Faculty Profiles - KOYAMA Shuji

Papers - KOYAMA Shuji

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モンテカルロシミュレーションの応用-CT領域- Invited

小山修司

日本放射線技術学会雑誌 Vol. 71 ( 4 ) page： 371-379 2015.4

Authorship：Lead author Language：Japanese

放射線医療において吸収線量を評価する場合の基本は,測定器を用いた実測であることはいうまでもない.いろいろなモダリティや X 線照射の状況の中で, 多くの場合,実測値があればそれで十分評価が可能である.ところが,場合によっては,実測が困難であるとか,不可能な状況が存在する.この場合に有効なのが,モンテカルロシミュレーションである.例えば, マンモグラフィ撮影において,乳腺組織と脂肪組織が混在する場合の乳腺組織だけの吸収線量を求める場合などがそれに相当する.この場合,実際に乳房に入射する X 線の空気カーマから平均乳腺線量を求める係数は,モンテカルロシミュレーションによって求められたものである1).X 線 CT についても,少し手の込んだ線量評価を行う場合,モンテカルロシミュレーションは非常に有効なツールとなる.
モンテカルロシミュレーションには,研究者自身が一から作成するものと,物理現象を組み込んだ計算のエンジン部分が用意されていてそこにユーザが任意のシミュレーション体系や線源情報を作成して合体する汎用モンテカルロコードがある.汎用モンテカルロシミュレーションコードには,有名な Geant や MCNP, 純国産の Phits などがあるが,われわれは低エネルギー放射線の計算精度が高い汎用モンテカルロシミュレーションコード Electron Gamma Shower 5(EGS5)2) を使用しており,ここでは,この EGS5 についてと, その X 線 CT での応用について述べる.

DOI： 10.6009/jjrt.2015_JSRT_71.4.371

A Monte Carlo simulation based on measured tube current modulation data in X-ray computed tomogramphy

Masaki Inoue, Shuji Koyama, Tomonobu Haba, Tomoki Shibahara

Proceedings of the Twenty-Second EGS User's Meeting in Japan page： 14-17 2015

Regional brain activity during jaw clenching with natural teeth and with occlusal splints: a preliminary functional MRI study Reviewed

ARIJI Yoshiko, KOYAMA Shuji, SAKUMA Shigemitsu, NAKAYAMA Miwa, ARIJI Eiichirou

The Journal of Craniomandibular & Sleep Practice 2015

Language：English Publishing type：Research paper (scientific journal)

Objective: The purpose of this study was to investigate regional brain activity during jaw clenching with natural teeth and with two types of occlusal splints using functional magnetic resonance imaging (fMRI). Methods: Sixteen healthy volunteers were enrolled in this study. Blood oxygenation level-dependent (BOLD) fMRI signals were compared under three conditions: during clenching with natural teeth, with a soft splint, and with a hard splint. For each condition, 30-second jaw clenching followed a 60-second rest, and was repeated three times, with intervening 30-second rests. SPM 8 was used for the fMRI analysis.
Results: Blood oxygenation level-dependent signals during clenching with natural teeth increased in BA44, 45, and the cerebellum. Blood oxygenation level-dependent signals increased in those areas and in BA17, 18 during clenching with a soft splint. Use of the hard splint increased the BOLD signals in BA6 and BA20, 37 in addition to the areas previously mentioned. Blood oxygenation level-dependent signals in the left BA6, the left BA20, 37, and the right BA44, 45 were significantly higher during clenching with a hard splint than with natural teeth. These regions are associated with motor coordination, memory, and cognition, respectively.

DOI： 10.1179/2151090315Y.0000000017

Relationship between the tube voltage dependence of cross-sectional absorbed profile and exposed dose of superficial radiosensitive organs

Tomoki Shibahara, Shuji Koyama, Masaki Inoue, Tomonobu Haba

Proceedings of the Twenty-Second EGS User's Meeting in Japan page： 19-24 2015

Language：English Publishing type：Research paper (scientific journal)

There has been a growing concern regarding exposure to superficial radiosensitive organs with the rapid increase of computed tomography examinations. Manufacturers have been developing various dose reduction methods in order to prevent harm to these organs. Our previous study revealed a unique phenomenon in X-ray computed tomography scanning, in which the maximum absorbed dose position shifts to a deeper region from the surface in a water cylindrical phantom. We considered that this result could be applied as a dose reduction method. Therefore, in this study, we investigate the tube voltage dependence of this unique phenomenon. The results show that the peak dose position shifts to a deeper region with increasing tube voltage. The superficial radiosensitive organs can thus be protected from peak dose exposure by adjusting the tube voltage.

DOI： 19-24

DRシステムにおけるDQE測定時の各因子の測定精度に関する検討 Reviewed

國友博史，小山修司，東出了，市川勝弘，服部真澄，岡田陽子，林則夫，澤田道人

日本放射線技術学会雑誌 Vol. 70 ( 7 ) page： 653-661 2014.7

Language：Japanese Publishing type：Research paper (scientific journal)

診断用X線装置におけるDQE測定にかかわる誤差因子とその影響について検討を行った．4種類のX線装置を用いてX線エネルギースペクトル測定に基づいた検討による光子数の推定結果から，IEC法の規定光子数は妥当であることが示された．また間接変換型FPDにおいてRQA5の線質を中心に約±5kVの範囲で，NNPSの誤差は1%以下に収まり，ある程度の管電圧誤差が許容されることが示された.また．NNPS測定における IEC法の規定する面積外の測定は，X線量子数分布の不均一による影響からDQEを過小評価する可能性が示唆された．また，エッジ法のMTF測定においては，天板上配置による拡大率の影響は無視できず，エッジデバイスと検出器との密着性の必要性が明らかとなった．

DOI： 10.6009/jjrt.2014_JSRT_70.7.653

フラットパネルディテクタによる3Dローテーションアンギオグラフィ，コーンビーム CTの被ばく線量評価 Reviewed

瀬口繁信，西條貴哉，石川芳信，小山修司

日本放射線技術学会雑誌 Vol. 70 ( 7 ) page： 646-652 2014.7

Language：Japanese Publishing type：Research paper (scientific journal)

フラットパネルアンギオクラフィ装置による3D回転アンギオグラフィとコーンビームCTにおける組織・臓器線量測定を，人体ファントムに埋め込まれた半導体線量計により行った．これを16列MDCTと比較したところ，脳の位置の臓器線量では，コーンビームCTでMDCTの約半分の25mGy程度，３D回転アンギオグラフィではMDCTの約15分の1の3.5mGyとなった．また，放射線感受性の高い水晶体を避けるような軌道を設定することが，放射線防護に非常に有用であることが示された．

DOI： 10.6009/jjrt.2014_JSRT_70.7.646

Influence of difference in cross-sectional dose profile in a CTDI phantom on X-ray CT dose estimation : a Monte Carlo study Reviewed

HABA Tomonobu, KOYAMA Shuji, IDA Yoshihiro

Radiation Physics and Technology Vol. 7 ( 1 ) page： 133-140 2014.1

Accuracy validation of incident photon fluence on DQE for various measurement conditions and X-ray units Reviewed

HABA Tomonobu, KONDO Shimpei, HAYASHI Daiki, KOYAMA Shuji

Radiation Physics and Technology Vol. 6 ( 2 ) page： 423-430 2013.6

Investigation of Backscatter Factor in Mammography using EGS5

NUMAMOTO Hitomi, ISHII Takanori, HIRAI Yuta, KOYAMA Shuji

Proceedings of the Twentieth EGS Users' Meeting in Japan page： in press 2013

Verification of In-phantom X-ray Energy Spectra in Dual-Energy Computed Tomography

ISHII Takanori, NUMAMOTO Hitomi, HIRAI Yuta, KOYAMA Shuji

Proceedings of the Twentieth EGS Users' Meeting in Japan page： in press 2013

Estimation of glandular dose distribution in mammography using EGS5

NUMAMOTO Hitomi, HABA Tomonobu, KONDO Shinpei. HAYASHI Daiki. ISHII Takanori, KOYAMA Shuji

Proceedings of the Nineteenth EGS Users' Meeting in Japan page： 53-57 2012.10

Language：English Publishing type：Research paper (scientific journal)

The aim of this research is to analyze the absorbed dose distribution by changes of thickness of subcutaneous adipose and target-filter combination in mammography using EGS5. Assume the mammography examination, x-ray tube voltage, compression plate, breast model phantom, and image receptor were included in EGS5 code. That breast model phantom had various thicknesses of subcutaneous adipose. Our results showed that absorbed dose was a tendency to increase with thinning of the subcutaneous adipose thickness. It indicated that average glandular dose (AGD) that is recently used could have been underestimated. Also relative absorbed dose of glandular tissues tended to be low when the energy of incident x-ray became large. It indicated that target/filter combinations have strong effect to incident x-ray supectrum, so that we must choose most proper target/filter combinations that reduce the radiation dose while maintaining image contrast.

Reduction of Radiation Dose to Children in X-Ray Head CT : Investigation Using EGS5

ISHII Takanori, KONDO Shinpei, HABA Tomonobu, HAYASHI Daiki, NUMAMOTO Hitomi, KOYAMA Shuji

Proceedings of the Nineteenth EGS Users' Meeting in Japan page： 48-52 2012.10

Language：English Publishing type：Research paper (scientific journal)

In this study, the absorbed dose for organs in infant, child, and adult patients undergoing head computed tomography (CT) scans was determined. The CT examinations were simulated using the Electron Gamma Shower ver. 5 (EGS5) Monte Carlo code. The eye lens dose among child and infant patients was higher than that among adult patients by 15.0% and 69.7%, respectively. The effectiveness of a bismuth shield in reducing the eye lens dose for children undergoing head X-ray head CT scans was also evaluated. Application of a bismuth shield over the eyes of children undergoing head X-ray CT reduced the eye lens dose by 47.6% from the dose value in the case wherein shielding was not used. The use of metallic shields was found effective in reducing the radiation dose to children.

Verification of the effect of dose reduction system in computed tomography - Evaluation of organ and tissue dose distribution using EGS5 simulation -

HAYASHI Daiki, KOYAMA Shuji

Proceedings of the Nineteenth EGS Users' Meeting in Japan page： 41-47 2012.10

Language：English Publishing type：Research paper (scientific journal)

Computed tomography auto exposure control (CT-AEC) is designed to reduce exposed radiation dose and to equalize overall image quality in X-ray CT. This study aims to validate the dose reduction effect of CT-AEC with dose distribution maps created in an anthropomorphic phantom using the Electron Gamma Shower ver. 5 (EGS5) Monte Carlo simulation code. Further we actually measured the absorbed doses of each organ and tissue in the phantom with and without CT-AEC. The organ doses in the simulation result were in good agreement with the measurement results. The dose reduction effect was assessed by a comparison of dose distribution maps with and without CT-AEC. In conclusion, the results of this study revealed that the combination of dosimetry in anthropomorphic phantoms and calculation by simulation enables a detail assessment of the dose reduction effect of CT-AEC.

Verification of Pin-photo Diode Detector Characteristics Using EGS5

KONDO Shimpei, HABA Tomonobu, HAYASHI Daiki, NUMAMOTO Hitomi, ISHII Takanori, KOYAMA Shuji

Proceedings of the Nineteenth EGS Users' Meeting in Japan page： 16-20 2012.10

Language：English Publishing type：Research paper (scientific journal)

We developed a novel X-ray beam analyzing system with eight sensors using commercially available pin silicon photodiodes to estimate the effective energy and intensity of incident X-ray in each angle undergoing computerized tomography (CT). The aim of this study was to verify characteristics of photodiodes of X-ray beam analyzing system in a diagnostic energy region using Electron Gamma Shower ver.5 (EGS5). X-ray energy and angular dependence were assessed for the X-ray beam analyzing system by irradiating one of eight sensors, and which were also calculated by EGS5 under the same conditions as those considered during the measurement. Measurement results is that the output value of photodiode was correlated with any effective energy of incident X-rays, which suggested that when a sensor in the X-ray beam analyzing system is irradiated, the system can estimate the effective energy of the incident X-rays. X-ray energy and angular dependence calculated by EGS5 are in good agreement with measurement, which can be helpful in further experiments. In this study, the characteristics of photodiodes of X-ray beam analyzing system were obtained through measurement experiment, and were verified by EGS5. X-ray beam analyzing system can accurately estimate the effective energy of any incident X-rays which has any maximum energy and the shape of X-ray energy spectra.

Effectiveness of the message passing interface method in reducing computation time

HABA Tomonobu, KONDO Shimpei, HAYASHI Daiki, TAKEUCHI Akihiko, ISHII Takanori, NUMAMOTO Hitomi, KOYAMA Shuji

Proceedings of the Nineteenth EGS Users' Meeting in Japan page： 1-3 2012.10

Language：English Publishing type：Research paper (scientific journal)

In this study, we validated the effectiveness of using a message passing interface (MPI) method in reducing computation time and enhancing calculation accuracy. A chest and abdominal X-ray computed tomography scan was simulated. Our results indicated that the MPI method was accurately incorporated into the Electron Gamma Shower ver. 5 (EGS5) MC code. The MPI method could reduce computation time from 34 hours to 6 hours. We believe that MC simulation is going to be used widely. Therefore, incorporating the MPI method into EGS5 is very useful for EGS5 users.

診断X線検査による乳幼児，小児，成人の被ばく線量 — X線単純撮影の場合 Reviewed

青山隆彦，小山修司，川浦稚代，杉本成人，藤井啓輔，川崎稔生

保健物理 Vol. 47 ( 2 ) page： 130-140 2012.6

2種類の歯科用コーンビームCTの吸収線量と実効線量に関する検討 Reviewed

岡野恒一，松尾綾江，後藤賢一，横井みどり，蛭川亜紀子，奥村信次，小山修司

日本放射線技術学会雑誌 Vol. 68 ( 3 ) page： 216-225 2012.3

Comparison of Radiation Doses between Newborns and 6-y-old Children undergoing Head, Chest and Abdominal CT Examinations - a Phantom Study Reviewed

SUGIMOTO Naruto, AOYAMA Takahiko, KOYAMA Shuji, YAMAUCHI-KAWAURA Chiyo, FUJII Keisuke

Radiation Protection Dosimetry 2012

Organ Dose and Effective Dose Estimation in Paediatric Chest Radiographic Examinations by Using PIN Silicon Photodiode Dosemeters Reviewed

KAWASAKI Toshio, AOYAMA Takahiko, YAMAUCHI-KAWAURA Chiyo, FUJII Keisuke, KOYAMA Shuji

Radiation Protection Dosimetry 2012

Evaluation of Maximum Dose Position Shifting in Phantom in X-ray CT Reviewed

HABA Tomonobu, KOYAMA Shuji

Progress in NUCLEAR and TECHNOLOGY ( 3 ) page： 72-75 2012

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