Background: Recent data has shown an overall survival (OS) benefit for up front Docetaxel or Abiraterone combined with androgen deprivation therapy (ADT) in metastatic castration sensitive prostate cancer (mCSPC). Data from STAMPEDE also suggests an additional OS benefit for radiotherapy to the prostate in men with low volume metastases. We hypothesised that Radium-223 + Radiotherapy to prostate and pelvic nodes following docetaxel (DOC) would be well tolerated and potentially improve OS in men with mCSPC involving bone. Methods: Men with mCSPC involving bone were treated in a single arm phase 1/2 study in which they received radical dose radiotherapy (74Gy/37) to prostate and pelvic nodes using Volumetric Modulated Arc Therapy (VMAT) radiotherapy and 6 cycles of Radium-223, 55kBq/kg following up front ADT and DOC. The primary endpoint was toxicity with secondary endpoints including time to PSA and ALP progression and radiological response. Results: We report the results of 27 men, median age 67 years treated in the study with a median follow up of 25 months post 1^st ADT. 81% of men had high volume disease. The schedule was well tolerated with grade ≥3 toxicity occurring in 5 patients (18.5%). Most toxicity was short lived thrombocytopenia and leucopenia. No unexpected toxicity was observed. All but 2 patients received all 6 cycles of Radium-223. One patient died of progressive disease before completion of the course of Radium-223. To date, 6 out of 27 patients have died, actuarial survival at 24 months is 83%. To date 9 out of 27 (33%) patients have developed PSA progression. Only 1 patient had a progressive alkaline phosphatase levels during the course of Radium-223 treatment. Conclusions: In men with mCSPC involving bone, a schedule of radical dose radiotherapy to prostate and pelvis + 6 cycles of Radium-223 is well tolerated post ADT + DOC. This treatment schedule will now join as a new arm of the STAMPEDE trial with OS as primary endpoint. Clinical trial information: 2014-000273-39.