ESTRO 2025 - Abstract Book

S3257

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

ESTRO 2025

Conclusion: The VitalHold module on the Radixact platform demonstrates strong potential for automated DIBH treatment, providing precise and reliable beam control under simulated breath-hold conditions, particularly for gating tolerances of 2 to 5 mm. This study supports the integration of automated breath-hold techniques in clinical practice.

Keywords: DIBH, Radixact, VitalHold

2434

Proffered Paper Automated target misalignment correction for CBCT-based online adaptive radiotherapy of locoregional lung cancer patients Carmen Seller Oria, Suzan Gerrets - van Noord, Sanne van Weerdenburg, Paula Bos, Suzanne van Beek, Marloes Frantzen-Steneker, Zeno Gouw, Jan Jakob Sonke, Peter Remeijer Department of Radiation Oncology, The Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital, Amsterdam, Netherlands Purpose/Objective: Locoregional lung cancer patients are treated at our institution with cone beam CT image guided radiotherapy (CBCT-IGRT). The primary tumor (GTVprim) and mediastinal lymph nodes regions, which move independently, are irradiated using one isocenter. Differential motion between mediastinal targets and GTVprim results in enlarged treatment margins for GTVprim, given that the treatment couch shift is performed according to the position of the carina 1 (in the mediastinum). An online adaptive RT (OART) workflow that automatically corrects for interfractional target misalignments has potential to reduce the PTV margin of GTVprim. In this work, a correction method for target misalignments is proposed for lung treatments to enable OART with smaller PTV margins. Material/Methods: With respect to IGRT, the proposed OART workflow introduces three additional steps after patient alignment: synthetic CT generation, plan re-optimization, and verification CBCT. Lung synthetic CTs were generated with “Smart Adapt” (SA), an in-house built module whose feasibility was proven in a prospective trial for prostate patients 2 . SA rigidly shifts the targets in the planning CT and its accompanying delineations to display them in the correct position. It creates a deformation vector field (DVF) by using local in-room registrations of the carina (table shift) and GTVprim, performed with XVI 3 . The DVF is subsequently applied to the planning CT and corresponding delineations to translate/rotate the relevant regions and produce the synthetic CT. In this way, the synthetic CT mitigates the residual GTVprim misalignment observed in the planning CT after table shift (figure 1a).