Background: ORIOLE is a randomized, non-blinded Phase II interventional study evaluating the safety and efficacy of SBRT in biochemically recurrent, oligometastatic, hormone-sensitive prostate cancer at 3 centers in the US. Patients will be stratified by clinical characteristics and randomized 2:1 to SBRT or observation. The primary clinical endpoint is progression at 6 months defined by PSA increase, radiologic or clinical evidence, ADT initiation, or death from any cause. Secondary endpoints include local control at 6 months, SBRT-associated toxicity and quality of life, and ADT-free survival. Imaging and laboratory correlates will characterize, in isolation, the effects of SBRT on oligometastatic disease. Methods: Eligible patients are hormone-sensitive, have undergone prior definitive treatment and recurred with 1-3 asymptomatic bone or soft tissue metastases diagnosed within 6 months, PSA doubling time (PSADT) < 15 months, ECOG performance status ≤ 2, and normal organ and marrow function. Minimization will be used to balance assignment by primary intervention, prior ADT, and PSADT. Accrual of 54 patients provides 85% power to detect a decrease in progression rate from 80% to 40% with type I error = 0.05 using one-sided Fisher’s exact test. Hazard ratios and Kaplan-Meier estimates of progression free survival, ADT free survival, and time to locoregional and distant progression will be calculated based on intention-to-treat. Local control will be assessed using RECIST 1.1 criteria. Withdrawal prior to 6 months will be counted as progression. Adverse events will be summarized and quality of life pre- and post-SBRT will be measured by Brief Pain Inventory. The investigational targeted imaging agent ¹⁸F-DCFPyL will be compared to bone scan and CT for identifying oligometastases before SBRT and monitoring disease response following SBRT. Biological alterations induced by SBRT will be investigated using circulating tumor cell analysis, deep sequencing of circulating tumor DNA, and T-cell repertoire profiling. A hereditary cancer assay will inform efforts to advance personalized screening and therapy. Clinical trial information: NCT02680587