ESTRO 2025 - Abstract Book

S3662

Physics - Quality assurance and auditing

ESTRO 2025

Conclusion: Current clinical PSQA methods may miss clinically significant delivery errors. The SEAFARER centralised methodology supports identifying areas of PSQA which require attention and informing future protocol, hence, improving radiotherapy treatment delivery quality and safety.

Keywords: PSQA, remote auditing, sensitivity and specificity

References: [1] Lehmann, J., Hussein, M., Barry, M. A., Siva, S., Moore, A., Chu, M., ... & Clark, C. H. (2022). SEAFARER – A new concept for validating radiotherapy patient specific QA for clinical trials and clinical practice. Radiotherapy and Oncology, 171, 121-128. [2] Baeza-Ortega JA, Hussein, M., Greer PB, Clark CH, Lehmann J, Methodology for PSQA assessment with centrally created treatment plans using SEAFARER, AAPM Annual Meeting 2024 [3] Tyler J, Bernstein D, Seithel M, Rooney K, Petkar I, Miles E, Clark CH, Hall E, Nutting C. Quality assurance of dysphagia-optimised intensity modulated radiotherapy treatment planning for head and neck cancer. Physics and Imaging in Radiation Oncology. 2021 Oct 1;20:46-50.

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Digital Poster Comparison of radiation isocenter accuracy in Varian LINAC models using Winston-Lutz tests. Llorenç Benaches-Magraner, Ignasi Modolell-Farre, Manuel Cruz-González, Francisco Camba, Cristina Picón-Olmos Medical Physics and Radiological Protection Deparment, Hospital Duran i Reynals, L'Hospitalet de Llobregat, Spain Purpose/Objective: The aim of this study is to compare the results of Winston-Lutz tests evaluating gantry and collimator rotation across different LINAC models: Varian TrueBeam, Ethos and Halcyon systems. Material/Methods: Materials : Six linear accelerators were studied: two Halcyon ("Halcyon 11, Halcyon 12"), one Ethos system, one TrueBeam STx and two TrueBeams ("Truebeam 3320, TrueBeam 5229").

The BRAINLAB Frameless SRS QA Target Pointer was employed for the tests. Methods :

Winston-Lutz tests were performed for gantry and collimator rotation for all LINACs. For gantry rotation, Winston Lutz included 13 measurements at 30º intervals, spanning from 179.9º to 180.1º. For collimator rotation, TrueBeam LINACs were tested with 13 measurements every 30º, from 175º to 185º. Halcyon systems underwent 7 measurements, from 90º to 270º. The experiment was repeated different days.

The measurement setup for TrueBeam LINACs utilized a 6 MV 4x4 MLC field (jaws set to 5×5 cm). Ethos and Halcyon systems employed a 6FFF 4×4 cm field.

Data analysis was based in the Python library Pylinac (4).

Results: The following figures depict the results of the Winston-Lutz test for gantry (Figure 1) and collimator rotation (Figure 2).