ESTRO 2025 - Abstract Book

S2743

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

ESTRO 2025

References: [1] Cavinato, S. et al. (2024). A software tool to extract complexity metrics from radiotherapy treatment plans. Medical Physics. [2] Fusella, M. et. al. (2021). Analysis of clinical patient-specific pre-treatment quality assurance with the new helical tomotherapy platform, following the AAPM TG-218 report. Radiation Oncology, 16, 1-7. [3] Cavinato, S. et al. (2023). Prediction models as decision-support tools for virtual patient-specific quality assurance of helical tomotherapy plans. Physics and Imaging in Radiation Oncology, 26, 100435.

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Digital Poster Plan evaluation of four lattice SBRT layouts using existing and novel dosimetry metrics Vanya Staykova 1 , David J Eaton 1 , Sarah Misson 1 , Mike Kirby 2,3

1 Medical Physics and Clinical Engineering Department, Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom. 2 Faculty of Biology, Medicine and Health, University of Manchester, Manchester, United Kingdom. 3 School of Allied Health Professions and Nursing, University of Liverpool, Liverpool, United Kingdom Purpose/Objective: Lattice radiotherapy (LRT) with regular geometric lattice layouts, has gained clinical and research attention due to better compatibility with automation in lattice creation and inverse planning [2, 3]. No definitive conclusions regarding optimum evaluation metrics, distribution pattern, and lattice geometries in LRT have been established, warranting further studies. This in silico study aims to evaluate heterogenous dose distributions in Lattice SBRT, using four different geometric lattice layouts applied to the same GTV across a patient cohort. Material/Methods: Four geometric lattice layouts with vertices’ diameter of 0.7, 1.0, 1.5, and 2.0cm (Table 1) have been investigated for large GTVs (867-1984cc) across five cases of various types tumours, following the planning and evaluation methodology of the LITE SABR M1 trial [2,4]. The prescribed doses were 66.70Gy to the high dose peaks-vertices (PTV_6670) and 20Gy to the rest of the GTV/PTV, in 5 fractions. Treatments plans were created with VARIAN Eclipse v15.6, HDMLC, RapidArc and Acuros-Dmed calculation algorithm, using 4 - 5 full or partial arcs. Results: The LRT plan evaluation metrics, as defined in previous studies [1-3], are presented in Table 1. The PTV_6670 median volume varies between 6.3 cc and 37.6 cc and ~1%-5% of the GTV, across the four layouts. The median of the mean doses of PTV_6670 and PTV_Avoid (the valley dose structures) and their ratio, DR, were similar across all four lattice layouts. The Peak-to-Valley-Dose-Ratio, PVDR= Dp/Dmean(100-95)% metric [1] showed a larger spread across the lattice layouts and the GTV volumes (Figure 1A).