Men with microscopic evidence of prostate cancer spreading to their pelvic lymph nodes (LNs) following the surgical resection of the prostate and pelvic lymph nodes (LN) are at a very high risk of dying from prostate cancer. Pelvic LN radiation therapy (RT) is a potentially curative treatment. However, no randomized clinical trials have been conducted in men with pN1 prostate cancer to evaluate whether survival is prolonged via pelvic LN RT when the post-operative prostate-specific antigen level is undetectable (i.e., adjuvant) versus the current standard of care, which involves waiting until the PSA becomes detectable (i.e., early salvage).