ESTRO 2023 - Abstract Book

S224

Saturday 13 May

ESTRO 2023

Conclusion Database restrictions on LET had a greater effect on the fitting outcome than restrictions on ( α ⁄ β )_x. SOBP data predicted steeper increase in RBE with increasing LET compared to M data. Refitting published RBE models to all available data had a relatively large impact on model estimates, indicating that the models might not generalize well when applied to data outside the databases used to develop them. For low ( α ⁄ β )_x, where RBE variations are large, refits gave overall less RBE variations across the SOBP, especially in the distal part. OC-0289 Practical and effective ART alternatives in H&N IMPT approaching daily in-room replanning quality M. Oud 1,2 , S. Breedveld 1 , M. Gí ż y ń ska 2 , S. Habraken 1,2 , Z. Perkó 3 , B. Heijmen 1 , M. Hoogeman 1,2 1 Erasmus MC Cancer Institute, University Medical Center Rotterdam, Department of Radiotherapy, Rotterdam, The Netherlands; 2 HollandPTC, Department of Medical Physics & Informatics, Delft, The Netherlands; 3 Delft University of Technology, Department of Radiation Science and Technology, Delft, The Netherlands Purpose or Objective While daily online replanning (DailyPlan) may be considered the ultimate dosimetric solution to account for inter-fraction anatomical changes and patient setup errors in IMPT, issues with computation speed and online QA hinder clinical implementation. Therefore, robust planning combined with ad-hoc offline replanning (ClinAdapt) is currently used in clinical practice. The aim of this simulation study was to dosimetrically compare DailyPlan and ClinAdapt to three practical alternative ART strategies in head-and-neck (H&N) IMPT, weekly offline replanning (wOffR) and two strategies with daily plan selection from offline generated patient-specific plan libraries (PL1 & PL2). Materials and Methods 15 H&N IMPT patients with 3-6 repeat CTs (rCT) were included.