BACKGROUND AND PURPOSE:Quality indicators (QIs) have been developed for many aspects of prostate cancer care, but are under-developed with regard to radiotherapy treatment. We aimed to develop a valid, relevant and feasible set of core QIs to measure quality of radiotherapy care in men with prostate cancer. MATERIALS AND METHODS:We used a RAND-modified Delphi process to select QIs that were regarded as both important and feasible measures of quality radiotherapy care. This involved two phases: (1) a literature review to identify a list of proposed QIs; and (2) a QI selection process by an expert panel (n = 12) conducted in a series of three rounds: two online questionnaires' and one face-to-face meeting. The RAND criterion identified variation in ratings and determined the level of agreement after each round of voting. RESULTS:A total of 144 candidate QIs, which included measures from pre-treatment to post-treatment and survivorship care were identified. After three rounds of voting, the panel approved a comprehensive set of 17 QIs, with most assessing a process of care (n = 16, 94.1%) and the remaining assessing a health outcome. CONCLUSION:This study developed a core set of 17 QIs which will be used to report from the Prostate Cancer Outcomes Registry-Australia & New Zealand, to monitor the quality of radiotherapy care prostate cancer patients receive.