This study investigates the effects of combining radium-223 with a chemotherapy treatment called docetaxel in patients with prostate cancer that has spread to the bones. The study aims to compare the outcomes of this combination treatment with those of using docetaxel alone. Prostate cancer is a condition where cancer cells form in the tissues of the prostate, and when it spreads to other parts of the body, it is known as metastatic prostate cancer. Radium-223 is a type of radioactive substance that targets bone metastases, which are cancerous growths in the bone.

Participants in this study will receive either the combination of radium-223 and docetaxel or docetaxel alone. The study will involve monitoring the effects of the treatments on the participants' health and cancer progression. Participants will be required to follow specific guidelines regarding birth control and will not be allowed to donate sperm during the study and for a period after the study ends. The study will also monitor for any side effects or changes in the participants' condition.

• Who can participate: Men with prostate cancer that has spread to the bones and is progressing despite previous treatments can participate. Participants must have two or more bone lesions, have normal organ function, and agree to use birth control methods.
• Study details: Participants will receive either radium-223 combined with docetaxel or docetaxel alone. They must follow birth control guidelines and cannot donate sperm during the study and for 30 days after. A placebo is not used in this study.