ESTRO 2025 - Abstract Book

S3333

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

ESTRO 2025

Conclusion: ASRT offers a fast, innovative approach that substantially improves target coverage in lung tumors treated with MRI linac, especially for lesions with a PTV volume under 15 cc. This technique is a recommended option for ensuring target coverage while minimizing planning complexity.

Keywords: Skin adaptive, MRIgRT, Lung

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Mini-Oral Drift motion and position errors of mediastinal lymph nodes during DIBH radiotherapy of lung cancer Sara Shahzadeh 1 , Lone Hoffmann 2 , Mai Lykkegaard Ehmsen 1 , Marianne Knap 2 , Esben Worm 2 , Ditte Sloth Møller 2 , Per Rugaard Poulsen 1,2 1 Danish Centre for Particle Therapy, Aarhus University Hospital, Aarhus, Denmark. 2 Department of Oncology, Aarhus University Hospital, Aarhus, Denmark Purpose/Objective: Deep-inspiration breath-hold (DIBH) during radiotherapy can potentially reduce dose to the lungs and heart compared to treatment in free breathing. However, breath-hold variations during treatment may result in intra fractional geometric instability, potentially decreasing target coverage. Using intra-treatment fluoroscopic kV imaging we investigated the 3D intra-fraction drift motion and geometrical position errors of mediastinal lymph node (LN) targets during DIBH lung cancer treatments.

Material/Methods:

This study includes fifteen locally-advanced lung cancer patients treated on Clinac or TrueBeam linacs (Varian) with 5-8 field intensity modulated radiotherapy for primary tumors and involved mediastinal LNs. The LN targets were marked with implanted fiducial markers. The patients were set up using daily DIBH cone-beam CTs with soft tissue match on the primary tumor. Each field was delivered in less than 20s in a single DIBH guided by an external gating block with 2mm external gating window. For 7-11 fractions per patient, 5Hz fluoroscopic kV images were acquired