The drug being tested in this study is called TAK-385. Men with prostate cancer benefit from receiving androgen deprivation therapy (ADT) to minimize testosterone levels before, during and after EBRT. This combination increases the potential success of treating their disease. This study will see if TAK-385 [an oral gonadotropin-releasing hormone (GnRH) antagonist] brings testosterone levels down sufficiently, with the convenience and comfort of taking a pill. It will look at the time it takes to restore testosterone levels after radiation therapy as well. One hundred participants will be assigned by chance (like flipping a coin) to a treatment group: 60 to TAK-385, and 40 to degarelix.