ESTRO-EORTC expert guideline on target delineation and radiotherapy details for stage I–III small cell lung cancer

INTRODUCTION: Stage I-III limited-stage small cell lung cancer (SCLC) is a highly aggressive yet potentially curable disease with concurrent chemoradiotherapy. Thoracic radiation therapy (RT) plays a central role in the management of stage I-III SCLC; however significant variation exists in staging, target volume delineation, dose prescription, and integration with systemic therapy. This document provides an updated European recommendations on the use of RT in stage I-III SCLC, reflecting recent evidence and advancements in clinical practice. MATERIAL AND METHODS: A panel of European experts was convened under the auspices of the ESTRO Guidelines Committee, in collaboration with EORTC Lung Cancer Group, and to review the available evidence and develop recommendations. Key topics addressed included disease staging, radiotherapy planning and delivery, and the integration with chemotherapy and immunotherapy. RESULTS: Accurate staging should include PET-CT and brain MRI. Thoracic RT should be initiated early during chemotherapy. Standard dose schedules include 45 Gy in 30 fractions (BID) or 66 Gy in 33 fractions once daily, using conformal techniques such as IMRT/VMAT, involved field nodal irradiation, respiratory motion management (e.g., 4D-CT, breath-hold) and image guidance (e.g., cone-beam CT [CBCT]). Concurrent chemotherapy with 4-6 cycles platinum-etoposide followed by consolidation durvalumab for up to two years is the standard of care in fit patients. Prophylactic cerebral irradiation (PCI) continues to represent the standard approach following treatment response; while hippocampal-sparing PCI and MRI surveillance strategies are being actively evaluated in ongoing studies. In selected cases, stereotactic body radiotherapy (SBRT) may be appropriate for medically inoperable early-stage disease without nodal involvement, and adjuvant RT can be considered for R1 resections or pN2 involvement. Emerging strategies, including adaptive RT, dose escalation and the integration of precision medicine have the potential to improve the therapeutic ratio. Integration with immunotherapy and/or novel agents, such as delta-like ligand 3 (DLL3)-targeted therapies, is under active investigation. Biomarker-guided treatment personalisation remains investigational. CONCLUSIONS: These updated European guidelines provide a comprehensive framework for standardized, high-quality care in stage I-III SCLC and establish a reference standard to harmonize radiotherapy approaches and inform the design of upcoming clinical trials.