A 72-year-old man was diagnosed 9 years ago with prostate cancer. After radiation treatment, his prostate-specific antigen (PSA) level dropped to a nadir of 1.5 ng/mL; it had remained stable until it rose to 2 ng/mL 1 year ago and is currently 3.2 ng/mL. He has no symptoms. What is the most appropriate next step in management?