콘빔 전산화단층촬영(CBCT) 시스템에서 기계적 오류에 관한 연구

A Study on Mechanical Errors in Cone Beam Computed Tomography(CBCT) System

  • 이이성 (안양 샘병원 방사선종양학과) ;
  • 유은정 (안양 샘병원 방사선종양학과) ;
  • 김승근 (안양 샘병원 방사선종양학과) ;
  • 최경식 (안양 샘병원 방사선종양학과) ;
  • 이정우 (건국대학교병원 방사선종양학과) ;
  • 서태석 (서울가톨릭의과대학대학원 의공학교실) ;
  • 김정구 (한서대학교 방사선학과)
  • Lee, Yi-Seong (Department of Radiation Oncology, Anyang SAM Hospital) ;
  • Yoo, Eun-Jeong (Department of Radiation Oncology, Anyang SAM Hospital) ;
  • Kim, Seung-Keun (Department of Radiation Oncology, Anyang SAM Hospital) ;
  • Choi, Kyoung-Sik (Department of Radiation Oncology, Anyang SAM Hospital) ;
  • Lee, Jeong-Woo (Department of Radiation Oncology, Konkuk University Medical Center) ;
  • Suh, Tae-Suk (Department of Biomedical Engineering and Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea) ;
  • Kim, Joeng-Koo (Department of Radiological Science, Hanseo University)
  • 투고 : 2013.02.26
  • 심사 : 2013.06.07
  • 발행 : 2013.06.30

초록

본 연구는 선형가속기의 회전불균형의 영향으로 발생 되는 CBCT 영상의 setup 오차 변화를 분석하여, 회전불균형에 대한 정도관리의 필요성을 연구 하였다. CBCT 시스템의 3차원 체적영상모드를 이용하여 $360^{\circ}$ 회전과 $180^{\circ}$ 회전으로 Catphan503 팬텀과 균질 팬텀의 3차원 영상을 획득하였고, setup 오차를 측정하기 위해 나선형 CT의 기준영상과 함께 비교 분석 하였다. 표준 정도관리의 절차를 시행하여 정상적인 상태를 확인하고, 임의적으로 갠트리의 회전균형을 조절한 후, 균형상태와 불균형상태의 각각 CBCT 영상에 대하여 X, Y, Z, Roll, Pitch, and Yaw의 6차원적 관점에서 setup 오차를 측정하고 분석하였다. Setup 오차의 변화율은 갠트리 회전균형의 조정 전 후를 확인한 결과, 직교 좌표계는 $360^{\circ}$의 회전에서 X축 방향으로 0.6 mm, Y축 방향으로 0.5 mm, Z축 방향으로 0.5 mm의 최대 변화율을 보였다. $180^{\circ}$의 회전은 X축 방향으로 0.9 mm, Y축 방향은 0.2 mm, Z축 방향은 0.3 mm의 최대 변화율을 보였다. 또한 회전 변환계는 회전 불균형이 커질수록 평균적인 값의 차이가 점점 증가하였고, 최대값은 $1.1^{\circ}$를 나타내었다. 영상의 분해능은 균형 조정 전 후 영상분석 툴에서 2 lp/cm 차이를 나타내었다. CBCT 시스템의 정도관리는 기준 권고안을 만족하였다. 갠트리의 회전 불균형이 클 때, setup 오차의 직교 좌표계의 변화는 크지 않았으나, 회전 변환계의 변화율은 기준 권고 값인 $1^{\circ}$에 해당하는 값과 초과하는 $1.1^{\circ}$를 나타내었다. 이는 갠트리의 불균형이 setup 오차에 영향을 미치는 것을 알 수 있었으며, 또한 회전 변환계의 setup 오차에 대한 6차원적인 보정이 더욱 요구됨을 알 수 있다. 그러므로 정확하고 정교한 영상유도 방사선치료를 수행하기 위해서는 갠트리의 균형도를 확인해야 하며, 정도관리 항목으로 추가되어야 한다고 사료되어진다.

This study investigated the rate of setup variance by the rotating unbalance of gantry in image-guided radiation therapy. The equipments used linear accelerator(Elekta Synergy TM, UK) and a three-dimensional volume imaging mode(3D Volume View) in cone beam computed tomography(CBCT) system. 2D images obtained by rotating $360^{\circ}$and $180^{\circ}$ were reconstructed to 3D image. Catpan503 phantom and homogeneous phantom were used to measure the setup errors. Ball-bearing phantom was used to check the rotation axis of the CBCT. The volume image from CBCT using Catphan503 phantom and homogeneous phantom were analyzed and compared to images from conventional CT in the six dimensional view(X, Y, Z, Roll, Pitch, and Yaw). The variance ratio of setup error were difference in X 0.6 mm, Y 0.5 mm Z 0.5 mm when the gantry rotated $360^{\circ}$ in orthogonal coordinate. whereas rotated $180^{\circ}$, the error measured 0.9 mm, 0.2 mm, 0.3 mm in X, Y, Z respectively. In the rotating coordinates, the more increased the rotating unbalance, the more raised average ratio of setup errors. The resolution of CBCT images showed 2 level of difference in the table recommended. CBCT had a good agreement compared to each recommended values which is the mechanical safety, geometry accuracy and image quality. The rotating unbalance of gentry vary hardly in orthogonal coordinate. However, in rotating coordinate of gantry exceeded the ${\pm}1^{\circ}$ of recommended value. Therefore, when we do sophisticated radiation therapy six dimensional correction is needed.

키워드

참고문헌

  1. C. A. McBain, A. M. Henry, J.sykes, et al.: X-ray volumetric imaging in image-guided radiotherapy: The new standard in on-treatment imaging, International Journal of Radiation Oncology Biology Physics, 64(4), 625-634, 2006 https://doi.org/10.1016/j.ijrobp.2005.09.018
  2. J. Bedford and A. Warrington,: Commissioning of volumetric modulated arc therapy VMAT, International Journal of Radiation Oncology Biology Physics, 73(2), 537-545, 2009 https://doi.org/10.1016/j.ijrobp.2008.08.055
  3. Jean-Pierre Bissonnette,: A quality assurance program for image quality of cone-beam CT guidance in radiation therapy, International Journal of Radiation Oncology Biology Physics, 35(5), 1807-1815, 2008
  4. Letourneau D, Wong JW, Oldham M, et al.: Cone-beam CT guided radiation therapy: technical implementation., Radiation. Oncology, 75(3), 279-286, 2005 https://doi.org/10.1016/j.radonc.2005.03.001
  5. W.Du and S. Gao,; Measuring the wobble of radiation field centers during gantry rotation and collimator movement on a linear accelerator, Medical Physics, 38(8), . 4575-4578, 2011 https://doi.org/10.1118/1.3609098
  6. Pejman Rowshanfarzad,; Detection and correction for EPID and gantry sag during arc delivery using cine EPID imaging, Medical Physics, 39(2), 623-634, 2012 https://doi.org/10.1118/1.3673958
  7. I. Ali and S. Ahmad,; Evaluation of the effects of sagging shifts on isocenter accuracy and dimage quality of cone-beam CT from kV on-board imager, Journal Applied Clinical Medical Physics, 10(3), 180-194, 2009 https://doi.org/10.1120/jacmp.v10i3.2930
  8. F Edward Boas, Dominik Fleischmann,; CT artifacts : Causes and reduction techhiques, Imaging Medcine, 4(2), 229-240, 2012 https://doi.org/10.2217/iim.12.13
  9. Weihua Mao, Michael Speiser, Paul Medin et. al.; Initial application of a geometric QA tool for integrated MV and kV imaging systems on three image guided radiotherapy systems, International Journal of Radiation Oncology Biology Physics, 38(5), 2335-2341, 2011
  10. Jean-Pierre Bissonnette, Peter A. Balter and Lei Dong, et al.; Task Group 179; Quality assurance for image-guided radiation therapy utilizing CT-based technologies, International Journal of Radiation Oncology Biology Physics, 39(4), 1946-1963, 2012
  11. Jeorg Lehmann, Julian Perks, Shedon Semon, et al.; Commissioning experience with cone-beam computed tomography for image-guided radiation theraphy, Journsl Applied Clinical Medical Phys, 8(3), 21-36, 2007
  12. K. R. Muralidhar, P. Narayana, Rajneesh Kumar et al.; Commissioning and quality assurace of the X-ray volume Imageing system of an image- guided radiotherapy capable linear accelerator, Medical. Physics, 33(2), 72-77, 2008 https://doi.org/10.4103/0971-6203.41276
  13. E. E. Klein, J. Hanley, J. Bayouth, F.F. et al.; Task Group 142 report; Quality assurance of medical acceleratiors, International Journal of Radiation Oncology Biology Physics, 36(9), 4197-4212, 2009