ESTRO 2025 - Abstract Book

S1334

Clinical - Lung

ESTRO 2025

registration. To generate a BH CTV, the 50% exhalation phase and the BH CT were deformably registered. The FB CTV was copied to the BH CT, adapted to anatomy and checked for consistency and comparable volume. For each patient, two IMPT plans were made: one on an average, FB 4D-CT, and one on the BH scan. The same beam setup was used. All plans were optimized to a prescription dose of 45 GyRBE in 25 fractions of 1.8 GyRBE (1.1 GyRBE = 1 Gy physical dose). Plans were robustly optimized with 5 mm setup and 3% range uncertainty and were evaluated on a voxelwise maximum and minimum dose distribution. A dosimetric comparison between the plans was made, focusing on mean dose to the heart (MHD), lungs (MLD) and esophagus (MED). Results: An example of a dose distribution for a FB and a BH plan is depicted in Figure 1. The effect of BH on OAR dose varied across patients. 1/10 of the patients showed a MHD reduction > 1 GyRBE and 1/10 of the patients had a MED reduction > 1 GyRBE. In 3/10 of the patients, the dose to one or more OARs increased by >0.5 GyRBE. While individual dose reductions up to -0.8 GyRBE (MLD), -1.3 GyRBE (MHD), and -2.0 Gy (MED) were observed, overall, all differences with the clinical plan were non-significant (Figure 2). The dose differences were -0.1±0.5 GyRBE (MLD, mean ± standard deviation), -0.1±0.7 GyRBE (MHD), -0.3±0.7 GyRBE (MED).