ESTRO 2024 - Abstract Book

S4165

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

ESTRO 2024

[3] N. Cornelius and T. Kanade. Adapting optical-flow to measure object motion in reflectance and X-ray image sequences. In Proc. of the ACM SIGGRAPH/SIGART interdisciplinary workshop on Motion: representation and perception, pages 145–153, New York, NY, USA, 1986. Elsevier North-Holland, Inc.

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Digital Poster

Daily adaptive MR-guided SBRT of ultra-central lung tumors (NCT05354596) – first dosimetric results

Susanne N. Bekke 1 , Susan BN Biancardo 1 , Kristian Boye 2 , Cécile Peucelle 2 , Anders S Bertelsen 3 , Lone Hoffmann 4,5 , Tine Schytte 3,6 , Mette Pøhl 2 , Gitte Persson 1,7 1 Copenhagen University Hospital - Herlev and Gentofte, Department of Oncology, Copenhagen, Denmark. 2 Copenhagen University Hospital - Rigshospitalet, Department of Oncology, Copenhagen, Denmark. 3 Odense University Hospital, Department of Oncology, Odense, Denmark. 4 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark. 5 Aarhus University, Department of Clinical Medicine, Aarhus, Denmark. 6 University of Southern Denmark, Institute of Clinical Research, Odense, Denmark. 7 Faculty of Health, University of Copenhagen, Department of Clinical Medicine, Copenhagen, Denmark

Purpose/Objective:

STAR-LUNG is a prospective multicenter phase II trial (NCT05354596), evaluating the safety and efficacy of stereotactic radiotherapy for ultra-centrally located lung tumors using daily adaptive MR-guided photon therapy. The primary endpoint is grade ≥ 4 treatment-related adverse events within 6 months after SBRT. We present the achieved target dose for the first 48 treatment fractions and evaluate the dosimetric effect of online daily adaptation.

Material/Methods:

From two centers seven patients (age 55-91 years) were enrolled. The fractionation scheme was 56 Gy in 8 fractions to the PTV (= GTV + 5mm margin) aiming at V 95% > 95%, using an inhomogeneous dose distribution with mean dose escalation to the GTV of up to 85 Gy and a max dose limited to 110 Gy. Constraints to organs at risk (OARs) were prioritized over target coverage. However, a minimum PTV coverage of D 99% > 26 Gy was required to ensure non inferiority to a palliative fractionation scheme. Patients were treated on a 0.35 Tesla MR-linac (MRidian, Viewray). An MR simulation was used to create a baseline plan that included the contours of aorta, main bronchi, lobar bronchi, esophagus, heart, trachea, lungs, spinal cord, and thoracic wall together with the GTV. Online, the OARs were re contoured within an adaptive ring around the PTV in a distance of 3 cm (2 cm craniocaudal). Connective tissue was defined as everything not delineated within the adaptive ring. At each treatment fraction, the baseline plan was calculated on the daily acquired MRI of the patient (predicted plan). From this point, further optimization could be done to create a new plan (adapted plan). Decision criteria to select whether to treat with the predicted or the adapted plan were the following: 1) no violation of OAR constraints should occur, 2) target coverage is improved. In some cases where the adapted plan was selected, keeping the OAR constraints thus came at the price of a decreased target dose compared to the predicted plan. The GTV mean dose and the PTV D 99% were extracted from the predicted plan and from the delivered plan.