S841
Clinical - Lung
ESTRO 2026
NSCLC patients receiving concomitant immunochemotherapy. Material/Methods: Synchronous oligometastatic NSCLC patients treated with metastasis-directed SBRT and concurrent induction immunochemotherapy, followed by local treatment to the primary tumour, were included. FDG/PET-CT was performed at baseline, at 3 months post-induction (restaging), and at 1 year; CT imaging at 6 and 9 months. Quantitative analyses assessed changes in size (maximal diameter), volume, and SUVmax of bone and lung metastases. Qualitative evaluation addressed radiological response patterns in lung lesions, categorized as acute ( ≤ 6 months, Palma et al.) or late (>6 months, Dahele et al.) changes. Results: SBRT was delivered to 25 bone and 20 lung metastases, with 37.5–58 Gy in 3–10 fractions.Median (IQR) normalized changes in bone metastases (baseline vs restaging) were: size 0.84 ([0.46-0.85], 16% decreased), volume 0.69 ([0.46-0.85], 31.3% decreased), and SUVmax 0.37 ([0.30-0.54], 63% decreased, 2 lesions increased). This early imaging response persisted at 12 months. One bone metastasis progressed at 6 months, another enlarged but remained metabolically inactive at 12 months, achieving 95% 12-month freedom from local progression (FFLP) (Figure 1A). Median (IQR) changes in lung metastases were (baseline vs restaging): size 0.87 ([0.64-1.27], 13.4% decreased), volume 0.38 ([0.17-1.51], 62% decreased), and SUVmax 0.45 ([0.19- 0.55], 55% decreased, 2 lesions increased). At 12 months, SUVmax decline persisted, with more variable size and volume. One lung metastasis showed isolated metabolic increase at 12 months, deemed radiologically non-progressive, achieving 100% 12- month FFLP (Figure 1B). Qualitative analysis at 3 months showed no increased density in most lung metastases (14/20, 70%), with one diffuse consolidation (5%); at 9 and 12 months, most showed a modified conventional pattern (71% and 54.5%) (Figure 2). Six metastases changed categories across timepoints, 4 in the acute and 2 in the late phase. The morphological response pattern showed no atypical or novel CT changes up to 12 months, without increased inflammatory or fibrotic changes after SBRT.
Digital Poster Highlight 4352 Longitudinal imaging analysis of bone and lung oligometastases after SBRT and immunochemotherapy: a secondary analysis of the ETOP CHESS trial Nicolas Martz 1,2 , Alina Paunoiu 1 , Frank Van den Heuvel 1 , Isabelle Opitz 3 , Rolf Stahel 4 , Alessandra Curioni-Fontecedro 5 , Ferdinando Cerciello 6 , Ivana Sullivan 7 , Lizza Hendriks 8 , Miriam Dorta 9 , Ana Callejo 10 , Alfredo Addeo 11 , Anne-Marie Dingemans 12 , Giulia Pasello 13 , Anne-Christine Piguet 4 , Susanne Roux 4 , Urania Dafni 14 , Solange Peters 15 , Martin Hüllner 16 , Thomas Frauenfelder 17 , Stephanie Tanadini-Lang 1 , Matthias Guckenberger 1 1 Department of Radiation Oncology, University Hospital Zürich, Zürich, Switzerland. 2 Department of Radiation Oncology, Institut de Cancérologie de Lorraine, Nancy, France. 3 Department of Thoracic surgery, University Hospital Zürich, Zürich, Switzerland. 4 Coordinating Center, ETOP IBCSG Partners Foundation, Bern, Switzerland. 5 Department of Medical Oncology, Hôpital Cantonal HFR Fribourg, Fribourg, Switzerland. 6 Department of Medical Oncology, Bern University Hospital, Bern, Switzerland. 7 Department of Medical Oncology, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain. 8 Department of Pulmonary Diseases, Maastricht University Medical Center, Maastricht, Netherlands. 9 Department of Medical Oncology, Centro Integral Oncologia Clara Campal, Madrid, Spain. 10 Department of Medical Oncology, Vall d'Hebron University Hospital, Barcelona, Spain. 11 Department of Medical Oncology, University Hospital Geneva, Geneva, Switzerland. 12 Department of Pulmonary Medecine, Erasmus MC
Cancer Institute, Rotterdam, Netherlands. 13 Department of Surgery, Oncology and
Gastroenterology, Instituto Oncologico Veneto IRCCS, Padova, Italy. 14 National and Kapodistrian University of Athens, Frontier Science Foundation-Hellas, Athens, Greece. 15 Department of Medical Oncology, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland. 16 Department of Nuclear Medicine, University Hospital Zürich, Zürich, Switzerland. 17 Department of Diagnostic and Interventional Radiology, University Hospital Zürich, Zürich, Switzerland Purpose/Objective: Stereotactic radiotherapy (SBRT) is increasingly adopted to treat oligometastatic non-small cell lung cancer (NSCLC) patients. Imaging-based response patterns of oligometastases after SBRT alone are well- defined; but remain unclear when combined with immunochemotherapy. This analysis of the ETOP 18- 14 CHESS trial evaluated longitudinal imaging changes after SBRT for lung and bone oligometastases in
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