As cancer survivors live longer, technologies improve, and reirradiation (reRT) becomes more common, standardised methods for the assessment and reporting of cumulative radiation doses are needed to allow treatment optimisation and integration with other medical specialties managing these complex patients. This consensus statement, developed by an international collaboration of radiation oncologists, physicists, and other experts in the Reirradiation Collaborative Group, proposes a framework for consistent evaluation, documentation, reporting, and clinical decision making in reRT. This paper outlines practical strategies for dose accumulation from multiple courses of radiation therapy with the use of both image registration-based and point dose-based methods, accounting for uncertainties in data availability, physiological organ recovery, and anatomical changes. The emphasis of the consensus statement is on institutional workflows, improved software tools, and better capture of longitudinal patient outcomes. We also highlight the need for improved biological models, data infrastructure, and cross-specialty collaboration. Ultimately, reRT is framed as a transformative challenge for oncology, demanding interdisciplinary innovation across science, clinical care, and health systems. Widespread adoption of these recommendations could accelerate progress toward improved outcomes for patients receiving reRT worldwide.