Reirradiation of lower gastrointestinal Cancer: A survey of ongoing trials by the Reirradiation Collaborative group (ReCOG)

Background and purpose: Pelvic reirradiation is increasingly used for locally recurrent rectal and anal cancers, either to facilitate salvage surgery or to improve local control when surgery is not feasible. However, prospective evidence remains limited, and studies often lack sufficient methodological detail to support interpretation across trials. We aimed to identify ongoing lower gastrointestinal reirradiation trials and describe characteristics, heterogeneity, and evidence gaps. Materials and methods: The Reirradiation Collaborative Group lower gastrointestinal working group performed a registry-based search for prospective pelvic reirradiation studies in rectal and anal cancer. Eligible studies were prospective, observational or interventional trials involving reirradiation for lower gastrointestinal cancers. Principal investigators were invited to complete a structured 40-item questionnaire covering trial design, reirradiation definition, clinical intent, endpoints, use of patient-reported outcomes (PROs), radiotherapy technique, target, and cumulative dose evaluation. Results: Of 27 identified studies, 21 were eligible and investigators from 9 trials completed the questionnaire. Most trials used type 1 reirradiation (overlap of irradiated volumes) according to the ESTRO/EORTC framework, but substantial heterogeneity was observed in dose-fractionation, modality, target volume margins, organs of interest, dose objectives, and cumulative dose methodology. Toxicity was assessed with CTCAE, and most studies incorporated PROs, although instruments and timepoints varied. Based on these findings, we propose 12 pragmatic recommendations for lower gastrointestinal reirradiation trials. Conclusion: Prospective lower gastrointestinal reirradiation trials show methodological heterogeneity. Standardization of definitions, dosimetric data capture, and toxicity and PRO reporting may improve interpretability, comparability, and future evidence synthesis.