Cumulative dose evaluation in clinical reirradiation – Consensus guidance on technical considerations by the ESTRO reirradiation focus group

Reirradiation is increasingly used, but its safe application requires accurate evaluation of cumulative doses to organs at risk. Methods of cumulative dose evaluation vary widely, from simple summation of prescription doses to complex three-dimensional (3D) dose summation methodologies, yet best practices remain undefined. This guidance, endorsed by the ESTRO Reirradiation Focus Group, provides detailed recommendations on the technical aspects of 3D dose summation; appropriate alternatives when it is unfeasible, suboptimal, or requires special considerations; and general guidance on uncertainty evaluation, resource management, and implications for treatment delivery. The writing group (n = 15) analysed scenarios ranging from full 3D dose summation to situations with incomplete data and unacceptable image registration, and developed recommendations through structured expert discussion and a two-step voting process. Key discussion points included: dose mapping (with rigid and deformable image registration), radiobiological corrections (particularly equieffective dose rescaling, such as EQD2Gy and BED), uncertainties, role of documentation, quality control, and peer review. Thirty-five statements reached consensus within both the writing group and the full ESTRO Physics Reirradiation Working Group (n = 34, 66 % response rate). Altogether, this guidance offers a practical framework for standardizing the technical aspects of cumulative dose evaluation to support clinical decision making and improve safety and effectiveness of reirradiation, while reducing institutional variability. It also highlights ongoing needs for research into advanced dose mapping, image registration, and integration of uncertainty analyses.