Journal of radiological science and technology (대한방사선기술학회지:방사선기술과학)

Korean Society of Radiological Science (대한방사선과학회)
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Evaluation of Image Quality for Various Electronic Portal Imaging Devices in Radiation Therapy

방사선치료의 다양한 EPID 영상 질평가

  • Son, Soon-Yong (Department of Radiology, Asan Medical Center) ;
  • Choi, Kwan-Woo (Department of Radiology, Asan Medical Center) ;
  • Kim, Jung-Min (Department of College of Health Science, Radiologic Science, Korea University) ;
  • Jeong, Hoi-Woun (Department of Radiological Technology, Baekseok Culture University) ;
  • Kwon, Kyung-Tae (Department of Radiological Technology, Dongnam Health University) ;
  • Cho, Jeong-Hee (Department of Radiation Oncology, Yonsei Medical Center) ;
  • Lee, Jea-Hee (Department of Radiation Oncology, Seoul National University Hospital) ;
  • Jung, Jae-Yong (Department of Radiation Oncology, Sanggye Paik Hospital) ;
  • Kim, Ki-Won (Department of Radiology, Kyung Hee University Hospital at Gang-dong) ;
  • Lee, Young-Ah (Department of Bio-Technologist and Laboratory Animal, Shingu University College) ;
  • Son, Jin-Hyun (Department of Radiological Technology, Shingu University College) ;
  • Min, Jung-Whan (Department of Radiological Technology, Shingu University College)
  • 손순룡 (서울아산병원 영상의학과) ;
  • 최관우 (서울아산병원 영상의학과) ;
  • 김정민 (고려대학교 방사선학과) ;
  • 정회원 (백석문화대학교 방사선과) ;
  • 권경태 (동남보건대학교 방사선과) ;
  • 조정희 (연세대학교 신촌세브란스 종양학과) ;
  • 이제희 (서울대학교병원 종양학과) ;
  • 정재용 (상계백병원 종양학과) ;
  • 김기원 (강동경희대병원 영상의학과) ;
  • 이영아 (신구대학교 바이오 동물학과) ;
  • 손진현 (신구대학교 방사선과) ;
  • 민정환 (신구대학교 방사선과)
  • Received : 2015.10.31
  • Accepted : 2015.12.21
  • Published : 2015.12.31
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Abstract

In megavoltage (MV) radiotherapy, delivering the dose to the target volume is important while protecting the surrounding normal tissue. The purpose of this study was to evaluate the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE) using an edge block in megavoltage X-ray imaging (MVI). We used an edge block, which consists of tungsten with dimensions of 19 (thickness) ${\times}$ 10 (length) ${\times}$ 1 (width) $cm^3$ and measured the pre-sampling MTF at 6 MV energy. Various radiation therapy (RT) devices such as TrueBeam$^{TM}$ (Varian), BEAMVIEW$^{PLUS}$ (Siemens), iViewGT (Elekta) and Clinac$^{(R)}$iX (Varian) were used. As for MTF results, TrueBeam$^{TM}$(Varian) flattening filter free(FFF) showed the highest values of $0.46mm^{-1}$ and $1.40mm^{-1}$ for MTF 0.5 and 0.1. In NPS, iViewGT (Elekta) showed the lowest noise distribution. In DQE, iViewGT (Elekta) showed the best efficiency at a peak DQE and $1mm^{-1}DQE$ of 0.0026 and 0.00014, respectively. This study could be used not only for traditional QA imaging but also for quantitative MTF, NPS, and DQE measurement for development of an electronic portal imaging device (EPID).

MV방사선 치료는 둘러싸여 있는 정상조직의 피폭선량을 최소화 하면서, target volume 내에 정확하게 선량을 전달하는데 있어 중요한 요인이다. 본 연구에서는 방사선 치료의 높은 정확성을 유지하기 위하여 megavoltage X-ray imaging (MVI)에서 edge block 을 사용한 digital radiography (DR) system 검출기의 modulation transfer function (MTF: 변조전달함수), the noise power spectrum (NPS: 잡음전력스펙트럼) and the detective quantum efficiency (DQE: 양자검출효율)를 측정하고자 한다. 우리는 텅스텐으로 구성된 19 (thickness) ${\times}$ 10 (length) ${\times}$ 1 (width) $cm^3$의 edge block을 사용하였으며, 다음과 같은 setting들로 pre-sampling modulation transfer function (MTF)를 계산하였다: 6-megavolt (MV) energy를 사용하고, 다양한 Radiotherapy장비인 TrueBeamTM (Varian), BEAMVIEWPLUS (Siemens), iViewGT (Elekta), ClinacR iX (Varian) 를 사용하였다. MTF결과에서 Varian TrueBeamTM flattening filter free가 MTF의 50% ($mm^{-1}$)에서 0.46, 10% ($mm^{-1}$) 에서 1.40로 가장 highest value를 보였다. Noise 분포는 Elekta iViewGT가 가장 낮은 분포를 보였다. DQE에서는 E lekt a iViewGT가 peak DQE에서 0.0026 그리고 $1mm^{-1}$ DQE 에서 0.00014로 가장 높았다. 본 연구는 Edge method를 이용하여 MTF와 DQE산출을 재현하였으며, 현재 임상에서 사용되는 DR 시스템 측정의 높은 정확성을 유지할 수 있었으며 이러한 연구는 전통적인 QA 영상화뿐만 아니라 검출기 개발 연구에 있어서 정량적인 MTF, NPS, DQE 측정에 더욱 더 효율적으로 사용될 수 있다는 것을 알 수 있다.

Keywords

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