This is an National Institute of Health (NIH) funded, investigator-initiated, single center prospective study to investigate the ability of the new dual-modality positron emission tomography and computed tomography (PET-CT) imaging systems in comparison to conventional imaging methods in assessing treatment response in men with metastatic prostate cancer. The investigators will enroll two groups of men with stage IV metastatic prostate cancer, each group will be comprised of 160 patients.