In the phase 3 , randomised , double-blind ALSYMPCA trial , patients with symptomatic castration-resistant prostate cancer , at least two symptomatic bone metastases , no known visceral metastases , and who were receiving best standard of care were randomly assigned ( 2:1 ) via an interactive voice response system to receive six injections of radium-223 ( 50 kBq/kg intravenously ) or matching placebo , with one injection given every 4 weeks .