• Histologically confirmed adenocarcinoma of the prostate without neuroendocrine differentiation or small cell features;

• M0CRPC at study entry defined as follows:

‣ Ongoing androgen deprivation therapy with a LHRH agonist or bilateral orchiectomy (i.e., surgical or medical castration);

⁃ Serum testosterone level ≤ 1.7 nmol/L (50 ng/dL) at the Screening visit;

⁃ PSA progression defined by a minimum of two subsequent rising PSA levels with an interval of ≥ 1 week between each determination. Patients who received an anti-androgen must have progression after withdrawal (≥ 4 weeks since last flutamide or ≥ 6 weeks since last bicalutamide or nilutamide). The PSA value at the Screening visit should be ≥ 2 μg/L (2 ng/mL)

⁃ PSA doubling time of 10 months or less,

⁃ M0 assessed by conventional imaging (CT/MRI + bone scan).

∙ NOTE: If darolutamide started prior to study entry, evidence of inclusion criteria 1-5 listed above prior to start of darolutamide must be submitted to determine study eligibility

• Prior cytotoxic chemotherapy for prostate cancer in adjuvant setting post radical therapy is allowed;

• Eastern Cooperative Oncology Group (ECOG) performance status of 0-1 or Karnofsky performance status of \> 80% or higher;

• Estimated life expectancy of ≥ 6 months;

• Ability to swallow the study drug whole and comply with study.

• Patients should not have been previously exposed to other ARATs (Abiraterone, Enzalutamide, Apalutamide)

• ≤ 5 metastatic sites (on conventional imaging);

• ≤ 4 tumors within any given organ system, excluding brain (e.g. up to 4 bone metastases, or 4 lung metastases);

• All sites of disease must be amenable to SBRT with no history of the metastases being irradiated (radiation exposure prior to the development of the metastases is permitted as long as the radiation exposure was not intended for the metastases. For example, if there is prior pelvic radiation to the prostate and a subsequent iliac metastasis develops within the previously irradiated pelvic radiation field, then the iliac metastasis would be eligible per the institution policy and practice);

• In the case of a suspicious lesion in an unusual location such as lung or thoracic lymph nodes (without other abdominal lymph nodes), a confirmatory imaging or biopsy is strongly recommended;