

Estimation of produced oxygens in the track of heavy-ion using Geant4-DNA

Hirano, Y; Aso, T; Horii, Y

JOURNAL OF ADVANCED SIMULATION IN SCIENCE AND ENGINEERING 11 巻 ( 1 ) 頁： 207 - 221 2024年

Discrimination of inter-crystal scattering events by signal processing for the X'tal cube PET detector

Nitta, M; Nishikido, F; Inadama, N; Hirano, Y; Yamaya, T

RADIOLOGICAL PHYSICS AND TECHNOLOGY 16 巻 ( 4 ) 頁： 516 - 531 2023年10月

記述言語：英語出版者・発行元：Radiological Physics and Technology

Inter-crystal scattering (ICS) events cause degradation of the contrast in PET images. We developed the X’tal cube PET detector with submillimeter spatial resolution, which consisted of a segmented LYSO scintillator and 96 MPPCs. For this high spatial resolution PET detector, the ICS event was not negligible. In this study, we proposed a method to discriminate the ICS events and showed its feasibility by the following method. For each 96 MPPC, we measured the mean and standard deviation of the peak in the pulse height distribution obtained by the photoabsorption events in a scintillator pixel. Every time a newly detected event was identified as the segment, we monitored the reduced chi-square value that was calculated with the pulse height and the prepared mean and the standard deviation for each 96 MPPC. Since the pulse height caused by the photoabsorption event resulted in a small reduced chi-square value, we could eliminate the ICS events by setting a threshold on the reduced chi-square value. We carried out both a Monte Carlo simulation and a scanning experiment. By the simulation, we confirmed that the threshold of the reduced chi square significantly discriminated the ICS event. We obtained the response function by a scanning experiment with a 0.2 mm slit beam of 511 keV gamma-ray. The standard deviation of the response function was improved from 1.6 to 1.06 mm by eliminating the ICS events. The proposed method could significantly eliminate the ICS events and retain the true events.

DOI： 10.1007/s12194-023-00740-3

Dose distribution measurements using luminol water during irradiation of high-energy X-rays from medical linear accelerators (LINAC)

Yamamoto, S; Yamada, K; Yabe, T; Hirano, Y; Kataoka, J

RADIATION PHYSICS AND CHEMISTRY 208 巻 2023年7月

出版者・発行元：Radiation Physics and Chemistry

Dose distribution measurements of high-energy X-rays from a medical linear accelerator (LINAC) in water are important for quality control (QC) of the system, and Cherenkov-light imaging is an efficient method for measuring the high-energy X-ray dose distribution. However, the depth profiles have an underestimated dose at increased depths due to the angular dependency of the Cherenkov light. Luminol water is a possible material for measuring the dose distribution by detecting the light emitted from the chemical reaction with the reactive hydroxyl radical (・OH) produced in water by irradiation. In this study, we used luminol water for dose distribution measurements of high-energy X-rays from a LINAC. Imaging of the light emitted from luminol water was conducted using a cooled charge-coupled device (CCD) camera during irradiation with 6 MV X-rays from a LINAC to the luminol water. Imaging of the Cherenkov light in water was also conducted by irradiating 6 MV X-rays to water for correcting the Cerenkov-light component produced in luminol water. The Cherenkov-light image was subtracted from that of the luminol water to derive a dose image. The light emission of luminol water was ∼3 times higher than that of Cherenkov light in water. By subtracting the Cherenkov-light image from the luminol-water image, we could obtain an image that was identical to the dose distributions. The difference in the relative dose distribution was within −0.4% for the corrected image while that of the Cherenkov-light image was −7.9%. The multiple irradiations of luminol water with X-rays produced non-uniformity of emitted light, probably due to the production of hydrogen peroxide (H2O2) in water. We confirmed that imaging luminol water was promising for dose distribution imaging by correcting the Cherenkov-light component in the images. The non-uniformity of the emitted light by multiple irradiations in luminol water needs to be solved for more stable measurements.

DOI： 10.1016/j.radphyschem.2023.110895

Cherenkov-light imaging of induced positron distribution in liquid water after proton beam irradiation

Yamamoto, S; Yamashita, T; Kobashi, Y; Hirano, Y; Akagi, T; Yokokawa, H; Kataoka, J

JOURNAL OF INSTRUMENTATION 17 巻 ( 11 ) 2022年11月

出版者・発行元：Journal of Instrumentation

Imaging of positrons induced by nuclear reactions with a proton beam is a possible method for observing the beam shape from outside the subject. However, such imaging of induced positrons has so far been conducted for solid materials. The induced positron distribution in liquid water has not been measured or reported. To clarify the distribution of induced positrons in liquid water, we conducted Cherenkov-light imaging after irradiation by protons to a water phantom. After irradiation by a 117-MeV proton beam to a phantom containing liquid water, Cherenkov-light imaging of the induced positrons was conducted using a cooled charge-coupled device (CCD) camera following the decay of the positrons. We also imaged the luminescence of water during irradiation by the proton beam to compare the distributions. We could measure the distribution of Cherenkov-light from the induced positrons in liquid water. Positron distributions kept their beam shapes in water but were different from that of the luminescence image; positron distribution was wider in the deep area of the beams in the lateral as well as depth direction. The distributions' shapes were only slightly changed with time. We conclude that Cherenkov-light imaging from the induced positrons after irradiation by a proton beam in water was possible, and we found that the induced positrons kept their beam shape in water with different shape from that of dose. These findings may provide new insights for imaging in particle therapy.

DOI： 10.1088/1748-0221/17/11/P11043

Imaging of hydroxyl radical (.OH) distributions using luminol water during irradiation with low-energy X-rays

Yamamoto, S; Yabe, T; Hirano, Y; Kataoka, J

JOURNAL OF INSTRUMENTATION 17 巻 ( 10 ) 2022年10月

出版者・発行元：Journal of Instrumentation

Reactive hydroxyl radicals (·OH) play important roles in the biological effects of radiation exposure or radiation therapy, and the distribution of ·OH in water during irradiation is of interest to researchers. However, real-time ·OH distribution measurement during irradiation has so far not been achieved due to the difficulty of detecting ·OH. To make these distribution measurements possible, we attempted the imaging of light emitted from luminol water during irradiation with low-energy X-rays. Imaging of the light emitted from luminol water was conducted using a cooled charge-coupled device (CCD) camera during X-ray irradiation to luminol water at lower energy than the Cherenkov-light threshold. The light emission of luminol water was 25 times higher than that of water, and clear images of light distributions were measured for the luminol water. By carrying out the imaging of luminol water with the addition of a radical scavenger to the luminol water, we could confirm that the emitted light was from ·OH produced in water. With this addition of the radical scavenger, the light intensity decreased as the weight of the scavenger increased. With these results, we confirmed that the detected light distribution in luminol water could be attributed to the ·OH produced by the X-ray irradiation.

DOI： 10.1088/1748-0221/17/10/T10004

Correcting angular dependencies using non-polarized components of Cherenkov light in water during high-energy X-ray irradiation

Toyonaga, C; Yamamoto, S; Yabe, T; Okudaira, K; Yogo, K; Hirano, Y; Kataoka, J

MEDICAL PHYSICS 49 巻 ( 8 ) 頁： 5409 - 5416 2022年8月

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

Objective: Dose distribution measurements of high-energy X-rays from medical linear accelerators (LINAC) in water are important for quality control (QC) of the system. Although Cherenkov-light imaging is a useful method for measuring the high-energy X-ray dose distribution, depth profiles have an underestimated dose at increased depths due to the angular dependency of the Cherenkov light generated in water. In this study, we use a linear polarizer to separate the majority of polarized components from the majority of unpolarized components of Cherenkov-light images in water and then use this information to correct for angular dependencies. Methods: A water phantom, a cooled charge-coupled device (CCD) camera, and a polarizer were installed in a black box. Then, the water phantom was irradiated from the upper side with 6 or 10 MV X-rays, and the Cherenkov light generated in water was imaged with the polarizer axis at both parallel and perpendicular orientations to the beam. By using these images from the two orientations relative to the beam, we corrected the angular dependency of the Cherenkov light. Results: By subtracting the images measured with the polarizer perpendicular to the beams from the images measured with the polarizer parallel to the beams, we could obtain images with only the polarized components. Using these images, we could calculate the images with non-polarized components that had similar depth profiles to those calculated with a planning system. The average difference between corrected depth profiles and those calculated with the planning system was less than 1%, while that between uncorrected depth profiles and the planning system was more than 8.3% in depths of water from 20 to 100 mm. Conclusion: We conclude that the use of the polarizer has the potential to improve the accuracy of dose distribution in Cherenkov-light imaging of water using high-energy X-rays.

DOI： 10.1002/mp.15794

その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/mp.15794

Measurement of biological washout rates depending on tumor vascular status in <SUP>15</SUP>O in-beam rat-PET

Toramatsu, C; Mohammadi, A; Wakizaka, H; Sudo, H; Nitta, N; Seki, C; Kanno, I; Takahashi, M; Karasawa, K; Hirano, Y; Yamaya, T

PHYSICS IN MEDICINE AND BIOLOGY 67 巻 ( 12 ) 2022年6月

記述言語：英語出版者・発行元：Physics in Medicine and Biology

Objective. The biological washout of positron emitters should be modeled and corrected in order to achieve quantitative dose range verification in charged particle therapy based on positron emission tomography (PET). This biological washout effect is affected by physiological environmental conditions such as blood perfusion and metabolism, but the correlation to tumour pathology has not been studied yet. Approach. The aim of this study was to investigate the dependence of the biological washout rate on tumour vascular status in rat irradiation. Two types of tumour vascularity conditions, perfused and hypoxic, were modelled with nude rats. The rats were irradiated by a radioactive 15O ion beam and time activity curves were acquired by dynamic in-beam PET measurement. Tumour tissue sections were obtained to observe the histology as well. The biological washout rate was derived using a single-compartment model with two decay components (medium decay, k 2m and slow decay, k 2s ). Main results. All k 2m values in the vascular perfused tumour tissue were higher than the values of the normal tissue. All k 2m values in the hypoxic tumour tissue were much lower than the values of the vascular perfused tumour tissue and slightly lower than the values of the normal tissue. Significance. The dependency of the biological washout on the tumour vasculature conditions was experimentally shown.

DOI： 10.1088/1361-6560/ac72f3

Study on the DNA-damage by Tritium using Geant4-DNA simulation

Aso Tsukasa, Hara Masanori, Hirano Yoshiyuki

Transactions of Japanese Society for Medical and Biological Engineering Annual60 巻 ( Abstract ) 頁： 257_1 - 257_1 2022年

記述言語：英語出版者・発行元：Japanese Society for Medical and Biological Engineering

<p>Tritium is an isotope of hydrogen that emits very low energy beta-rays (18.6 keV maximum). The external exposure is limited while ingesting tritium in the body is considered to result in internal exposure. Such radiation damage in living cells is induced through DNA strand breaks (SBs) via direct and indirect effect. In this paper, we adopted the mechanistic approach of SBs by using an atomistic DNA model and a Monte Carlo simulation based on Geant4-DNA. The simulation includes physics interactions of beta-ray in water and subsequent chemical reactions of radicals in water radiolysis. The SB was assumed to occur if an energy was deposited beyond a certain threshold or if a hydroxyl radical approached inside phosphate or sugar sites in DNA-molecules. The results are discussed in the ratio of single strand breaks (SSBs) to double strand breaks (DSBs) with the contributions of direct and indirect effects.</p>

DOI： 10.11239/jsmbe.annual60.257_1

3-D Optical Imaging System of Muon Beams Using a Silver Activated Zinc Sulfide (ZnS(Ag)) Sheet Combined With a Mirror

Yamamoto, S; Ninomiya, K; Kawamura, N; Hirano, Y

IEEE TRANSACTIONS ON NUCLEAR SCIENCE 68 巻 ( 12 ) 頁： 2748 - 2752 2021年12月

記述言語：日本語出版者・発行元：IEEE Transactions on Nuclear Science

Optical imaging of muon beams is a promising method for range estimations. However, our previous optical imaging method could only measure 2-D projection images. To measure the beam ranges and widths at any position of the muon beam, 3-D beam images are desired. For this purpose, we developed an optical imaging system using a silver-activated zinc sulfide (ZnS(Ag)) sheet combined with a mirror and a cooled charge-coupled device (CCD) camera. The ZnS(Ag) sheet was set in a black box and irradiated by a positive muon beam at the Japan Proton Accelerator Research Complex (J-PARC). Acrylic plates were used to absorb the muon beam. The measured optical images with different thicknesses of the acrylic plates were stacked and interpolated to create a 3-D optical image, and then the depth and lateral profiles were evaluated. From the depth profile derived from the 3-D image, the Bragg peak position could be estimated. The lateral profiles at the Bragg peak positions could also be derived. We confirmed that 3-D optical imaging was possible using the developed system with a ZnS(Ag) sheet. The system is promising for measuring muon beam distribution, conducting research on muons, and developing future muon radiotherapy.

DOI： 10.1109/TNS.2021.3123164

Three-dimensional (3D) optical imaging of muon beam using a plastic scintillator plate in water

Yamamoto, S; Ninomiya, K; Kawamura, N; Yabe, T; Hirano, Y

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 1015 巻 2021年11月

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

Optical imaging of decayed positrons and muons with different collimators

Yamamoto, S; Ninomiya, K; Kawamura, N; Hirano, Y

JOURNAL OF INSTRUMENTATION 16 巻 ( 8 ) 2021年8月

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

Low background measurement in CANDLES-III for studying the neutrinoless double beta decay of <SUP>48</SUP>Ca

Ajimura, S; Chan, WM; Ichimura, K; Ishikawa, T; Kanagawa, K; Khai, BT; Kishimoto, T; Kino, H; Maeda, T; Matsuoka, K; Nakatani, N; Nomachi, M; Saka, M; Seki, K; Takemoto, Y; Takihira, Y; Tanaka, D; Tanaka, M; Tetsuno, K; Trang, VTT; Tsuzuki, M; Umehara, S; Akutagawa, K; Batpurev, T; Doihara, M; Katagiri, S; Kinoshita, E; Hirano, Y; Iga, T; Ishikawa, M; Ito, G; Kakubata, H; Lee, KK; Li, X; Mizukoshi, K; Moser, M; Ohata, T; Shokati, M; Uehara, T; Wang, W; Yamamoto, K; Yasuda, K; Yoshida, S; Yotsunaga, N; Harada, T; Hiraoka, H; Hiyama, T; Hirota, A; Ikeyama, Y; Kawamura, A; Kawashima, Y; Maeda, S; Nakajima, K; Ogawa, I; Ozawa, K; Shamoto, K; Shimizu, K; Shinki, Y; Tamagawa, Y; Tozawa, M; Yoshizawa, M; Fushimi, K; Hazama, R; Noithong, P; Rittirong, A; Suzuki, K; Iida, T

PHYSICAL REVIEW D 103 巻 ( 9 ) 2021年5月

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

A method to reduce the error due to the angular dependencies of Cerenkov-light in water for optical imaging of X-rays from high-energy medical linear accelerators (LINAC)

Toyonaga, C; Yamamoto, S; Hirano, Y; Okudaira, K; Kato, T; Sugita, K

JOURNAL OF INSTRUMENTATION 16 巻 ( 3 ) 2021年3月

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

Calculation of Stopping-Power Ratio from Multiple CT Numbers Using Photon-Counting CT System: Two- and Three-Parameter-Fitting Method

Lee, SH; Sunaguchi, N; Nagao, A; Hirano, Y; Sakurai, H; Kano, Y; Torikoshi, M; Kanai, T; Tashiro, M

SENSORS 21 巻 ( 4 ) 頁： 1 - 21 2021年2月

記述言語：英語出版者・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

Position distribution calculation of annihilation radiations and bremsstrahlung x rays in water during irradiation of positive muons: a Monte Carlo simulation study

Hirano, Y; Yamamoto, S; Kawamura, N; Ninomiya, K

PHYSICA SCRIPTA 96 巻 ( 2 ) 2021年2月

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

Imaging of polarized components of Cerenkov light and luminescence of water during carbon-ion irradiation 国際誌

Yamamoto, S; Yabe, T; Akagi, T; Hirano, Y

MEDICAL PHYSICS 48 巻 ( 1 ) 頁： 427 - 433 2021年1月

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: 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

Optical imaging of muons

Yamamoto, S; Ninomiya, K; Kawamura, N; Hirano, Y

SCIENTIFIC REPORTS 10 巻 ( 1 ) 頁： 20790 2020年12月

記述言語：英語出版者・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

Can B Washout Rate be a Biomarker of Tumor Viability in Charged Particle Therapy? A Rat In-beam PET Study

Toramatsu, C; Mohammadi, A; Wakizaka, H; Seki, C; Kanno, I; Karasawa, K; Hirano, Y; Yamaya, T

INTERNATIONAL JOURNAL OF RADIATION ONCOLOGY BIOLOGY PHYSICS 108 巻 ( 3 ) 頁： E254 - E254 2020年11月

Biological washout effect in in-beam PET: Animal studies

Toramatsu C., Mohammadi A., Wakizaka H., Seki C., Nishikido F., Sato S., Kanno I., Takahashi M., Karasawa K., Hirano Y., Yamaya T.

Journal of Physics: Conference Series 1662 巻 ( 1 ) 2020年10月

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

Measurements of temporal response of luminescence of water at lower energy than Cerenkov-light threshold during carbon-ion irradiation

Yamamoto, S; Akagi, T; Hirano, Y; Komori, M

BIOMEDICAL PHYSICS & ENGINEERING EXPRESS 6 巻 ( 4 ) 頁： 045002 2020年7月

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

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

Radioluminescence by synchrotron radiation with lower energy than the Cherenkov light threshold in water

Hirano, Y; Komori, M; Onoda, D; Nagae, T; Yamamoto, S

JOURNAL OF PHYSICS COMMUNICATIONS 4 巻 ( 7 ) 2020年7月

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

Development of an ultrahigh-resolution radiation real-time imaging system to observe trajectory of alpha particles in a scintillator

Yamamoto, S; Hirano, Y; Kamada, K; Yoshikawa, A

RADIATION MEASUREMENTS 134 巻 2020年6月

記述言語：英語掲載種別：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

Biological washout modelling for in-beam PET: rabbit brain irradiation by <SUP>11</SUP>C and <SUP>15</SUP>O ion beams

Toramatsu, C; Mohammadi, A; Wakizaka, H; Seki, C; Nishikido, F; Sato, S; Kanno, I; Takahashi, M; Karasawa, K; Hirano, Y; Yamaya, T

PHYSICS IN MEDICINE AND BIOLOGY 65 巻 ( 10 ) 頁： 105011 2020年5月

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

Scintillator screen for measuring low-dose halo in scanning carbon-ion therapy

Yogo, K; Tatsuno, Y; Souda, H; Matsumura, A; Tsuneda, M; Hirano, Y; Ishiyama, H; Saito, A; Ozawa, S; Nagata, Y; Nakano, T; Hayakawa, K; Kanai, T

RADIATION MEASUREMENTS 133 巻 2020年4月

記述言語：英語掲載種別：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

Estimations of relative biological effectiveness of secondary fragments in carbon ion irradiation of water using CR-39 plastic detector and microdosimetric kinetic model 査読有り

Hirano Y., Kodaira S., Souda H., Osaki K., Torikoshi M.

Medical Physics 47 巻 ( 2 ) 頁： 781 - 789 2020年2月

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

Estimation of dose and light distributions in water during irradiation of muon beams

Hirano, Y; Ninomiya, K; Yamamoto, S

PHYSICA SCRIPTA 94 巻 ( 12 ) 2019年12月

記述言語：英語掲載種別：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

Scintillator screen for measuring dose distribution in scanned carbon-ion therapy 査読有り

Yogo, K; Tatsuno, Y; Souda, H; Matsumura, A; Tsuneda, M; Hirano, Y; Ishiyama, H; Saito, A; Ozawa, S; Nagata, Y; Nakano, T; Hayakawa, K; Kanai, T

RADIATION MEASUREMENTS 129 巻 2019年10月

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

Estimation of the fractions of luminescence of water at higher energy than Cerenkov-light threshold for various types of radiation 国際誌

Hirano, Y; Yamamoto, S

JOURNAL OF BIOMEDICAL OPTICS 24 巻 ( 6 ) 頁： 1 - 9 2019年6月

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

Estimation of the three-dimensional (3D) dose distribution of electron beams from medical linear accelerator (LINAC) using plastic scintillator plate

Horita, R; Yamamoto, S; Yogo, K; Hirano, Y; Okudaira, K; Kawabata, F; Nakaya, T; Komori, M; Oguchi, H

RADIATION MEASUREMENTS 124 巻頁： 103 - 108 2019年5月

記述言語：英語掲載種別：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

Comparison of Noise Equivalent Count Rates (NECRs) for the PET Systems With Different Ring Diameter and Electronics

Nakanishi, K; Hirano, Y; Yamamoto, S

IEEE TRANSACTIONS ON RADIATION AND PLASMA MEDICAL SCIENCES 3 巻 ( 3 ) 頁： 371 - 376 2019年5月

記述言語：英語掲載種別：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

Angular dependencies of Cerenkov-light in water for carbon-ion, high energy x-ray and electron

Hirano, Y; Yamamoto, S

BIOMEDICAL PHYSICS & ENGINEERING EXPRESS 5 巻 ( 2 ) 2019年2月

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

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

Linear energy transfer (LET) spectra and survival fraction distribution based on the CR-39 plastic charged-particle detector in a spread-out Bragg peak irradiation by a <SUP>12</SUP>C beam

Hirano, Y; Kodaira, S; Souda, H; Matsumura, A; Torikoshi, M

PHYSICS IN MEDICINE AND BIOLOGY 63 巻 ( 18 ) 頁： 185006 2018年9月

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

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

陽子線、炭素線及びネオン線照射による水の発光効率のLET依存性

小森雅孝, 平野祥之, 矢部卓也, 堀田遼, 米内俊祐, 歳藤利行, 山本誠一

日本放射線技術学会雑誌 74 巻 ( 9 ) 頁： 1004 - 1004 2018年9月

Addition of luminescence process in Monte Carlo simulation to precisely estimate the light emitted from water during proton and carbon-ion irradiation

Yabe, T; Sasano, M; Hirano, Y; Toshito, T; Akagi, T; Yamashita, T; Hayashi, M; Azuma, T; Sakamoto, Y; Komori, M; Yamamoto, S

PHYSICS IN MEDICINE AND BIOLOGY 63 巻 ( 12 ) 頁： 125019 2018年6月

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

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

Washout effect in rabbit brain: In-beam PET measurements using <sup>10</sup>C, <sup>11</sup>C and <sup>15</sup>O ion beams

Toramatsu C., Yoshida E., Wakizaka H., Mohammadi A., Ikoma Y., Tashima H., Nishikido F., Kitagawa A., Karasawa K., Hirano Y., Yamaya T.

Biomedical Physics and Engineering Express 4 巻 ( 3 ) 2018年3月

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

A carbon CT system: how to obtain accurate stopping power ratio using a Bragg peak reduction technique.

Lee SH, Sunaguchi N, Hirano Y, Kano Y, Liu C, Torikoshi M, Ohno T, Nakano T, Kanai T

Physics in medicine and biology 63 巻 ( 3 ) 頁： 035025 2018年2月

Predictors of biologic discontinuation due to insufficient response in patients with rheumatoid arthritis who achieved clinical remission with biologic treatment: A multicenter observational cohort study

Asai Shuji, Fujibayashi Takayoshi, Oguchi Takeshi, Hanabayashi Masahiro, Hayashi Masatoshi, Matsubara Hiroyuki, Ito Takayasu, Yabe Yuichiro, Watanabe Tsuyoshi, Hirano Yuji, Kanayama Yasuhide, Kaneko Atsushi, Kato Takefumi, Takagi Hideki, Takahashi Nobunori, Funahashi Koji, Takemoto Toki, Asai Nobuyuki, Watanabe Tatsuo, Ishiguro Naoki, Kojima Toshihisa

MODERN RHEUMATOLOGY 28 巻 ( 2 ) 頁： 221 - 226 2018年

Influences of 3D PET scanner components on increased scatter evaluated by a Monte Carlo simulation. 査読有り

Hirano Y, Koshino K, Iida H

Physics in medicine and biology 62 巻 ( 10 ) 頁： 4017 - 4030 2017年5月

Induced radioactivity of a GSO scintillator by secondary fragments in carbon ion therapy and its effects on in-beam OpenPET imaging 査読有り

Hirano Y, Nitta M, Nishikido F, Yoshida E, Inadama N, Yamaya T

61 巻頁： 4870-89 2016年

Development of a DOI PET Detector Having the Structure of the X'tal Cube Extended in One Direction 査読有り

Inadama N, Hirano Y, Nishikido F, Murayama H, Yamaya T

IEEE Trans. On Nucl. Science 63 巻頁： 2509-16 2016年

Washout rate in rat brain irradiated by a 11C beam after acetazolamide loading using a small single-ring OpenPET prototype 査読有り

Hirano Y, Takuwa H, Yoshida E, Nisikido F, Nakajima Y, Wakizaka H, Yamaya T

Phys. Med. Biol 61 巻頁： 1875-87 2016年

After-pulsing, cross-talk, dark-count, and gain of MPPC under 7-T static magnetic field 査読有り

Hirano Y, Nishikido F, Kokuryo D, Yamaya T

Radiol. Phys. Technol. 9 巻頁： 245-53 2016年

Monte Carlo simulation of small OpenPET prototype with 11C beam irradiation: effects of secondary particles on in-beam imaging 査読有り

Hirano Y, Yoshida E, Kinouchi S, Nishikido F, Inadma N, Murayama H, Yamaya T

Phys. Med. Biol. 59 巻頁： 1623-40 2014年

Validation of using a 3-dimensional PET scanner during inhalation of 15O-labeld oxygen for quantitative assessment of reginal metabolic rate of oxygen in man 査読有り

Hori Y, Hirano Y, Koshino K, Moriguchi T, Iguchi S, Yamamoto A, Enmi J, Kawashima H, Zeniya T, Morita N, Nakagawara J, Casey ME, Iida H

Phys. Med. Biol 59 巻頁： 5593-609 2014年

X'tal cube PET detector composed of a stack of scintillator plates segmented by laser processing 査読有り

Inadama N, Moriya T, Hirano Y, Nishikido, F, Murayama H, Yoshida E, Tashima H, Nitta M, Ito H, Yamaya T

IEEE Trans. Nucl. Sci. 61 巻頁： 53-59 2014年

Efficient one-pair experimental system for spatial resolution demonstration of prototype PET detectors 査読有り

Tashima H, Yoshida E, Hirano Y, Nishikido F, Inadama N, Murayama H, Yamaya T

Radiol. Phys. Technol. 7 巻頁： 379-86 2014年

Positron annihilation spectroscopy of biological tissue in 11C irradiation 査読有り

Sakurai H, Itoh F, Hirano Y, Nitta M, Suzuki K, Kato D, Yoshida E, Nishikido F, Wakizaka H, Kanai T, Yamaya T

Phys. Med. Biol 59 巻頁： 7031-8 2014年

Performance evaluation of a depth-of-interaction detector by use of position-sensitive PMT with a super-bialkali photocathode 査読有り

Hirano Y, Nitta M, Inadama N, Nishikido F, Yoshida E, Murayama H, Yamaya T

Radiol. Phys. Technol 7 巻頁： 57-66 2014年

Compartmental analysis of washout effect in rat brain: in-beam OpenPET measurement using a 11C beam 査読有り

Phys. Med. Biol 58 巻頁： 8281-94 2013年

The X'tal cube PET detector with a monolithic crystal processed by the 3D sub-surface laser engraving technique: Performance comparison with glued crystal elements 招待有り査読有り

Yohida E, Hirano Y, Tashima, H, Inadama N, Nishikid 3F, Moriya T, Omura T, Watanabe M, Murayama H, Yamaya T

Ncul. Instrum. Methods. Phys Res. A 723 巻頁： 83-88 2013年

Spatial resolution limits for the isotropic-3D PET detector X'tal cube 査読有り

Yoshida E, Tashima H, Hirano Y, Inadama N, Nishikido F, Murayama H, Yamaya T

Ncul. Instrum. Methods. Phys Res., A 728 巻頁： 107-111 2013年

Development of a single-ring OpenPET prototype 査読有り

Yoshida E, Tashima, H, Wakizaka H, Nishikido F, Hirano Y, Inadama N, Murayama H, Ito H, Yamaya T

Ncul. Instrum. Methods. Phys Res. A 729 巻頁： 800-808 2013年

The X'tal cube PET detector with a monolithic crystal processed by the 3D sub-surface laser engraving technique: Performance comparison with glued 査読有り

Yoshida E, Hirano Y, Tashima H, Inadama N, Nishikido F, Moriya, T, Omura T, Watanabe M, Murayama H, Yamaya T

Ncul. Instrum. Methods. Phys Res., A 723 巻頁： 83–88 2013年

A proposal for PET/MRI attenuation correction with mu-values measured using a fixed-position radiation source and MRI segmentation 査読有り

Kawaguchi H, Hirano Y, Yoshida E, Jeff K, Suga M, Ikoma Y, Obata T, Ito H, Yamaya T,

Ncul. Instrum. Methods. Phys Res. A 734 巻頁： 156-61 2013年

Feasibility Study of an Axially Extendable Multiplex Cylinder PET 査読有り

Yoshida E, Hirano Y, Tashima H, Inadama N, Nishikido, F, Murayama H., Ito H, Yamaya, T

IEEE Trans. Nucl. Sci 50 巻頁： 3227-34 2013年

Impact of Laser-Processed X'tal Cube Detectors on PET Imaging in a One-Pair Prototype System. 査読有り

Yoshida E, Hirano Y, Tashima H, Inadama N, Nishikido F, Moriya T, Omura T, Watanabe M, Murayama H, Yamaya T

IEEE Trans. Nucl. Sci. 60 巻頁： 3172-80 2013年

Rapid quantitative CBF and CMRO2 measurements from a single PET scan with sequential administration of dual 15O-labeled tracers 査読有り

Kudomi N, Hirano Y, Koshino K, Hayashi T, Watabe H, Fukushima H, Moriwaki H, Teramoto N, Iihara K and Iida H

J. Cerb. Blood Flow Metab. 33 巻頁： 440-8 2013年

Potential for reducing the numbers of SiPM readout surfaces of laser-processed X'tal cube PET detectors 査読有り

Hirano Y, Inadama N, Yoshida E, Nishikido F, Murayama H, Watanabe M, Yamaya T

Phys. Med. Biol. 58 巻頁： 361-74 2013年

Monte Carlo estimation of scatter effects on quantitative myocardial blood flow and perfusable tissue fraction using 3D-PET and 15O-water. 査読有り

Hirano Y, Koshino K, Watabe H, Fukushima K, Iida H

Phys. Med. Boil 57 巻頁： 7481-92 2012年

Monte Carlo simulation of scintillation photons for the design of a high-resolution SPECT detector dedicated to human brain 査読有り

Hirano Y, Zeniya T, Iida H

Ann. Nucl. Med. 26 巻頁： 214-21 2012年

Effects of patient movement on measurements of myocardial blood flow and viability in resting 15O-water PET studies 査読有り

Koshino K, Watabe H, Enmi J, Hirano Y, Zeniya T, Hasegawa S, Hayashi T, Miyagawa S, Sawa Y, Hatazawa J, Iida H

J Nucl Cardiol. 19 巻頁： 524-78 2011年

Experimental pig model of old myocardial infarction with long survival leading to chronic left ventricular dysfunction and remodeling as evaluated by PET 査読有り

Teramoto N, Koshino K, Yokoyama I, Miyagawa S, Zeniya T, Hirano Y, Fukuda H, Enmi J, Sawa Y, Knuuti J, Iida H

J Nucl Med. 52 巻頁： 761-8 2011年

Preliminary Experiments on Accelerator-Driven Subcritical Reactor with Pulsed Neutron Generator in Kyoto University Critical Assembly 査読有り

Cheol Ho PYEON , Yoshiyuki HIRANO , Tsuyoshi MISAWA , Hironobu UNESAKI , Chihiro ICHIHARA , Tomohiko IWASAKI & Seiji SHIROYA

Journal of Nuclear Science and Technology 44 巻 ( 11 ) 頁： 1368-1378 2007年

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