ESTRO 2025 - Abstract Book

S1055

Clinical – Head & neck

ESTRO 2025

6 Department of Radiation Oncology, Hospital Universitario Ramon y Cajal, Madrid, Spain. 7 Department of Radiation Oncology, Biocruces Bizkaia Health Research Institute and Cruces University Hospital, Barakaldo, Vizcaya, Spain. 8 Department of Radiation Oncology, Azienda Ospedaliero-Universitaria Careggi, Florence, Italy. 9 Department of Biomedical Sciences, Humanitas University, Milan, Italy. 10 Department of Radiotherapy and Radiosurgery, IRCCS Humanitas Research Hospital, Milan, Italy. 11 Department of Radiation Oncology, Fondazione IRCCS Istituto Nazionale dei Tumori di Milano, Milan, Italy. 12 Department of Medical Oncology, IRCCS Humanitas Research Hospital, Milan, Italy. 13 Department for Radiation Oncology, Ghent University Hospital and Ghent University, Ghent, Belgium. 14 Radiation Oncology Department, Cliniques Universitaires Saint-Luc, Brussels, Belgium. 15 Kortrijk Cancer Centre, General Hospital Groeninge, campus loofstraat, Cancer Centre, Kortrijk, Belgium. 16 Institute of Radiation Oncology, Cantonal Hospital of Graubünden, Chur, Switzerland. 17 Department of Radiation Oncology, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland. 18 Center for Radiation Oncology KSA, Cantonal Hospital Aarau, Aarau, Switzerland. 19 Clinic of Radiotherapy and Radiation Oncology, University Hospital Basel, Basel, Switzerland. 20 Department of Radiation Oncology, Cantonal Hospital Winterthur, Winterthur, Switzerland. 21 Radiation Oncology, Oncology Institute of Southern Switzerland (IOSI), EOC, Bellinzona, Switzerland. 22 Department of Medical Physics, Institut Jules Bordet, Brussels, Belgium. 23 EORTC Headquarters, Avenue Emmanuel Mounier 83/11, 1200, Brussels, Belgium. 24 Department of Medical Oncology, Cliniques Universitaires Saint-Luc, Brussels, Belgium. 25 Department of Medical Oncology, Université Catholique de Louvain, Louvain-la-Neuve, Belgium. 26 Department of Radiation Oncology, University Hospital Zurich, University of Zurich, Zurich, Switzerland Purpose/Objective: Stereotactic ablative radiotherapy (SABR) is integrated as treatment option for various clinical situations and already practiced for the ablation of oligometastases in squamous cell carcinoma of the head and neck (SCCHN). However, the added value of SABR in addition to modern immunotherapy for this indication remains unclear and there exists no high-level evidence supporting this modality. Material/Methods: 200 patients with 1-5 synchronous or metachronous metastases of SCCHN and a PD-L1 CPS ≥1 will be treated with pembrolizumab (400 mg i.v., Q6W) for 2 years in both arms and randomized to receive palliative radiotherapy only where necessary (e.g. if symptomatic) in the standard arm (Arm 1) and SABR to the oligometastatic lesions in the experimental arm (Arm 2). Primary endpoint is progression free survival (PFS) and secondary endpoints overall survival, local control of treated metastases and a comprehensive evaluation of the quality of life implementing a specifically compiled item collection. A rescaling of the DVHs from the collected RT plans will be performed to investigate a potential cause-effect relationship between the prescription method for lung metastases and outcomes. Techniques Radiotherapy Quality Assurance (RTQA) procedures are aligned with the EORTC 1945 OligoRare trial to facilitate future data pooling. Pre-trial procedures include a questionnaire, to identify intended treatment techniques, and a phantom audit. All patient digital treatment data, including imaging used to aid radiation planning and radiotherapy planning eCRF must be submitted prior to the start of RT. The first plan per institution in the experimental arm is reviewed prospectively, the following retrospectively. Uniform structure naming per AAPM TG 263 is required. Imaging for planning, localization, verification, and prescription doses and constraints for organs at risk follow the EORTC 1945 OligoRare and COMET-3 trials. Dose constraints take priority, allowing target coverage compromise if necessary. All treatments will be applied in 1-8 fractions. The ancillary sub-study will compare the heterogeneity of actual tumor dose for two prescription methods (to the PTV vs. GTV) and determine TCP models with associated uncertainties (introduced by this inter-patient dose heterogeneity) in patients receiving SABR to lung lesions. Conclusion: The EORTC 2014-HNCG PROLoNg (EU Trial 2023-504478-39; NCT05815927) is a randomized, phase III, open label trial that will be launched in 2025 in four countries (Belgium, Italy, Spain, Switzerland) and aims to be the first multicentric, international effort to provide high-level evidence for the combined approach of SABR and immune checkpoint inhibitors for oligometastatic SCCHN under strict quality assurance for radiotherapy.