Objective: Innovation is an important driver for improving the quality of health care, yet a tension exists between innovation and providing cost-effective health care. To develop strategies that promote innovation, parameters are needed that are indicative of innovation. However, no recognised indicators of innovation in radiotherapy are currently available. The aim of this study is to fill that gap by providing a framework for measuring innovation. This should facilitate future multi-centric studies on strategies aimed at promoting innovation in radiotherapy.Methods: We applied the Delphi method in four rounds. The chairpersons of all Dutch radiotherapy departments were asked to suggest indicators. The resulting inventory was assessed by a number of Dutch radiation oncologists, medical physicists and managers. After implementig a cut-off score on suitability and measurability, we asked Dutch professors on innovation to assess the remaining indicators. Finally, the chairpersons reached consensus.Results: On the basis of the Delphi study, we derived 13 indicators in four categories, more specific product innovation, technology innovation, market innovation and organisational innovation, for measuring both incremental and radical innovations in radiotherapy; these indicators are also suitable for measuring the generation and adoption of innovations.Conclusions: We were successful in reaching consensus amongst the experts on indicators that measure innovations in radiotherapy. The developed tool will be used to investigate the relation between innovation and possible factors inhibiting or stimulating successful innovation and between the level of innovation and its effects.