ESTRO 2025 - Abstract Book

S3660

Physics - Quality assurance and auditing

ESTRO 2025

References: 1. Kooy, H.M., et al., A case study in proton pencil-beam scanning delivery. Int J Radiat Oncol Biol Phys , 2010. 76(2): p. 624-30. 2. Renner, T.R., et al. Preliminary results of a raster scanning beam delivery system. in Proceedings of the 1989 IEEE Particle Accelerator Conference 'Accelerator Science and Technology . 1989. 3. Kraan, A.C., et al., Impact of spot size variations on dose in scanned proton beam therapy. Phys Med , 2019. 57: p. 58-64. 4. Liu, C., et al., Impact of spot size and spacing on the quality of robustly optimized intensity modulated proton therapy plans for lung cancer. Int J Radiat Oncol Biol Phys , 2018. 101(2): p. 479-489.

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Mini-Oral A new, centralised approach to SEAFARER applied in auditing PSQA for head and neck plans Lauren May 1 , Jose Antonio Baeza-Ortega 1 , Mohammad Hussein 2 , Sarah Porter 3 , Alisha Moore 3 , Peter B Greer 4,1 , Catharine H Clark 2,5,6 , Joerg Lehmann 4,1,7 1 School of Information and Physical Sciences, University of Newcastle, Newcastle, Australia. 2 Metrology for Medical Physics Centre, National Physical Laboratory, Teddington, United Kingdom. 3 Radiation Therapy Quality Assurance, Trans Tasman Radiation Oncology Group (TROG Cancer Research), Newcastle, Australia. 4 Department of Radiation Oncology, Calvary Mater Hospital, Newcastle, Australia. 5 Department of Radiotherapy Physics, University College London Hospital, London, United Kingdom. 6 Department of Medical Physics and Bioengineering, University College London, London, United Kingdom. 7 Institute of Medical Physics, University of Sydney, Sydney, Australia Purpose/Objective: Radiotherapy plan quality is vital in achieving optimal patient outcomes. Patient specific quality assurance (PSQA) procedures are important to verify radiotherapy treatment plans are delivered accurately. Hence, there is a need for confidence in PSQA systems to detect delivery errors that would have clinically significant dosimetric impacts. Following on from the SEAFARER project for remote PSQA verification [1], a new centralised planning approach [2] was used with the aim of verifying PSQA systems for a head and neck radiotherapy treatment case for centres across Australia and New Zealand. Material/Methods: A head and neck treatment plan created using protocols established in a previous clinical trial [3] was used. RayStation’s Fallback planning module (RaySearch Laboratories, Stockholm, Sweden) was employed to create plans of similar quality and robustness for common linac models. Using Python scripting, eleven copies of these plans were created and modified to simulate delivery errors. DVH analysis was performed to assess the impact of errors on target coverage and organs at risk (OARs) dose. These centrally created plans were then distributed to participating centres who were asked to use their clinical PSQA methodologies to determine which were acceptable when compared back to the original unedited plan dose calculation. Results: Beam models used in 109 facilities in Australasia were registered for the study. Plans having a >5% increase in max dose to the brainstem and/or spinal cord, or a >5% reduction in target coverage were expected to fail PSQA (Figure 1). However, 58% of centres passed at least one of these plans using their clinical PSQA system. In total, 18% of plans with a >5% dose increase to OARs were passed, and 35% of plans with a >5% reduction in target coverage.