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Investigation of the mechanical performance of Siemens linacs components during arc: gantry, MLC, and electronic portal imaging device

Authors Rowshanfarzad P, Häring P, Riis H, Zimmermann S, Ebert M

Received 2 June 2015

Accepted for publication 31 August 2015

Published 5 November 2015 Volume 2015:8 Pages 457—466


Checked for plagiarism Yes

Review by Single anonymous peer review

Peer reviewer comments 3

Editor who approved publication: Dr Scott Fraser

Pejman Rowshanfarzad,1 Peter Häring,2 Hans L Riis,3 Sune J Zimmermann,3 Martin A Ebert1,4

1School of Physics, The University of Western Australia, Crawley, WA, Australia; 2German Cancer Research Center (DKFZ), Medical Physics in Radiation Oncology, Heidelberg, Germany; 3Radiofysisk Laboratorium, Odense University Hospital, Odense C, Denmark; 4Department of Radiation Oncology, Sir Charles Gairdner Hospital, Nedlands, WA, Australia

Background: In radiotherapy treatments, it is crucial to monitor the performance of linac components including gantry, collimation system, and electronic portal imaging device (EPID) during arc deliveries. In this study, a simple EPID-based measurement method is suggested in conjunction with an algorithm to investigate the stability of these systems at various gantry angles with the aim of evaluating machine-related errors in treatments.
Methods: The EPID sag, gantry sag, changes in source-to-detector distance (SDD), EPID and collimator skewness, EPID tilt, and the sag in leaf bank assembly due to linac rotation were separately investigated by acquisition of 37 EPID images of a simple phantom with five ball bearings at various gantry angles. A fast and robust software package was developed for automated analysis of image data. Three Siemens linacs were investigated.
Results: The average EPID sag was within 1 mm for all tested linacs. Two machines showed >1 mm gantry sag. Changes in the SDD values were within 7.5 mm. EPID skewness and tilt values were <1° in all machines. The maximum sag in leaf bank assembly was <1 mm.
Conclusion: The method and software developed in this study provide a simple tool for effective investigation of the behavior of Siemens linac components with gantry rotation. Such a comprehensive study has been performed for the first time on Siemens machines.

Keywords: linac, Siemens, arc, sag, EPID, gantry

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