ESTRO 2024 - Abstract Book

S1727

Clinical - Lung

ESTRO 2024

Sebastian Regnery, Efthimios Katsigiannopulos, David Neugebauer, Fabian Weykamp, Philipp Hoegen, Tanja Eichkorn, Maximilian Deng, Carolin Buchele, Carolin Rippke, Sebastian Klüter, Laila König, Jürgen Debus, Juliane Hörner-Rieber

University Hospital Heidelberg, Department of Radiation Oncology, Heidelberg, Germany

Purpose/Objective:

Stereotactic body radiotherapy (SBRT) of ultracentral lung tumors close to the proximal bronchial tree (PBT) is effective but may cause severe bronchial bleedings [1, 2]. In the prospective MAGELLAN trial, we investigate stereotactic MR-guided online adaptive radiotherapy (SMART) as innovative technique to enable both effective and safe treatment of ultracentral lung tumors [3]. Our aim is to develop a backup strategy for SMART in case of an MR linac downtime based on the first patients’ data.

Material/Methods:

MAGELLAN is a phase I dose escalation trial. Patients with ultracental lung tumors (PTV contact with PBT or esophagus) receive SMART on four dose levels: 10 x 5.0, 5.5, 6.0 and 6.5 Gy [3]. Briefly, patients undergo a daily 3D MRI, which is registered to the baseline imaging to perform plan adaptation to the updated target volume and organ contours. Additionally, cineMRI enables gated dose delivery. In this work, we analyze interfractional changes in the first five patients to develop a conventional linac-based backup strategy. Our idea is to use 1) larger CTV-PTV margins and 2) a planning risk volume (PRV) concept for the PBT to compensate for missing online plan adaptation. Moreover, a surface-guidance system at our conventional linacs (Vision RT®) enables treatment in deep-inspiration breath hold. To establish reasonable PTV and PRV concepts, we propagate PTV and PBT contours from all daily MRIs to the baseline MRI and fuse them (PTV all , PBT all ) ( Figure 1 ).

Figure 1: Projection of all daily PBT contours (upper panel) and CTV contours (lower panel) on the baseline MRI.