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: Measurement of the dwell time and moving speed of a high-activity iridium-192 (Ir-192) source used for high-dose-rate (HDR) brachytherapy is important for estimating the precise dose delivery to a tumor. For this purpose, we used a cerium-doped yttrium aluminum perovskite (YA1O3:YAP(Ce)) gamma camera system, combined with a list-mode data acquisition system that can acquire short-time sequential images, and measured the dwell times and moving speeds of the Ir-192 source. Methods: Gamma photon imaging was conducted using the gamma camera in list mode for the Ir-192 source of HDR brachytherapy with fixed dwell times and positions. The acquired list-mode images were sorted to millisecond-order interval time sequential images to evaluate the dwell time at each position. Time count rate curves were derived to calculate the dwell time at each source position and moving speed of the source. Results: We could measure the millisecond-order time sequential images for the Ir-192 source. The measured times for the preset dwell times of 2 s and 10 s were 1.98 to 2.00 s full width at half maximum (FWHM) and 10.0 s FWHM, respectively. The dwell times at the first dwell position were larger than those at other positions. We also measured the moving speeds of the source after the dwells while moving back to the afterloader and found the speed increased with the distance from the edge of the field of view to the last dwell position. Conclusion: We conclude that millisecond-order time sequential imaging of the Ir-192 source is possible by using a gamma camera and is useful for evaluating the dwell times and moving speeds of the Ir-192 source.

DOI： 10.1002/mp.15957

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出版者・発行元：Journal of Instrumentation  

Although luminescence imaging of water during irradiation by particle ions is a promising method for dose estimation, it has only been tried for static images in which temporal information is not included. In addition to the positional distribution of the beam, temporal information is also important because the beams from a synchrotron-based therapy system have short pulse shapes called spills. The temporal information is also important for high dose rate, short-time radiotherapy, or so-called FLASH radiotherapy. To measure the particle ion beam distributions with precise temporal information, we conducted short time sequential luminescence imaging of protons. First, we measured short time sequential luminescence images during irradiation of a water phantom by 150-MeV protons using a cooled charge-coupled device (CCD) camera at 0.143-s intervals. With this imaging, the images showed beam distributions, but the shapes of the spill were not precisely evaluated in time intensity curves due to the insufficient sampling rate of the imaging. Then we measured short time sequential optical images with 0.053-s intervals. With this imaging, the images showed that the beam distributions in the spill shape could be measured, but the image and depth profiles evaluated from the images were noisy due to the insufficient light intensity. Consequently, we measured short time sequential luminescence images during irradiation of fluorescein (FS) water by 150-MeV protons. Since FS water produced ∼10 times higher luminescence, we could obtain high-intensity images enabling us to evaluate the time intensity curves based on the shape of the spills during measurement with 0.053-s intervals. The depth profiles of the beam were also obtained from the measured images. With these results, we confirmed that time sequential luminescence imaging was possible and, in such cases, FS water images measured at 0.053-s intervals are most promising to measure the short time sequential luminescence images during irradiation of protons.

DOI： 10.1088/1748-0221/17/12/T12001

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

Purpose: Although real-time imaging of the high-activity iridium-192 (Ir-192) source position during high-dose-rate (HDR) brachytherapy using a high-energy gamma camera system is a promising approach, the energy window was not optimized for spatial resolution or scatter fraction. Methods: By using a list-mode data-acquisition system that can acquire energy information of a cerium-doped yttrium aluminum perovskite (YA1O3: YAP(Ce)) gamma camera, we tried to optimize the energy window's setting to improve the spatial resolution and reduce scatter fraction. Results: The spatial resolution was highest for the central energy of the window at ∼300 keV. The scatter fraction was also smallest for the central energy of the window at ∼300 keV, and the scatter fraction was more than 48 % smaller than that for the full energy window. Conclusions: We clarified that the spatial resolution can be improved and the scatter fraction can be reduced through optimizing the energy window of the YAP(Ce) gamma camera by setting the central energy of the window to ∼300 keV for HDR brachytherapy.

DOI： 10.1016/j.ejmp.2022.09.017

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

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

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

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

Although optical imaging of electron beams and X-rays from medical linear accelerators (LINAC) is a possible method for dose distribution measurements, it has been limited to two-dimensional (2D) projection images. For the precise measurement of an optical image of electron beams and X-rays, three-dimensional (3D) imaging is desired. To measure 3D dose distributions, we conducted imaging of electron beams and X-rays using a plastic scintillator plate set in a water phantom. When this plate was immersed in the water phantom, irradiation with electron beams or X-rays 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 electron beams and X-rays. Measurements were conducted at 6 MeV, 9 MeV and 12 MeV for electron beams and at 6 MV and 10 MV for X-rays. The imaging system was set on the bed of the LINAC and moved at 10-mm steps perpendicular to the beam direction to acquire a set of sliced optical images of the beams. A set of these sliced images were stacked and interpolated to form 3D optical images. For the 3D images, after the correction of the Cherenkov-light component in the images, the relative depth and lateral doses were evaluated. From the relative depth doses of electron beams, the half-value depths could be evaluated within an error of 1.3 mm. Lateral widths could be evaluated within an error of less than 2 mm parallel to the plastic scintillator and less than 6.5 mm perpendicular to it. From the relative depth doses of X-rays, the average difference between the measured value and that by a planning system was within an error of 2 %. Lateral widths could be evaluated within an error of less than 0.68 mm parallel to the plastic scintillator and less than 2.6 mm perpendicular to it. We confirmed that 3D imaging of electron beams and X-rays using plastic scintillator plate is feasible and is a promising method for measuring dose images at any position.

DOI： 10.1088/1748-0221/17/08/P08015

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

Quality assurance (QA) of the source movement is essential for ensuring the safe delivery of high-dose-rate (HDR) brachytherapy. Here, we proposed a simple and effective method for real-time tracking of the source movement in high-dose-rate brachytherapy based on Cherenkov emission imaging. The Cherenkov light emitted from water irradiated by 192Ir-source γ-rays was captured using a high-sensitivity video camera. The source positions and dwell intervals were determined from the light images and compared with the preset values. The source dwell times and transit speeds were measured from the time course of the source positions. The brightness profiles were compared with the dose distributions provided by the treatment planning system. The source movements were visualized in real time as a movie of Cherenkov light emissions. The source positional intervals measured from the Cherenkov emission images agreed well to the preset values within 0.3 mm. The source dwell times were comparable to the preset values within 0.2 s, and the transit speeds were similar to those of previous reports. The brightness distributions agreed with the dose distributions within approximately 40%, except near the source center. The proposed Cherenkov method has good potential for tracking the source movement in real time in brachytherapy, as it could enable simultaneous measurements of the source positions, dwell times, and dose distributions.

DOI： 10.1088/1748-0221/17/07/T07001

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.3390/nano12050771

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担当区分：筆頭著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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 Research  

Radioprotectors with few side effects are useful for carbon-ion therapy, which directly induces clustering damage in DNA. With the aim of finding the most effective radioprotector, we investigated the effects of selected amino acids which might have chemical DNA-repair functions against therapeutic carbon ions. In the current study, we employed five amino acids: tryptophan (Trp), cysteine (Cys), methionine (Met), valine (Val) and alanine (Ala). Samples of supercoiled pBR322 plasmid DNA with a 17 mM amino acid were prepared in TE buffer (10 mM Tris, 1 mM ethylenediaminetetraacetic acid, pH 7.5). Phosphate buffered saline (PBS) was also used in assays of the 0.17 mM amino acid. The samples were irradiated with carbon-ion beams (290 MeV/u) on 6 cm spread-out Bragg peak at the National Institute of Radiological Sciences and Heavy Ion Medical Accelerator in Chiba, Japan. Breaks in the DNA were detected as changes in the plasmids and quantified by subsequent electrophoresis on agarose gels. DNA damage yields and protection factors for each amino acid were calculated as ratios relative to reagent-free controls. Trp and Cys showed radioprotective effects against plasmid DNA damage induced by carbon-ion beam, both in PBS and TE buffer, comparable to those of Met. The double-strand break (DSB) yields and protective effects of Trp were comparable to those of Cys. The yields of both single-strand breaks and DSBs correlated with the scavenging capacity of hydroxyl radicals (rate constant for scavenging hydroxyl radicals multiplied by the amino acid concentration) in bulk solution. These data indicate that the radioprotective effects of amino acids against plasmid DNA damage induced by carbon ions could be explained primarily by the scavenging capacity of hydroxyl radicals. These findings suggest that some amino acids, such as Trp, Cys and Met, have good potential as radioprotectors for preventing DNA damage in normal tissues in carbon-ion therapy.

DOI： 10.1667/RADE-21-00033.1

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/jrr/rrab036

PubMed

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

Purpose: We developed a novel and simple method to measure the source positions in applicators directly for high-dose-rate (HDR) brachytherapy based on Cherenkov emission imaging, and evaluated the performance. Methods: The light emission from plastic applicators used in cervical cancer treatments, irradiated by an 192Ir γ-ray source, was captured using a charge-coupled device camera. Moreover, we attached plastics of different shapes, including tapes, tubes, and plates to a metal applicator, to use as screens for the Cherenkov imaging. We determined the source positions and dwell intervals from the light profiles along with the applicator and compared these with preset values and dummy marker measurements. Results: The source positions and dwell intervals measured from the light images were comparable to the dummy marker measurements and preset values. The distance from the applicator tip to the first source positions agreed with the dummy marker measurements within 0.2 mm for the plastic tandem. The dwell intervals measured using the Cherenkov method agreed with the preset values within 0.6 mm. The distances measured with three plastic types on the metal applicator also agreed with the dummy marker measurements within 0.2 mm. The dwell intervals measured using the plastic tape agreed with the preset values within 0.7 mm. Conclusions: The proposed method should be suitable for rapid and easy quality assurance (QA) investigations in HDR brachytherapy, as it enables source position using a single image. The method allows for real-time, filmless measurements of the source positions to be obtained and is useful for rapid feedback in QA procedures.

DOI： 10.1002/mp.14606

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：International Journal of Nanomedicine  

Purpose: Gold nanoparticles (AuNPs) are candidate radiosensitizers for medium-energy photon treatment, such as γ-ray radiation in high-dose-rate (HDR) brachytherapy. However, high AuNP concentrations are required for sufficient dose enhancement for clinical applica-tions. Here, we investigated the effect of positively (+) charged AuNP radiosensitization of plasmid DNA damage induced by 192Ir γ-rays, and compared it with that of negatively (−) charged AuNPs. Methods: We observed DNA breaks and reactive oxygen species (ROS) generation in the presence of AuNPs at low concentrations. pBR322 plasmid DNA exposed to 64 ng/mL AuNPs was irradiated with 192Ir γ-rays via HDR brachytherapy. DNA breaks were detected by observing the changes in the form of the plasmid and quantified by agarose gel electro-phoresis. The ROS generated by the AuNPs were measured with the fluorescent probe sensitive to ROS. The effects of positively (+) and negatively (−) charged AuNPs were compared to study the effect of surface charge on dose enhancement. Results: +AuNPs at lower concentrations promoted a comparable level of radiosensitization by producing both single-stranded breaks (SSBs) and double-stranded breaks (DSBs) than those used in cell assays and Monte Carlo simulation experiments. The dose enhancement factor (DEF) for +AuNPs was 1.3 ± 0.2 for SSBs and 1.5 ± 0.4 for DSBs. The ability of +AuNPs to augment plasmid DNA damage is due to enhanced ROS generation. While −AuNPs generated similar ROS levels, they did not cause significant DNA damage. Thus, dose enhancement using low concentrations of +AuNPs presumably occurred via DNA binding or increasing local +AuNP concentration around the DNA. Conclusion: +AuNPs at low concentrations displayed stronger radiosensitization compared to −AuNPs. Combining +AuNPs with 192Ir γ-rays in HDR brachytherapy is a candidate method for improving clinical outcomes. Future development of cancer cell-specific +AuNPs would allow their wider application for HDR brachytherapy.

DOI： 10.2147/IJN.S292105

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

DOI： 10.1667/RR15502.1

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.radmeas.2020.106299

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1038/s41598-020-60519-z

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.radmeas.2019.106227

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.radmeas.2019.106207

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.radmeas.2019.106128

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/2057-1976/ab169e

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/acm2.12601

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.radmeas.2019.04.002

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.meddos.2017.12.006

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/acm2.12226

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.ejmp.2017.06.022

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1361-6560/aa67cc

PubMed

DOI： 10.1016/j.apradiso.2013.12.

担当区分：筆頭著者  

DOI： 10.1016/S0375-9601(02)01324-5