S842
Clinical - Lung
ESTRO 2026
one year after radiotherapy (RT), grade ≥ 2 AET during or within four weeks after RT, and 2yM from RT start. Results: Median age was 67 years (range: 31 – 84), and 49% had stage IIIB disease. Concurrent CRT was delivered in 81%, and 78% received durvalumab. Median RT dose was 60 Gy. IMPT was the primary modality, but 81% of patients received some VMAT fractions (median 4, IQR: 2 – 7). Median total GTV was 81 cm3 (IQR: 43 - 145); median MLD, MED, and MHD were 12 Gy (IQR: 9.4 – 15), 18 Gy (IQR: 11 – 27), and 4.2 Gy (IQR: 2.5 – 6.8), respectively. Model-based selection was primarily driven by predicted reductions in 2yM, either alone (81%) or combined with RP (8.5%) or AET (4.6%). Waterfall plots (Figure 1) show individual predicted NTCP benefit, with the largest expected benefit for 2yM. Among evaluable patients, RP occurred in 18%, AET in 45%, and 2yM in 37% (Table 1). Observed RP and 2yM rates were lower than predicted by VMAT- based NTCP, while AET was higher (Table 1).
Conclusion: This is the first study assessing longitudinal FDG- PET/CT changes in NSCLC oligometastases treated with SBRT and concomitant immunochemotherapy. Most bone and lung metastases showed early metabolic response, without atypical morphological changes up to 12 months after pulmonary SBRT. Keywords: Oligometastases, SBRT, immunotherapy Digital Poster Highlight 4372 Outcomes of intensity-modulated proton therapy in unresectable stage III NSCLC treated with chemoradiotherapy in the durvalumab era Kyra A.L. van Keeken 1 , Robin Wijsman 2 , Lisanne van Dijk 2 , Robert van der Wal 2 , Stephanie Peeters 1 , Dirk de Ruysscher 1 , Valery Lemmens 3 , Judith van Loon 1 1 Radiation Oncology, MAASTRO, Maastricht, Netherlands. 2 Radiation Oncology, University Medical Center Groningen, University of Groningen, Groningen, Netherlands. 3 GROW Research Institute for Oncology and Reproduction, Maastricht University Medical Centre+, Maastricht, Netherlands Purpose/Objective: Proton therapy offers dosimetric advantages over photon therapy in stage III NSCLC (1), yet clinical evidence on toxicity and survival outcomes, especially in the durvalumab era remains limited (2). This study evaluated the results of IMPT for model-based selection, and radiation pneumonitis (RP), acute esophageal toxicity (AET), and two-year all-cause mortality (2yM) in patients with stage III NSCLC treated with chemoradiotherapy (CRT). Material/Methods: We retrospectively analyzed prospectively collected data from 259 patients with stage III NSCLC treated with sequential or concurrent CRT and IMPT between 2019–2024. For each patient, VMAT and IMPT plans were compared using NTCP-models; IMPT was selected if Δ NTCP thresholds were met: ≥ 10% for RP or AET, ≥ 15% for combined RP + AET, or ≥ 2% for 2yM (3, 4). Dosimetric parameters in these models are: Mean Lung Dose (MLD) for RP, Mean Esophagus Dose (MED) for AET, and Mean Heart Dose (MHD) for 2yM. Endpoints were the incidence of grade ≥ 2 RP within
Conclusion: IMPT for stage III NSCLC in the durvalumab era was associated with toxicity rates comparable to historical photon-based CRT cohorts, supporting its safety. Observed RP and AET rates were consistent with NTCP model predictions, while 2yM was lower than predicted, likely reflecting improved survival with adjuvant durvalumab, which current models do not account for. To establish the potential advantage of IMPT over VMAT, comparative analyses with matched photon cohorts are needed. References: 1.Dionisi F, et al. Dosimetric and NTCP advantages of robust proton therapy over robust VMAT for Stage III NSCLC in the immunotherapy era. Phys Med. 2024;123:103410.2. Lin-Liu Y, et al. Isolated nodal failure in stage III non-small-cell lung cancer after proton therapy with or without durvalumab. Radiother Oncol. 2025;209:110990.3. NVRO. Landelijk Indicatieprotocol Protonentherapie
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