ESTRO 2025 - Abstract Book

S2905

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

ESTRO 2025

3896

Digital Poster EQOR – A Tool for EQDX-based Optimization for Re-Irradiation Klara Kefer, Madalyne Day, Riccardo Dal Bello, Matthias Guckenberger, Nicolaus Andratschke, Stephanie Tanadini Lang Radiation Oncology, University Hospital of Zürich, Zürich, Germany Purpose/Objective: Reirradiation poses a complex challenge in balancing cumulative radiation doses, requiring strategies to minimize toxicity while maintaining effective tumor control. This project presents and evaluates a base dose optimization workflow, meaning that the previous irradiated dose is taken into account for the current treatment, integrated within a clinical treatment planning system. Material/Methods: The workflow was implemented in the Eclipse treatment planning system (Siemens Healthineers) using an ESAPI script. It allows the conversion of previously delivered dose distributions to the new fractionation, which is then used as a base dose plan for optimizing the new treatment. An overview of the workflow steps involved is presented in Figure 2. The base dose plan approach was evaluated for four patients previously treated at our institute. Treatment plans were re-optimized, and compared to the clinically delivered plans in terms of dose to the planning target volume (PTV), and critical organs at risk (OARs). The cohort included two patients treated for head and neck cancers, one for brain cancer, and one for thoracic cancer. In these cases, there was no PTV compromise required for OARs overlapping with the PTV (to achieve cumulative dose constraints) Results: Four patient plans were successfully optimized using the base dose optimization method. The PTV coverage was similar for both methods, with the median dose difference for each case being less than 1%. The same was observed for the D95% of the PTV. These results are summarized in Figure 2 (above). Two OARs were evaluated for each re-optimized patient showing a superiority of the base dose plan in terms of OAR sparing. Specifically, the mean dose and the D0.1cc for each evaluated OAR were either lower or within the same range as those of the clinically delivered plan. The results are illustrated in Figure 2 (below).