S2338
Physics - Quality assurance and auditing
ESTRO 2026
2 Department of Radiation Oncology, University Hospitals UZ Leuven, Leuven, Belgium. 3 Department of Imaging & pathology; section Medical Physics & Quality Assessment, KU Leuven, Leuven, Belgium Purpose/Objective: Measurement-based patient-specific QAs are often impractical in adaptive workflows. Complexity metrics present a promising alternative and may also reduce QA workload in standard workflows. Current literature typically calculates these metrics at the plan-level1. However, intra-plan analysis could be feasible because of the consistent beam configuration used in class solutions (NCS 352). This potentially allows for tighter and more targeted QA thresholds. This was statistically investigated for beams from five clinical class solutions. Material/Methods: A retrospective analysis was performed on both clinical plans and plans used for class solution- commissioning for the following indications (Table 1): Breast/Thoracic Wall with SIB: 1 arc RapidArc Dynamic (RAD) + 1 arc VMAT, 15x2.67Gy/3.2GyBreast/Thoracic Wall with Nodes and SIB: 6 IMRT fields + 1 arc VMAT, 15x2.67Gy/3.2GyOligometastatic SBRT: 2 arcs VMAT, 3x10Gy (alternatively 3x9/8/7Gy or 5x6Gy)Palliative: 2 arcs VMAT, 5x4GyProstate SBRT: 2 arcs VMAT, 5x7GyFour complexity metrics were calculated per beam following Crijns et al.3: the number of MU per dose per fraction (MU/dose/fx), the leaf sequence variability4 (LSV), the aperture area variability4 (AAV), and the equivalent square field size (EqFS).Complexity differences between beams within a plan were tested using PERMANOVA with plan as strata, and PERMDISP (Euclidean distance, 9999 permutations, α =0.05). All metrics were standardized (z-score) prior to multivariate analysis. Results: Individual beams of treatment plans within the same class solution have significantly different complexity for four of the five class solutions (PERMANOVA p<0.05; Table 1, Figure 1). The strongest effects were found for Br/TW+SIB (R ² =0.48) and Br/TW+N+SIB (R ² =0.35), reflecting large complexity variations between IMRT, VMAT, and RAD beams. Only the palliative CCW-coll10°/CW-coll80° case showed no significant beam-level difference (p=0.29).In prostate SBRT, a significant difference was detected (pseudo- F=6.28, R ² =0.10, p=0.0006), however, PERMDISP revealed unequal dispersion between beam groups, suggesting that (part of) this effect was related to heterogeneity in variability. Dispersion was homogeneous in all other class solutions (PERMDISP p>0.05), confirming that observed effects primarily reflected true differences in beam-level complexity rather than spread.
Figure 1(a) The 6 areas of responsibility of medical physicists in radiotherapy clinical trials, as outlined in the IRROG National Guidance Document an (b) The four main categories of the RTQA programme included in the IRROG National Guidance Document with specific recommendations.Guidance is provided for both pre-trial and on-trial RTQA procedures, drawing on the collective experience of the IRROG team.In addition, the document includes:A comprehensive list of required documentation for RTQA programmesStandardised terminology for protocol deviations
Figure 2. Overview of the IRROG National Guidance Document Conclusion: This national guidance document is a requisite to support the standardisation and harmonisation of RTQA practices in investigator-initiated clinical trials. By consolidating the experience and expertise of IRROG professionals, it aims to facilitate the collection of high-quality data and improve consistency across trials conducted in Ireland. References: 1) The role of medical physics experts in clinical trials: A guideline from the European Federation of Organisations for Medical Physics, Abbot et al., Physica Medica 125 (2024) 104821 2) Guidance for the Physics Aspects of Clinical Trials, The Report of AAPM Task Group 113 4) Guideline for good clinical practice E6(R3), International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use, Jan 20255) Evaluation Definitions, Global Harmonisation Group (2013).
https://rtqaharmonization.org/resources Keywords: Clinical Trials, Radiotherapy
Digital Poster 1126 Complexity analysis should be performed at the beam-level Emma Van Riet 1 , Willemijn Goossens 2 , Wouter Michiels 3 , Robin De Roover 2 , Wouter Crijns 1,2 1 Laboratory of Experimental Radiotherapy, Department of Oncology, KU Leuven, Leuven, Belgium.
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