ESTRO 2025 - Abstract Book

S3208

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2025

670

Digital Poster Evaluating the impact of respiratory motion on airway dosimetry using deformable image registration in central and ultra-central lung SABR Evan Keane 1,2 , Gerard G Hanna 3,4 , Serena O'Keefe 2 , Maeve Keys 4 , Lorna Keenan 4 , Sinead Brennan 4 , John Armstrong 4 , Pierre Thirion 4,5 , Ciaran Malone 2 1 UCD School of Physics, University College Dublin, Dublin, Ireland. 2 Department of Physics, St. Luke's Radiation Oncology Network, Dublin, Ireland. 3 School of Medicine, Trinity College Dublin, Dublin, Ireland. 4 Department of Radiation Oncology, St. Luke's Radiation Oncology Network, Dublin, Ireland. 5 School of Medicine, Trinity St. James's Cancer Institute, Trinity College Dublin, Dublin, Ireland Purpose/Objective: Stereotactic ablative body radiotherapy (SABR) is a highly effective treatment for medically inoperable non-small cell lung cancer, offering excellent local tumour control. However, SABR for centrally located lung tumours poses significant risks, especially to nearby critical structures such as the central airways [1]. This project aimed to estimate the accuracy of the average value intensity projection (AvIP) for airway delineation and the suitability of a 5 mm planning risk volume (PRV). This study quantified the dosimetric impact of respiratory motion on the airways using 4-dimensional (4D) dose accumulation. Material/Methods: A retrospective study of 18 patients, 11 with ultra-central and 7 with central lung tumours, each treated with 60 Gy in 8 fractions was conducted. The clinically acquired 4DCT was used to image the anatomy throughout 10 phases of the respiratory cycle. Deformable image registration was used to propagate the central airway contours (trachea, main bronchi, bronchial tree) from the original plan, created on the AvIP, onto each phase of the 4DCT. The dose was calculated on each phase (shown in Figure 1 (B)) and accumulated back to a single dose distribution which was compared to the original AvIP plan. A schematic of this process is shown in Figure 1 (A).