S2337
Physics - Quality assurance and auditing
ESTRO 2026
3289–3298. Keywords: SGRT, surface-guidance, gating latencies,
frame-rate camera (120 FPS) (GoPro Hero10, GoPro Inc., USA) [1]. A second camera (iPhone7, Apple Inc., USA) monitored an LED at the linac-gating system interface (Fig. 1); the LED indicates the gating system's beam-release/hold status. By filming a digital stopwatch, we assessed the cameras’ frame rates and synchronized the videos during post-processing. From the video frames, surface position, gating window information, beam, and LED state were extracted. Due to the signal transduction of the treatment unit, the temporal delay between the surface entry/exit of the gating window and the LED response (on/off) provided an upper-limit estimate of the gating system’s latency contribution. Latencies were measured for each duty cycle, at a Versa HD linac (Elekta AB, Sweden) with ExacTrac Dynamic (ETD) (Brainlab AG, Germany) and Synergy linac (Elekta AB) with Catalyst HD+ (C-Rad AB, Sweden).
Digital Poster 1125 Development of a National Guidance Document for Radiotherapy Quality Assurance in Investigator-Initiated Clinical Trials Sandra Harkin 1,2 , James Waldron 1,2 , Roisin OMaolalai 3 , Sinead Brennan 4,5 1 Physics, St. Lukes Radiation Oncology Network, Dublin, Ireland. 2 Physics, Irish Research in Radiation Oncology Group, Dublin, Ireland. 3 Radiation Therapy, Irish Research in Radiation Oncology Group, Dublin, Ireland. 4 Radiation Oncology, St. Lukes Radiation Oncology Network, Dublin, Ireland. 5 Radiation Oncology, Irish Research in Radiation Oncology Group, Dublin, Ireland Purpose/Objective: The Irish Radiation Research Oncology Group (IRROG) was established in 2022 with the aim of enhancing equitable access to radiotherapy (RT) clinical trials across the island of Ireland. A key objective of IRROG is to offer centralised expertise, coordination, and oversight, ensuring consistency and harmonisation of radiotherapy quality assurance (RTQA) across all
participating centres. Material/Methods:
To support this goal, a national guidance document has been developed, focusing on the establishment of RTQA programmes for investigator-initiated clinical trials in radiotherapy. This document places particular emphasis on defining the role of the medical physicist in this process. Results: The guidance document outlines the responsibilities of medical physicists involved in clinical trials, across IRROG-affiliated and other medical physics roles.In addition to identifying areas where physicist input would enhance the quality and integrity of radiotherapy trials, it also specifies domains where involvement is mandated by legislation. These responsibilities are categorised into six key domains (see Figure 1(a)).The document also offers practical recommendations for key RTQA processes, which have been divided into 4 main categories (see Figure 1(b)).
Results: Over five experimental days, ETD showed median beam-on and beam-off latencies of 106 (IQR 86-133) ms and 126 (104-152) ms. The overall latencies were 1326 (1009-1652) ms and 133 (115-156) ms. At Catalyst HD+ (cMotion disabled, one experimental day), beam- on and beam-off latencies were 146 (119-168) ms and 141 (120,167) ms, and overall latencies were 1263 (1215-1288) ms and 139 (122,174 ) ms.
Conclusion: With our portable method, we quantified the latencies of two linacs and their gating systems at a high time resolution. It enables consistent QA and comparative evaluation for any system with a light signal at the linac-gating system interface, providing a practical tool for assessing gating performance in SGRT. References: [1] Worm, E. S. et al. (2023). Medical Physics, 50(6),
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