ESTRO 2025 - Abstract Book

S2742

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

Results: The retrospective analysis revealed substantial variability in PSQA outcomes across centres, especially for HN plans, with significant differences between treatment sites observed at C1. Variations across optimizers were evident, though these may be influenced by specific details of the PSQA practices (Figure 1).

In contrast, plan complexity differences were more pronounced across optimizers and centers rather than across treatment sites. For instance, the Volo Ultra (VU) optimizer generated plans with lower Modulation Factor and smaller connected leaf apertures compared to Raystation (RS) and Volo (Figure 2).

Prospective data collection confirmed these trends, with only minor variations in plan complexity and PSQA outcomes across centres and optimizers. Despite all plans meeting clinical endpoints, PQM% values showed consistent variability (PQM%: C1-VOLO = 57.4±7.2%; C2-VOLO = 35.5±3.1%; C2-RS = 57.4±9.0%; C3-VU = 58.5±7.9%) Additionally, the three centers demonstrated different planning habits in balancing objectives for the target volume(s) and for organs at risk, with C1 achieving superior target coverage and homogeneity compared to C2 and C3. These findings suggest that planners' choices can impact clinical suitability and plan complexity characteristics as much as the optimizer, highlighting the need for standardized procedures and clear benchmarks. Conclusion: This study demonstrates that distinct Helical Tomotherapy optimizers yield different plan complexity characteristics. However, variability in PSQA outcomes and clinical suitability is driven primarily by planner habits and centre specific practices. These findings highlight a crucial need for standardised planning practices, particularly for less prevalent techniques, to improve consistency and predictability across centres. Promoting uniform planning protocols and clinical habits can substantially reduce variability, enabling more reliable and consistent treatment quality, ultimately benefiting patient outcome.

Keywords: Tomotherapy, Plan Complexity, Multicentric