ESTRO 2025 - Abstract Book

S3522

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTRO 2025

Material/Methods: Fourteen consecutive patients with recurrent or new non-small cell lung cancer treated with reirradiation type I or II [1] between 2013 and 2023 were included. Ten were treated with stereotactic radiotherapy and four with long course radiotherapy. The previous treatment dose was transferred to the new planning CT using deformable image registration followed by EQD2 rescaling with α/β=2 for spinal cord and α/β=3 otherwise. Two plans were created for each radiation modality in Eclipse v16.1; 66Gy/33 fractions, and 50Gy/24 fractions with dose escalation up to 66Gy in tumour and larger lymph nodes. The photon plans were IMRT plans with 5-7 fields and 5mm CTV-PTV margin (AcurosXB) and the proton plans were IMPT plans robustly optimised with 1-5 fields evaluated using 5mm setup error and 3.5% range uncertainty (AcurosPT). The reirradiation plans were initially evaluated with standard national Danish dose constraints for target and OAR. The cumulative dose in EQD2 was subsequently evaluated with the mandatory CURE Lung constraints (Table1). If these constraints were not met, target coverage was compromised iteratively. OAR doses for all plans were compared using a two-sided paired sample Wilcoxon signed-rank test.