ESTRO 2025 - Abstract Book

S1763

Clinical – Upper GI

ESTRO 2025

Patient focus groups supported the proposed trial design, including inclusion of additional radiology and bloods, but highlighted need for travel expense support. 29 UK centres have completed an EOI, with good geographical spread, indicating recruitment of 100 participants per cohort/year. Conclusion: GastroSCOPE will be the first RCT to evaluate pre-emptive, high-dose RT combined with best available SACT for IGC, providing high quality, practice changing evidence. Trial design has been influenced by robust PPI and clinician involvement, anticipated to lead to good recruitment once open. Ongoing engagement with PPI research partners will continue through lifetime of the trial. References: 1.https://www.rcr.ac.uk/our-services/all-ourpublications/clinical oncology-publications/radiotherapy-dose fractionation-fourth-edition/ 2.Case et al. Gastric RT in the UK - Current Practice and Opinion on future directions. IJROBP 2023;117 2S:e286. 3.Case et al. PO-1375 A systematic review of definitive RT for inoperable, non-metastatic gastric cancer. Radioth Oncol 2023 4.Mizrak Kaya et al.101 Long-Term Survivors Who Had Metastatic Gastroesophageal Cancer and Received Local Consolidative Therapy. Oncology 2017;93:243-24 5.Hingoraniet al. Palliative RT in the Presence of Well-Controlled Metastatic Disease after Initial Chemotherapy May Prolong Survival in Patients with Metastatic Esophageal and Gastric Cancer. Cancer Res Treat 2015;14:706-1 Poster Discussion Defining the dose-volume constraints for the UK PROTIEUS oesophagus trial – ensuring a fair comparison between photons and protons Geraint J Lewis 1,2 , Owen Nicholas 3 , Ganesh Radhakrishna 4 , Lucy Faulkner 5 , Emma Patel 6 , Glenn Whitten 7 , Jonathan Helbrow 3 , Sarah Gwynne 3,2 , Maria Hawkins 8 1 Radiotherapy Physics, Velindre University NHS Trust, UK, United Kingdom. 2 Radiotherapy Trials Quality Assurance Group, Mount Vernon Cancer Centre, London, United Kingdom. 3 Clinical Oncology, South West Wales Cancer Centre, Swansea, United Kingdom. 4 Clinical Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom. 5 Radiotherapy Physics, South West Wales Cancer Centre, Swansea, United Kingdom. 6 Radiotherapy Physics, University College London Hospital, London, United Kingdom. 7 Radiotherapy Physics, The Northern Ireland Cancer Centre, Belfast, United Kingdom. 8 Clinical Oncology, University College London Hospital, London, United Kingdom Purpose/Objective: PROTIEUS is a UK randomised phase 2 study of pre-operative radiotherapy (RT) trial for oesophageal cancer, comparing photons vs protons using 40.05Gy in 15#, with toxicity as the endpoint. Data from the recently completed UK SCOPE 2 trial (dose escalated definitive CRT for oesophageal cancer) showed that, with the use of VMAT, the SCOPE 2 constraints were easily met and were therefore not considered to be reflective of current, best quality photon planning. In order to allow a valid comparison with protons, we hypothesised that we could tighten dose constraints for lungs, heart and liver for PROTIEUS. Here we describe how we defined the new constraints. Material/Methods: DVH statistics for heart, lung and liver OARs for 200 standard dose arm (50Gy/25#) SCOPE 2 cases were collated and formed the starting constraints. Proposed constraints were created using the 95 th percentile of the SCOPE 2 data for Keywords: radiotherapy, gastric, 1085