Clinical evidence and reporting standards in reirradiation: Insights from 28 studies at ESTRO 2025, endorsed by the ESTRO reirradiation focus group.

Background: Reirradiation (reRT) has become an increasingly relevant treatment option across multiple tumor sites, supported by technological advances that improve precision and safety. At the ESTRO 2025 Annual Meeting, 28 clinical studies on reRT were presented. This work provides a structured synthesis of their clinical outcomes and assesses adherence to the ESTRO-EORTC reporting recommendations. Materials and methods: All abstracts presented at ESTRO 2025 (n = 2,962) were screened to identify reRT studies (n = 51). Only studies reporting at least one clinical outcome were retained (n = 28). ReRT was classified as type 1 (with geometric overlap of irradiated volumes) or type 2 (without overlap but with potential OAR dose concerns). Each study was evaluated using the 10 mandatory ESTRO-EORTC reporting criteria, covering demographics, performance status, organ function, recurrence classification, target volume, technique and dose, interval since RT1, cumulative OAR doses, method for dose summation, and CTCAE toxicity. Reporting scores ranged from 0 to 10. Results: The 28 studies encompassed brain, head and neck, thoracic, pelvic, prostate, metastatic, and pediatric settings. Clinical outcomes were encouraging in selected series, with local control > 85 % in the phase I DESTROY-1 dose-escalation trial, median overall survival > 40 months in lung and prostate cohorts, and grade ≥ 3 toxicity generally below 10 %. Reporting quality was heterogeneous: the median score was 5/10 (IQR 4-7). Demographics, prescribed dose, and technique were consistently reported, whereas organ function, cumulative OAR doses, and methods for dose summation were often omitted. Classification as type 1 or type 2 reRT was explicitly provided in only a minority of abstracts. Items such as baseline organ function were often missing, particularly in CNS studies where standardized tests are rarely applicable. Conclusion: The ESTRO 2025 abstract set illustrates both the clinical potential and methodological variability of modern reRT. While outcomes are promising across several sites, adherence to standardized reporting remains limited, underscoring the need for consistent implementation of ESTRO-EORTC recommendations to enable comparability and harmonization.