ESTRO 2025 - Abstract Book

S1373

Clinical - Lung

ESTRO 2025

2783

Proffered Paper Impact of Different Mediastinal Staging Modalities on Target Volume Delineation in LA-NSCLC: Secondary Analysis of the Randomized PET-Plan Trial Cas Stefaan Dejonckheere 1 , Andreas Rimner 2 , Jörg Sahlmann 3 , Simeon Ari Barth 4 , Tanja Schimek-Jasch 2 , Sonja Adebahr 2 , Markus Hecht 5 , Cornelius F. Waller 6 , Severin Schmid 7 , Matthias Miederer 8 , Alexander Brose 9 , Harald Binder 10 , Jochem König 11 , Anca-Ligia Grosu 2 , Ursula Nestle 2,12 , Eleni Gkika 2 1 Department of Radiation Oncology, University Hospital Bonn, Bonn, Germany. 2 Department of Radiation Oncology, University of Freiburg, Freiburg, Germany. 3 Institute of Medical Biometry and Statistics, University of Freiburg, Freiburg, Germany. 4 Department of Pediatrics, University of Freiburg, Freiburg, Germany. 5 Department of Radiotherapy and Radiation Oncology, Saarland University Medical Center, Homburg, Germany. 6 Department of Hematology, University of Freiburg, Freiburg, Germany. 7 Department of Thoracic Surgery, University of Freiburg, Freiburg, Germany. 8 Department of Translational Imaging in Oncology, University of Technology Dresden, Dresden, Germany. 9 Department of Diagnostic and Interventional Radiology, University Hospital Giessen, Giessen, Germany. 10 Institute of Medical Biometry and Statistics, University of Freiburg, Freiburg, Germany. 11 Institute of Medical Biostatistics, Epidemiology, and Informatics, University Hospital Mainz, Mainz, Germany. 12 Department of Radiation Oncology, Kliniken Maria Hilf, Mönchengladbach, Germany Purpose/Objective: To evaluate the role of different invasive and non-invasive mediastinal staging methods in patients with locally advanced non-small-cell lung cancer (NSCLC) treated with definitive chemoradiotherapy in the prospective PET-Plan trial (ARO-2009-09; NCT00697333) and to evaluate the impact of endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) and mediastinoscopy on target volume definition. Material/Methods: Patients treated per-protocol (n = 172), all receiving isotoxically dose-escalated chemoradiotherapy, were included in this unplanned secondary analysis. Radiation treatment planning was based on an 18F-FDG PET/CT targeting all CT positive lymph nodes (i.e. short axis diameter > 10 mm), even if PET-negative, plus elective nodal irradiation (arm A) or targeting only PET-positive nodes (arm B). The concordance rate between different staging modalities and their impact on target volume delineation were calculated. Results: The median follow-up time (95% confidence interval) was 41.1 (33.8−50.4) months. A total of 2,752 lymph node stations were evaluated non-invasively, 330 were examined invasively. Of 172 patients, 87 (50.6%) underwent at least one invasive staging modality. The number of different staging procedures per patient did not correlate with any of the primary endpoints (OS, PFS, or FFLP). The sensitivity of 18F-FDG PET/CT was 89.7% (78/87) and the specificity 67.5% (112/166) based on histology as assessed by EBUS. When using the results from mediastinoscopy, the sensitivity of PET was 82.6% (19/23) and the specificity 66.7% (36/54). Based on invasive staging methods, 13 lymph node stations in 9 patients (10.3%) were PET-negative while positive on invasive staging, thus leading to a significant adjustment of the target volume. Conclusion: In this unplanned secondary analysis of the XXX trial, the additional use of invasive staging resulted in relevant changes of the target volume in a tenth of patients. Invasive staging did not, however, have an effect on outcome in this trial, with a very low rate of isolated out-of-field recurrences (6 in arm A versus 3 in arm B). Radiation treatment planning can thus be based on invasive staging in addition to non-invasive PET in patients undergoing definitive chemoradiotherapy for locally advanced NSCLC. Prospective randomized data are required to confirm these findings.

Keywords: NSCLC, definitive chemoradiotherapy, staging