ESTRO 2025 - Abstract Book

S1358

Clinical - Lung

ESTRO 2025

of Radiation Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom. 11 Division of Molecular and Cancer Sciences, University of Manchester, Manchester, United Kingdom. 12 Thoracic Oncology, Institute of Cancer Research, London, United Kingdom. 13 Department of Clinical Oncology, Guy’s and St Thomas’ NHS Foundation Trust, London, United Kingdom. 14 Department of Clinical Oncology, Queen Elizabeth Hospital, Birmingham, United Kingdom. 15 Department of Clinical Oncology, Bristol Royal Infirmary, Bristol, United Kingdom. 16 Department of Clinical Oncology, University College London Hospitals NHS Foundation Trust, London, United Kingdom. 17 Department of Oncology, University College London, London, United Kingdom. 18 Department of Medical Oncology, University College London Hospitals NHS Foundation Trust, London, United Kingdom. 19 Department of Clinical Oncology, Addenbrookes Hospital, Cambridge, United Kingdom. 20 Edinburgh Cancer Centre, Western General Hospital, Edinburgh, United Kingdom. 21 School of Cancer Sciences, University of Glasgow, Glasgow, United Kingdom. 22 Department of Clinical Oncology, University Hospital Southampton, Southampton, United Kingdom. 23 Northern Centre for Cancer Care, The Newcastle Upon Tyne Hospitals NHS Foundation Trust, Newcastle, United Kingdom Purpose/Objective: SARON is a Phase II randomised (1:1) controlled trial (N=140), comparing radical radiotherapy (RT) alongside standard systemic anti-cancer therapy (SACT) to SACT alone, in patients with synchronous oligometastatic (OM) non small cell lung cancer (NSCLC). Intervention arm patients received either conventionally fractionated radiotherapy (CFRT) or stereotactic ablative radiotherapy (SABR) to the lung primary +/- locoregional lymph nodes, and SABR or stereotactic radiosurgery (SRS) to OM sites. The thoracic SABR safety sub-study (TSSS) within SARON, focuses on patients treated with CFRT to the lung primary (+/- lymph nodes) and SABR to thoracic metastases. There is limited safety data with this combination of differing fractionation schedules within the thorax. Here, we report acute adverse events and explore dosimetric predictors of toxicity in the SARON TSSS. Material/Methods: Acute RT-related toxicity (up to 3-months post-RT) was assessed using the Common Terminology Criteria for Adverse Events version 4.03. Organ-at-risk (OAR) doses were converted to biological effective doses (BED) for CFRT and SABR plans (α/β=3, except spine α/β=2), followed by dose summation to calculate the combined OAR BED. This was performed using VelocityAI software (Varian Medical Systems, Palo Alto, CA). All data are descriptive in nature. Results: Of the 70 patients with synchronous OM-NSCLC randomised to the SARON investigational arm, 13 were treated in the TSSS. TSSS patients had a median age of 68 years (IQR 62-71), 62% (n=8) female, 62% (n=8) with a performance status of 0, and 62% (n=8) with single-site metastasis. Twenty metastatic sites were treated with SABR, including 14 thoracic metastases: 5x thoracic spine, 4x lung, 3x scapula, 2x rib. The most common SABR and CFRT fractionation schedule was 27 Gy/3Fr (4/14) and 55 Gy/20Fr (10/13), respectively. No grade 3 or higher RT-related acute toxicities were reported. Grade 2 acute oesophageal toxicity occurred in 38% (n=5), radiation-induced lung toxicity in 15% (n=2), chest wall pain in 15% (n=2), fatigue in 8% (n=1), and nausea/vomiting in 8% (n=1). Those with grade 2 acute oesophageal toxicity (n=5) had higher median combined oesophageal BED3 compared to those without (n=8): 111 Gy vs. 93 Gy (Dmax), 104 Gy vs. 75 Gy (D0.5cc), and 81 Gy vs. 53 Gy (D5cc). Conclusion: CFRT to the lung primary +/- lymph nodes and SABR to thoracic metastases in synchronous OM-NSCLC is feasible with few acute RT-related adverse events observed, and no grade ≥3. Five patients experienced grade 2 oesophageal toxicity, having received higher combined BED3 doses than those without.