Progress in Medical Physics (한국의학물리학회지:의학물리)

Korean Society of Medical Physics (한국의학물리학회)
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Feasibility Study of the microDiamond Detector for Measurement of Small Field Photon Beam

광자선 소조사면 선량측정을 위한 microDiamond 검출기의 유용성 고찰

  • Lee, Chang Yeol (Department of Radiation Oncology, College of Medicine, Inha University) ;
  • Kim, Woo Chul (Department of Radiation Oncology, College of Medicine, Inha University) ;
  • Kim, Hun Jeong (Department of Radiation Oncology, College of Medicine, Inha University) ;
  • Ji, Young Hoon (Research Institute of Radiological and Medical Sciences, Korea Institute of Radiological and Medical Sciences) ;
  • Kim, Kum Bae (Research Institute of Radiological and Medical Sciences, Korea Institute of Radiological and Medical Sciences) ;
  • Lee, Sang Hoon (Department of Radiation Oncology, College of Medicine, Kwandong University) ;
  • Min, Chul Kee (Department of Radiation Oncology, College of Medicine, Soonchunhyang University) ;
  • Jo, Gwang Hwan (Department of Radiation Oncology, College of Medicine, Soonchunhyang University) ;
  • Shin, Dong Oh (Department of Radiation Oncology, College of Medicine, Kyunghee University) ;
  • Kim, Seong Hoon (Department of Radiation Oncology, College of Medicine, Hanyang University) ;
  • Huh, Hyun Do (Department of Radiation Oncology, College of Medicine, Inha University)
  • 이창열 (인하대학교 의과대학 방사선종양학교실) ;
  • 김우철 (인하대학교 의과대학 방사선종양학교실) ;
  • 김헌정 (인하대학교 의과대학 방사선종양학교실) ;
  • 지영훈 (한국원자력의학원 방사선의학연구소) ;
  • 김금배 (한국원자력의학원 방사선의학연구소) ;
  • 이상훈 (관동대학교 의과대학 방사선종양학교실) ;
  • 민철기 (순천향대학교 의과대학 방사선종양학교실,) ;
  • 조광환 (순천향대학교 의과대학 방사선종양학교실,) ;
  • 신동오 (경희대학교 의과대학 방사선종양학교실) ;
  • 김성훈 (한양대학교 의과대학 방사선종양학교실) ;
  • 허현도 (인하대학교 의과대학 방사선종양학교실)
  • Received : 2014.11.11
  • Accepted : 2014.11.28
  • Published : 2014.12.30
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Abstract

The dosimetry of very small fields is challenging for several reasons including a lack of lateral electronic equilibrium, large dose gradients, and the size of detector in respect to the field size. The objective of this work was to evaluate the suitability of a new commercial synthetic diamond detector, namely, the PTW 60019 microDiamond, for the small field dosimetry in cyberknife photon beams of 6 different collimator size (from 5 mm to 30 mm). Measurements included dose linearity, dose rate dependence, output factors (OF), percentage depth doses (PDD) and off center ratio (OCR). The results were compared to those of pinpoint ionization chamber, diamond detector, microLion liquid Ionization chamber and diode detector. The dose linearity results for the microDiamond detector showed good linearly proportional to dose. The microDiamond detector showed little dose rate dependency throughout the range of 100~600 MU/min, while microLion liquid Ionization chamber showed a significant discrepancy of approximately 5.8%. The OF measured with microDiamond detector agreed within 3.8% with those measured with diode. PDD curves measured with silicon diode and diamond detector agreed well for all the field sizes. In particular, slightly sharper penumbras are obtained by the microDiamond detector, indicating a good spatial resolution. The results obtained confirm that the new PTW 60019 microDiamond detector is suitable candidate for application in small radiation fields dosimetry.

소조사면을 이용하는 방사선치료기법들은 소조사면내의 측면 전자 비평형, 급격한 선량 변화, 그리고 조사면 크기에 대한 검출기의 기하학적 크기 영향으로 정확한 선량의 평가가 어렵다. 본 연구의 목적은 사이버나이프의 6개의 조사면(5 mm~30 mm)에 대해서 소조사면 선량측정용으로 새롭게 출시되어 상업적으로 이용되고 있는 마이크로다이아몬드(PTW 60019 microDiamond) 검출기의 유용성을 평가하고자 한다. 이를 위해 선량선형성, 선량률의존성, 출력선량계수, 깊이선량백분율 및 축바깥선량비 등의 선량측정인자를 측정하였고, 0.015 cc 부피의 이온전리함(PTW 31014 PinPoint chamber), 다이아몬드 검출기(PTW 60003 diamond), 액체이온함(PTW 31018 microLion), 그리고 다이오드 검출기(PTW 60008 diode)의 측정 결과와 비교 및 평가를 하였다. 그 결과 마이크로다이아몬드 검출기는 선량선형성이 우수하며, 선량률의존성이 적게 나타났다. 또한 사이버나이프 소조사면 측정용으로 상업적으로 권고되고 있는 다이오드 검출기와의 선량측정인자 측정값 3.8%의 차이를 보였다. 또한 깊이선량백분율도 다이오드 검출기의 결과와 유사한 결과를 얻었다. 마이크로다이아몬드 검출기는 유효체적이 작으므로 반음영이 작게 평가되었으며, 다른 검출기들보다도 공간분해능이 높은 것으로 생각된다. 연구 결과 마이크로다이아몬드 검출기는 조직등가물질로 이루어져 있으며, 작은 유효체적으로 광자선 소조사면선량측정 검출기로서 매우 유용한 것으로 판단된다.

Keywords

References

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