Abstract
Portal imaging using electronic portal imaging device (EPID) is a well-established image-guided radiation therapy (IGRT) technique for external beam radiation therapy. The aims of this study are threefold; (i) to assess the accuracy of isocentre localization in the fiducial-based stereoscopic image registration, (ii) to investigate the impact of errors in the beam collimation device on stereoscopic registration, and (iii) to evaluate the intra- and inter-observer variability in stereoscopic registration. Portal images of a ball bearing phantom were acquired and stereoscopic image registrations were performed based on a point centred in the ball bearing as the surrogate for registration. Experiments were replicated by applying intentional offsets in the beam collimation device to simulate collimation errors. The accuracy of fiducial markers localization was performed by repeating the experiment using three spherical lead shots implanted in a pelvic phantom. Portal images of pelvis phantom were given to four expert users to assess the inter-observer variability in performing registration. The isocentre localization accuracy tested using ball bearing phantom was within 0.3 mm. Gravity-induced systematic errors of beam collimation device by 2 mm resulted in positioning offsets of the order of 2 mm opposing the simulated errors. Relatively large inter-portal pair projection errors ranges from 1.3 mm to 1.8 mm were observed with simulated errors in the beam collimation device. The intra-user and inter-user variabilities were observed to be 0.8 and 0.4 mm respectively. Fiducial-based stereoscopic image registration using EPID is robust for IGRT procedure.
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Acknowledgments
This study was carried out at Genesis Cancer Care WA (formerly Perth Radiation Oncology), Wembley, Western Australia. The authors thank the assistance of Sara Lyons Hackett and Simon Woodings in the preparation of this manuscript. They also acknowledge the financial support of one of the authors (N.M. Ung) by the Malaysian Ministry of Higher Education and the University of Malaya.
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Ung, N.M., Wee, L. On the accuracy of localization achievable in fiducial-based stereoscopic image registration system using an electronic portal imaging device. Australas Phys Eng Sci Med 35, 205–213 (2012). https://doi.org/10.1007/s13246-012-0148-y
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DOI: https://doi.org/10.1007/s13246-012-0148-y