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Original Article

Korean Journal of Medical Physics 2015; 26(4): 193-200

Published online December 30, 2015

Copyright © Korean Society of Medical Physics.

Commissioning Experience of Tri-Cobalt-60 MRI-guided Radiation Therapy System

Jong Min Park*†‡§, So-Yeon Park*†‡║, Hong-Gyun Wu*†‡¶, Jung-in Kim*†‡§

*Department of Radiation Oncology, Seoul National University Hospital, Seoul, Biomedical Research Institute, Seoul National University Hospital, Seoul, Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, §Center for Convergence Research on Robotics, Advanced Institutes of Convergence Technology, Suwon, Interdisciplinary Program in Radiation Applied Life Science, Seoul National University College of Medicine, Seoul, Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea

Received: November 23, 2015; Revised: December 1, 2015; Accepted: December 3, 2015

Abstract

The aim of this study is to present commissioning results of the ViewRay system. We verified safety functions of the ViewRay system. For imaging system, we acquired signal to noise ratio (SNR) and image uniformity. In addition, we checked spatial integrity of the image. Couch movement accuracy and coincidence of isocenters (radiation therapy system, imaging system and virtual isocneter) was verified. Accuracy of MLC positioing was checked. We performed reference dosimetry according to American Association of Physicists in Medicine (AAPM) Task Group 51 (TG-51) in water phantom for head 1 and 3. The deviations between measurements and calculation of percent depth dose (PDD) and output factor were evaluated. Finally, we performed gamma evaluations with a total of 8 IMRT plans as an end-to-end (E2E) test of the system. Every safety system of ViewRay operated properly. The values of SNR and Uniformity met the tolerance level. Every point within 10 cm and 17.5 cm radii about the isocenter showed deviations less than 1 mm and 2 mm, respectively. The average couch movement errors in transverse (x), longitudinal (y) and vertical (z) directions were 0.2 mm, 0.1 mm and 0.2 mm, respectively. The deviations between radiation isocenter and virtual isocenter in x, y and z directions were 0 mm, 0 mm and 0.3 mm, respectively. Those between virtual isocenter and imaging isocenter were 0.6 mm, 0.5 mm and 0.2 mm, respectively. The average MLC positioning errors were less than 0.6 mm. The deviations of output, PDDs between mesured vs. BJR supplement 25, PDDs between measured and calculated and output factors of each head were less than 0.5%, 1%, 1% and 2%, respectively. For E2E test, average gamma passing rate with 3%/3 mm criterion was 99.9%±0.1%.

KeywordsMRI-guided radiation therapy system, Commissioning, Co-60, Intensity modulated radiation therapy

Korean Society of Medical Physics

Vol.35 No.1
March 2024

pISSN 2508-4445
eISSN 2508-4453
Formerly ISSN 1226-5829

Frequency: Quarterly

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