研究者詳細 - 余語　克紀

Development and performance evaluation of a thin GAGG:Ce scintillator plate for high resolution synchrotron radiation X-ray imaging 査読有り Open Access

Yoshino, M; Yamamoto, S; Nakanishi, K; Yogo, K; Kamada, K; Koshikawa, N; Kataokac, J; Yoshikawaa, A

JOURNAL OF INSTRUMENTATION 19 巻 ( 10 ) 頁： P10030 - P10030 2024年10月

掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Instrumentation

Scintillator-based X-ray imaging detectors are pivotal in numerous scientific and practical domains, including medical imaging, food and device inspection, and security monitoring. Recent advancements have spurred interest in 4D X-ray imaging using synchrotron radiation, necessitating higher temporal resolutions. Consequently, this places stringent demands on X-ray detector technology, especially when X-ray energy exceeds 20 keV. The selection of a suitable scintillator material is crucial for achieving optimal timing resolution, yet it poses a significant challenge in dynamic X-ray imaging. This study delves into the optimization of scintillator properties and their impact on spatial resolution and light output, elucidating the performance of Ce-doped Gd3Ga3Al2O12 (GAGG:Ce) scintillators for X-ray imaging applications. We developed a micro X-ray imaging detector using a 100 μm-thick GAGG:Ce scintillator plate and conducted X-ray imaging tests at the Aichi SR facility. The results demonstrated that the resolution, quantified as the chart slit width at a contrast transfer function (CTF) value of 10%, reached 2 ∼ 3 μm with a 4× lens, 0.52 μm± 0.03 μm with a 20× lens, and 0.42 μm± 0.01 μm with a 40× lens. Although the results of this study did not achieve a spatial resolution nearing the effective pixel size of the 40× lens, the text also elucidates the underlying reasons for this limitation. Furthermore, we compared the X-ray sensitivity of our GAGG:Ce scintillator plate with that of a commercial LuAG:Ce scintillator, revealing an approximately 1.5-fold increase in light output. As a demonstration, transmission images of dried small fish were captured using the GAGG:Ce scintillator plate and the developed X-ray imaging system. These findings highlight the potential of the X-ray imaging detector devised in this study for future generations of X-ray imaging applications.

DOI： 10.1088/1748-0221/19/10/P10030

その他リンク： https://iopscience.iop.org/article/10.1088/1748-0221/19/10/P10030/pdf

A comparative study of EM-CCD and CMOS cameras for particle ion trajectory imaging 査読有り

Yamamoto, S; Yoshino, M; Nakanishi, K; Yogo, K; Kamada, K; Yoshikawa, A; Kataoka, J

APPLIED RADIATION AND ISOTOPES 204 巻頁： 111143 - 111143 2024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：Applied Radiation and Isotopes

High-resolution and real-time imaging of particle ion trajectories is essential in nuclear medicine and nuclear engineering. One potential method to achieve high-resolution real-time trajectory imaging of particle ions involves utilizing an imaging system that integrates a scintillator plate with a magnifying unit and a cooled electron multiplying charge-coupled device (EM-CCD) camera. However, acquiring an EM-CCD camera might prove challenging due to the discontinuation of CCD sensor manufacturing by vendors. As an alternative imaging approach, a low-noise, high-sensitivity camera utilizing a cooled complementary metal-oxide-semiconductor (CMOS) sensor offers a promising solution for imaging particle ion trajectories. Yet, it remains uncertain whether CMOS-based cameras can perform as effectively as CCD-based cameras in capturing particle ion trajectories. To address these concerns, we conducted a comparative analysis of the imaging performance between a CMOS-based system and an EM-CCD-based system for capturing alpha particle trajectories. The results revealed that both systems could image the trajectories of alpha particle, but the spatial resolution with the CMOS-based camera exceeded that of the EM-CCD-based camera, primarily due to the smaller pixel size of the sensor. While the signal-to-noise ratio (SNR) of the trajectory image from the CMOS-based camera initially lagged behind that from the EM-CCD-based camera, this disparity was mitigated by implementing binning techniques on the CMOS-based camera images. In conclusion, our findings suggest that a cooled CMOS camera could serve as a viable alternative for imaging particle ion trajectories.

DOI： 10.1016/j.apradiso.2023.111143

Estimating blurless and noise-free Ir-192 source images from gamma camera images for high-dose-rate brachytherapy using a deep-learning approach 査読有り

Nakanishi, K; Yamamoto, S; Yabe, T; Yogo, K; Noguchi, Y; Okudaira, K; Kawachi, N; Kataoka, J

BIOMEDICAL PHYSICS & ENGINEERING EXPRESS 10 巻 ( 1 ) 2024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：Biomedical Physics and Engineering Express

Objective. Precise monitoring of the position and dwell time of iridium-192 (Ir-192) during high-dose-rate (HDR) brachytherapy is crucial to avoid serious damage to normal tissues. Source imaging using a compact gamma camera is a potential approach for monitoring. However, images from the gamma camera are affected by blurring and statistical noise, which impact the accuracy of source position monitoring. This study aimed to develop a deep-learning approach for estimating ideal source images that reduce the effect of blurring and statistical noise from experimental images captured using a compact gamma camera. Approach. A double pix2pix model was trained using the simulated gamma camera images of an Ir-192 source. The first model was responsible for denoising the Ir-192 images, whereas the second model performed super resolution. Trained models were then applied to the experimental images to estimate the ideal images. Main results. At a distance of 100 mm between the compact gamma camera and the Ir-192 source, the difference in full width at half maximum (FWHM) between the estimated and actual source sizes was approximately 0.5 mm for a measurement time of 1.5 s. This difference has been improved from approximately 2.7 mm without the use of DL. Even with a measurement time of 0.1 s, the ideal images could be estimated as accurately as in the 1.5 s measurements. This method consistently achieved accurate estimations of the source images at any position within the field of view; however, the difference increased with the distance between the Ir-192 source and the compact gamma camera. Significance. The proposed method successfully provided estimated images from the experimental images within errors smaller than 0.5 mm at 100 mm. This method is promising for reducing blurring and statistical noise from the experimental images, enabling precise real-time monitoring of Ir-192 sources during HDR brachytherapy.

DOI： 10.1088/2057-1976/ad0bb2

その他リンク： https://iopscience.iop.org/article/10.1088/2057-1976/ad0bb2/pdf

Sub-micrometer real-time imaging of trajectory of alpha particles using GAGG plate and CMOS camera 査読有り

Yamamoto, S; Yoshino, M; Nakanishi, K; Yogo, K; Kamada, K; Yoshikawa, A; Koshikawaa, N; Kataokaa, J

JOURNAL OF INSTRUMENTATION 18 巻 ( 10 ) 頁： T10003 - T10003 2023年10月

掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Instrumentation

High-resolution and real-time imaging of the trajectories of alpha particles is desired in nuclear medicine and nuclear engineering. Although an imaging method using a scintillator plate combined with a magnifying unit and a cooled electron multiplying charge-coupled device (EM-CCD) camera is a possible method of obtaining high-resolution trajectory images, the spatial resolution of the system is limited to ∼2 μm. To overcome the spatial resolution limitations of this method on trajectory imaging, we used a cooled complementally metal oxide (CMOS) camera in which the sensor had a much larger number of pixels, which were also smaller. Using the CMOS camera based imaging system, we could measure the trajectories of alpha particles in real time with the spatial resolution of 0.34 μm FWHM. With smoothing of the images to reduce image noise, spatial resolution was still kept to less than 0.75 μm. We conclude that this CMOS camera-based alpha-particle trajectory-imaging system is promising for alpha-particle or other particles imaging where ultrahigh spatial resolution is required.

DOI： 10.1088/1748-0221/18/10/T10003

その他リンク： https://iopscience.iop.org/article/10.1088/1748-0221/18/10/T10003/pdf

Luminescence imaging of water irradiated by protons under FLASH radiation therapy conditions 査読有り国際誌

Yogo Katsunori, Kodaira Satoshi, Kusumoto Tamon, Kitamura Hisashi, Toshito Toshiyuki, Iwata Hiromitsu, Umezawa Masumi, Yamada Masashi, Miyoshi Takuto, Komori Masataka, Yasuda Hiroshi, Kataoka Jun, Yamamoto Seiichi

PHYSICS IN MEDICINE AND BIOLOGY 68 巻 ( 15 ) 2023年8月

担当区分：筆頭著者,　責任著者記述言語：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

Objective. FLASH radiation therapy with ultrahigh dose rates (UHDR) has the potential to reduce damage to normal tissue while maintaining anti-tumor efficacy. However, rapid and precise dose distribution measurements remain difficult for FLASH radiation therapy with proton beams. To solve this problem, we performed luminescence imaging of water following irradiation by a UHDR proton beam captured using a charge-coupled device camera. Approach. We used 60 MeV proton beams with dose rates of 0.03-837 Gy s−1 from a cyclotron. Therapeutic 139.3 MeV proton beams with dose rates of 0.45-4320 Gy s−1 delivered by a synchrotron-based proton therapy system were also tested. The luminescent light intensity induced by the UHDR beams was compared with that produced by conventional beams to compare the dose rate dependency of the light intensity and its profile. Main results. Luminescence images of water were clearly visualized under UHDR conditions, with significantly shorter exposure times than those with conventional beams. The light intensity was linearly proportional to the delivered dose, which is similar to that of conventional beams. No significant dose-rate dependency was observed for 0.03-837 Gy s−1. The light-intensity profiles of the UHDR beams agreed with those of conventional beams. The results did not differ between accelerators (synchrotron or cyclotron) and beam energies. Significance. Luminescence imaging of water is achievable with UHDR proton beams as well as with conventional beams. The proposed method should be suitable for rapid and easy quality assurance investigations for proton FLASH therapy, because it facilitates real-time, filmless measurements of dose distributions, and is useful for rapid feedback.

添付ファイル： 0712広報修正_PressRelease0614Proton1y3.pdf

DOI： 10.1088/1361-6560/ace60b

Short-time sequential high-energy gamma photon imaging using list-mode data acquisition system for high-dose-rate brachytherapy 査読有り

[展望・解説] 放射線治療「せめる/まもる」薬剤の探索；輪ゴム DNAの損傷評価査読有り

余語克紀

放射線化学 ( 115 ) 2023年4月

Nagata Jura, Yamamoto Seiichi, Yabe Takuya, Yogo Katsunori, Nakanishi Kohei, Noguchi Yumiko, Okudaira Kuniyasu, Kamada Kei, Yoshikawa Akira, Kataoka Jun

MEDICAL PHYSICS 49 巻 ( 12 ) 頁： 7703 - 7714 2022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：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

Short time sequential luminescence imaging of water during irradiation by protons 査読有り

Yamamoto Seiichi, Yabe Takuya, Yogo Katsunori, Akagi Takashi, Kataoka Jun

JOURNAL OF INSTRUMENTATION 17 巻 ( 12 ) 2022年12月

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

Optimization of the energy window setting in Ir-192 source imaging for high-dose-rate brachytherapy using a YAP(Ce) gamma camera 査読有り

Nagata Jura, Nakanishi Kohei, Yamamoto Seiichi, Yabe Takuya, Yogo Katsunori, Noguchi Yumiko, Okudaira Kuniyasu, Kamada Kei, Yoshikawa Akira, Kataoka Jun

PHYSICA MEDICA-EUROPEAN JOURNAL OF MEDICAL PHYSICS 103 巻頁： 66 - 73 2022年11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 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

Three-dimensional (3D) optical imaging of electron beam and X-rays from medical linear accelerators (LINAC) using a plastic scintillator plate in water 査読有り

Yamamoto Seiichi, Hiramatsu Airi, Shimizu Yui, Yabe Takuya, Yogo Katsunori, Kataoka Jun

JOURNAL OF INSTRUMENTATION 17 巻 ( 8 ) 2022年8月

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

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

Toyonaga Chihiro, Yamamoto Seiichi, Yabe Takuya, Okudaira Kuniyasu, Yogo Katsunori, Hirano Yoshiyuki, Kataoka Jun

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

Three-dimensional (3D) optical imaging of electron beam and X-rays from medical linear accelerators (LINAC) using a plastic scintillator plate in water 査読有り

Seiichi Yamamoto, Airi Hiramatsu, Yui Shimizu, Takuya Yabe, Katsunori Yogo, Jun Kataoka

Journal of Instrumentation 17 巻頁： P08015 2022年8月

Real-time tracking of source movement by Cherenkov emission imaging for high-dose-rate brachytherapy 査読有り

Yogo K., Tatsuno Y., Shimo T., Noguchi Y., Okudaira K., Nozawa M., Ishiyama H., Yasuda H., Oguchi H., Yamamoto S.

JOURNAL OF INSTRUMENTATION 17 巻 ( 7 ) 2022年7月

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

Radiosensitization Effect of Gold Nanoparticles on Plasmid DNA Damage Induced by Therapeutic MV X-rays 査読有り

Yogo Katsunori, Misawa Masaki, Shimizu Hidetoshi, Kitagawa Tomoki, Hirayama Ryoichi, Ishiyama Hiromichi, Yasuda Hiroshi, Kametaka Satoshi, Takami Seiichi

NANOMATERIALS 12 巻 ( 5 ) 頁： 771 - 771 2022年3月

総説「プラスミドDNA損傷を指標とした放射線保護剤/増感剤の探索-放射線治療併用のアミノ酸と金ナノ粒子を中心として-」招待有り査読有り

余語克紀、平山亮一、保田浩志、三澤雅樹

放射線生物研究 56 巻 ( 3 ) 頁： 260 - 279 2021年9月

Protective Effects of Amino Acids on Plasmid DNA Damage Induced by Therapeutic Carbon Ions 査読有り国際誌

Yogo Katsunori, Murayama Chieko, Hirayama Ryoichi, Matsumoto Ken-ichiro, Nakanishi Ikuo, Ishiyama Hiromichi, Yasuda Hiroshi

RADIATION RESEARCH 196 巻 ( 2 ) 頁： 197 - 203 2021年8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 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

Three-dimensional dose-distribution measurement of therapeutic carbon-ion beams using a ZnS scintillator sheet. 査読有り国際誌

Yogo K, Tsuneda M, Horita R, Souda H, Matsumura A, Ishiyama H, Hayakawa K, Kanai T, Yamamoto S

Journal of radiation research 2021年5月

Source position measurement by Cherenkov emission imaging from applicators for high-dose-rate brachytherapy. 査読有り国際誌

Yogo K, Noguchi Y, Okudaira K, Nozawa M, Ishiyama H, Okamoto H, Yasuda H, Oguchi H, Yamamoto S

Medical physics 48 巻 ( 1 ) 頁： 488 - 499 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: 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

Effect of Gold Nanoparticle Radiosensitization on Plasmid DNA Damage Induced by High-Dose-Rate Brachytherapy 査読有り国際誌

Yogo Katsunori, Misawa Masaki, Shimizu Morihito, Shimizu Hidetoshi, Kitagawa Tomoki, Hirayama Ryoichi, Ishiyama Hiromichi, Furukawa Takako, Yasuda Hiroshi

INTERNATIONAL JOURNAL OF NANOMEDICINE 16 巻頁： 359 - 370 2021年

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