Progress in Medical Physics (한국의학물리학회지:의학물리)

Korean Society of Medical Physics (한국의학물리학회)
권호 표지

Development of a Method to Measure the Radiation Isocenter Size of Linear Accelerators and Quantitative Analysis of the Radiation Isocenter Size for Clinac 21EX Linear Accelerator

선형가속기 방사선 중심점의 크기 측정 방법 개발과 Clinac 21EX 선형가속기의 방사선 중심점 크기 분석

  • Jeon, Ho-Sang (Department of Radiation Oncology, Pusan National University Yangsan Hospital) ;
  • Nam, Ji-Ho (Department of Radiation Oncology, Pusan National University Yangsan Hospital) ;
  • Park, Dahl (Department of Radiation Oncology, Pusan National University Hospital) ;
  • Kim, Yong-Ho (Department of Radiation Oncology, Pusan National University Hospital) ;
  • Kim, Won-Taek (Department of Radiation Oncology, Pusan National University School of Medicine) ;
  • Kim, Dong-Won (Department of Radiation Oncology, Pusan National University School of Medicine) ;
  • Ki, Yong-Kan (Department of Radiation Oncology, Pusan National University Hospital) ;
  • Kim, Dong-Hyun (Department of Radiation Oncology, Pusan National University Hospital)
  • 전호상 (양산부산대학교병원 방사선종양학과) ;
  • 남지호 (양산부산대학교병원 방사선종양학과) ;
  • 박달 (부산대학교병원 방사선종양학과) ;
  • 김용호 (부산대학교병원 방사선종양학과) ;
  • 김원택 (부산대학교 의학전문대학원 방사선종양학교실) ;
  • 김동원 (부산대학교 의학전문대학원 방사선종양학교실) ;
  • 기용간 (부산대학교병원 방사선종양학과) ;
  • 김동현 (부산대학교병원 방사선종양학과)
  • Received : 2011.07.13
  • Accepted : 2011.09.19
  • Published : 2011.09.30
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Abstract

A method to get a size of the radiation isocenter of linear accelerators using star-shot images was presented and a computer program was developed to automate the method. Accuracy of the method was verified. The developed program was used to measure sizes of the radiation isocenters for a Clinac 21EX (Varian, USA) using data of quality assurance (QA) performed from June 2008 to December 2010. To calculated the size of radiation isocenter, positions of two points on each central ray of the star-shot image were found and the equation of the central ray was determined using the positions of two points. Using the equations of central rays the radius of the minimum circle intersecting all the central rays, which is one half of the size of radiation isocenter, was calculated. The program measured x-intercepts and y-intercepts of the central rays within errors of 0.084 mm and sizes of radiation isocenters within 0.053 mm. All the errors were less than the spatial resolution of star-shot images 0.085 mm. The radiation isocenter sizes of Clinac 21EX were $0.33{\pm}0.27mm$, $0.71{\pm}0.36mm$, $0.50{\pm}0.16mm$ for collimator, gantry and couch respectively. During the measurement period all the measured sizes were less than 2.0 mm and within tolerance. The developed program could calculate the size of radiation isocenters and it would be helpful to routine QA.

Star-shot 영상을 이용한 선형가속기의 방사선중심점(radiation isocenter)에 대한 정도관리를 정량적으로 할 수 있는 방법을 개발하고 이를 컴퓨터 프로그램으로 구현하였다. 구현한 프로그램의 정확도를 검증하고 프로그램을 사용하여 2008년 6월부터 2010년 12월 사이에 수행한 선형가속기 Clinac 21EX (Varian, USA)의 방사선중심점의 정도관리 정보로부터 방사선중심점의 크기를 측정하여 어떤 변화가 있는지 분석하였다. 개발한 방법은 먼저 star-shot 영상의 빔(ray)들 각각의 중심선 위에 있는 두 개의 점들을 찾아서 모든 중심선들의 방정식을 구하고 구한 방정식을 이용하여 중심선들을 모두 가로지르는 원의 최소의 직경을 찾아 방사선중심점의 크기를 구하는 것이다. 프로그램은 중심선의 x-절편과 y-절편을 0.084 mm 이하의 정확도로 찾아냈고 방사선중심점의 크기는 0.053 mm의 정확도로 구하여 검증에 사용한 영상의 해상도 0.085 mm보다 작았다. Clinac 21EX의 radiation isocenter의 크기는 콜리메이터, 갠트리, 테이블 각각 $0.33{\pm}0.27mm$, $0.71{\pm}0.36mm$, $0.50{\pm}0.16mm$였고 측정 기간 동안 2.0 mm보다 작게 나와 모두 허용한도를 만족하였다. 개발한 프로그램은 충분한 정확도로 방사선중심점의 크기를 계산해주어 정기적인 정도관리에 많은 도움이 될 것으로 생각된다.

Keywords

References

  1. Nath R, Biggs PJ, Bova FJ, et al: AAPM code of practice for radiotherapy accelerators: Report of AAPM Radiation Therapy Task Group No. 45. Med Phys 21:1093-1121 (1994) https://doi.org/10.1118/1.597398
  2. Lutz W, Winston KR, Maleki N: A system for stereotactic radiosurgery with a linear accelerator. Int J Radiat Oncol Biol Phys 14:373-381 (1988) https://doi.org/10.1016/0360-3016(88)90446-4
  3. Dong L, Shiu A, Tung S, Boyer A: Verification of radiosurgery target point alignment with an electronic portal imaging device (EPID). Med Phys 24:263-267 (1997) https://doi.org/10.1118/1.598070
  4. Galvin JM, G. Bednarz: Quality assurance procedures for stereotactic body radiation therapy. Int J Radiat Oncol Biol Phys 71:S122-S125 (2008) https://doi.org/10.1016/j.ijrobp.2007.10.002
  5. Low DA, Li Z, Drzymala RE: Minimization of target positioning error in accelerator-based radiosurgery. Med Phys 22:443- 448 (1995) https://doi.org/10.1118/1.597475
  6. Serago FC, Lewin AA, Houdek PV, et al: Radiosurgery target point alignment errors detected with portal film verification. Int J Radiat Oncol Biol Phys 24:777-780 (1992) https://doi.org/10.1016/0360-3016(92)90728-Z
  7. Tsai JS: Analyzes of multi-irradiation film for system alignments in stereotactic radiotherapy (SRT) and radiosurgery (SRS). Phys Med Biol 41:1597-1620 (1996) https://doi.org/10.1088/0031-9155/41/9/003
  8. Winey B, Sharp G, Bussière M: A fast double template convolution isocenter evaluation algorithm with subpixel accuracy. Med Phys 38:223-227 (2011) https://doi.org/10.1118/1.3524227
  9. Rowshanfarzad P, Sabet M, O' Connor DJ, Greer PB: Verification of the linac isocenter for stereotactic radiosurgery using cine-EPID imaging and arc delivery. Med Phys 38:3963- 3970 (2011) https://doi.org/10.1118/1.3597836
  10. Kutcher GJ, Coia L, Gillin M, et al: Comprehensive QA for radiation oncology: Report of AAPM Radiation Therapy Committee Task Group 40. Med Phys 21:581-618 (1994)
  11. Klein EE, Hanley J, Bayouth J, et al: Task Group 142 report: Quality assurance of medical accelerators. Med Phys 36: 4197-4212 (2009) https://doi.org/10.1118/1.3190392
  12. Hudson FR: A simple isocenter checking procedure for radiotherapy treatment machines using the optical pointer. Med Phys 15:72-73 (1988) https://doi.org/10.1118/1.596159
  13. Woo MK: A personal-computer-based method to obtain "starshots" of mechanical and optical isocenters for gantry rotation of linear accelerators. Med Phys 29:2753-2755 (2002) https://doi.org/10.1118/1.1521937
  14. Gibbs FA, Buechler D, Leavitt DD, Moeller JH: Measurement of mechanical accuracy of isocenter in conventional linear-accelerator-based radiosurgery. Int J Radiat Oncol Biol Phys 25:117-122 (1992)
  15. Tsai JS, Curran BH, Sternick ES, Engler MJ: The measurement of linear accelerator isocenter motion using a three-micrometer device and an adjustable pointer. Int J Radiat Oncol Biol Phys 34:189-195 (1996) https://doi.org/10.1016/0360-3016(95)02085-3
  16. Riis HL, Zimmermann SJ, Riis P: Isocentric rotational performance of the Elekta Precise Table studied using a USBmicroscope. Phys Med Biol 55:7597-7614 (2010) https://doi.org/10.1088/0031-9155/55/24/014
  17. Skworcow P, Mills JA, Haas OCL, Burnham KJ: A new approach to quantify the mechanical and radiation isocentres of radiotherapy treatment machine gantries. Phys Med Biol 52: 7109-7124 (2007) https://doi.org/10.1088/0031-9155/52/23/022
  18. Arjomandy B, Altschuler MD: A quality assurance device for the accuracy of the isocentres of teletherapy and simulation machines. Phys Med Biol 45:2207-2217 (2000) https://doi.org/10.1088/0031-9155/45/8/310
  19. González A, Castro I, Martínez JA: A procedure to determine the radiation isocenter size in a linear accelerator. Med Phys 31:1489-1493 (2004) https://doi.org/10.1118/1.1755491
  20. Rosca F, Lorenz F, Hacker FL, Chin LM, Ramakrishna N, Zygmanski P: An MLC-based linac QA procedure for the characterization of radiation isocenter and room lasers' position. Med Phys 33:1780-1787 (2006) https://doi.org/10.1118/1.2198171
  21. Du W, Yang JA: A Robust Hough transform algorithm for determining the radiation centers of circular and rectangular fields with subpixel accuracy. Phys Med Biol 54:555-567 (2009) https://doi.org/10.1088/0031-9155/54/3/006
  22. 이레나, 이수진, 최진호: 유럽, 미국, 일본의 선형가속기 정도관 리 비교. 의학물리 14:20-27 (2003)
  23. Gonzalez RC, Woods RE, Eddins SL: Ch.9 Morphological Image Processing. Digital Image Processing using MATLAB. Prentice-Hall, Upper Saddle River, NJ (2003), pp. 364-408