This clinical trial is for men age 18 and older with metastatic castration-resistant prostate cancer (mCRPC), which is prostate cancer that no longer responds to hormone therapy. The cancer spreads (metastasizes) to the bones. 

The primary objective of this study is to compare overall survival of subjects treated with docetaxel versus those treated with docetaxel plus radium-223. Radium-223 targets bone metastases and emits low levels of radiation, limiting damage to the surrounding tissues. 

Randomization arms: 

• Arm A- Docetaxel will be administered every three weeks at 75mg/m2 through IV for 10 doses. Prednisone will be administered at 5mg orally twice daily. Dexamethasone and growth factor support will be given per institutional practice. 
• Arm B- Docetaxel will be administered every three weeks at 60mg/m2 through IV for 10 doses. Radium-223 will be administered at 55 kBq/kg, 6 injections at 6 week intervals. Prednisone, dexamethasone, growth factor support will be given per institutional practice. 

Length of time on treatment will vary depending on randomized arm, listed above. Safety follow-up visit will take place 4 weeks after the last dose. End of treatment follow-ups will be every 3 months until the initiation of another therapy, disease progression or death. Subjects will continue on treatment as long as they are responding to therapy and not experiencing unacceptable side effects.