Abstract
BackgroundIn modern radiotherapy, it is crucial to monitor the performance of all linac components including gantry, collimation system and electronic portal imaging device (EPID) during arc deliveries. In this study, a simple EPID-based measurement method has been introduced in conjunction with an algorithm to investigate the stability of these systems during arc treatments with the aim of ensuring the accuracy of linac mechanical performance.MethodsThe Varian EPID sag, gantry sag, changes in source-to-detector distance (SDD), EPID and collimator skewness, EPID tilt, and the sag in MLC carriages as a result of linac rotation were separately investigated by acquisition of EPID images of a simple phantom comprised of 5 ball-bearings during arc delivery. A fast and robust software package was developed for automated analysis of image data. Twelve Varian linacs of different models were investigated.ResultsThe average EPID sag was within 1 mm for all tested linacs. All machines showed less than 1 mm gantry sag. Changes in SDD values were within 1.7 mm except for three linacs of one centre which were within 9 mm. Values of EPID skewness and tilt were negligible in all tested linacs. The maximum sag in MLC leaf bank assemblies was around 1 mm. The EPID sag showed a considerable improvement in TrueBeam linacs.ConclusionThe methodology and software developed in this study provide a simple tool for effective investigation of the behaviour of linac components with gantry rotation. It is reproducible and accurate and can be easily performed as a routine test in clinics.
Highlights
In modern radiotherapy, it is crucial to monitor the performance of all linac components including gantry, collimation system and electronic portal imaging device (EPID) during arc deliveries
Where (EPID SagX)θ and (EPID SagY)θ are the EPID sag in X and Y directions at θ gantry angle; eθX and eθY are the positions of the centre of ball bearing (e) in X and Y directions at θ gantry angle; the terms (A cos θ) and (B sin θ) are applied to correct for the lateral and vertical displacements induced as a result of misalignments of lasers or displacement of ball bearing (e) from the isocentre
Each set of results for gantry rotation in CW direction and zero collimator angle is presented in graphs and every point is given as the average ±1SD
Summary
It is crucial to monitor the performance of all linac components including gantry, collimation system and electronic portal imaging device (EPID) during arc deliveries. Electronic portal imaging devices (EPIDs) have been widely used for patient positioning, quality assurance tests on linear accelerators, and pre- and post-treatment dosimetry verification [4,5,6,7]. They are routinely tested for geometric accuracy, image quality, and operational safety [8,9]. The arm has joints which are not quite rigid This could degrade image quality and affect the accuracy of EPID-based mechanical and dosimetric QA
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
