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

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