Published in the Red Journal, this study was set to establish an expert consensus regarding prerequisites, study design, and endpoints for the next clinical trials of proton FLASH in humans. An international expert panel of 21 clinicians, physicists, and biologists, with well-balanced in expertise and geography, were asked to complete a set of questionnaires. A strong agreement was reached that an ablative setting to oligometastatic disease can be used, in addition to the palliative setting. The proton FLASH effect should be studied in a single treatment modality setting with toxicity reduction as the primary endpoint.