Response With Interim PSMA PET in Metastatic Castration-sensitive Prostate Cancer for Optimization of Adaptive Metastasis-directed Radiotherapy Delivery

Inclusion Criteria:

1. History of pathologically confirmed prostate cancer.
2. Age \>=18 years.
3. Performance status ECOG 0-2.
4. Staging 68Ga PMSA-11 PET/CT showing 4-20 sites of metastasis from prostate cancer within \<=90 days prior to registration. This scan ideally should be performed before initiation of androgen deprivation therapy (ADT).
5. At the discretion of the treating investigator, it is believed that it is safe to treat all sites of disease using SABR.
6. All men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry, for the duration of standard of care SABR and for a period of time of 6 months thereafter as per standard guidelines. Should a patient's partner become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately.
7. Ability to understand and the willingness to sign a written informed consent.
8. Planned for standard systemic therapy for metastatic prostate cancer to include androgen deprivation therapy (ADT). Upfront Docetaxel should not be planned (See section 4.1.2).

Exclusion Criteria:

1. Prior radiotherapy to any metastases currently targeted for therapy or overlapping regions.
2. Patient with metastatic lesions involving the gastrointestinal tract, specifically, invading esophagus, stomach, or intestines will be excluded. Patients with ultra-central metastatic lesions defined as 1 cm from the trachea and main bronchi will be excluded.
3. Serious medical co-morbidities precluding safe delivering of radiotherapy to poly-metastatic sites. This includes interstitial lung disease for patients undergoing SABR to thoracic sites and ulcerative colitis or Crohn's disease requiring systemic immunosuppressive therapy for patients undergoing SABR to GI sites.
4. Subjects may not be receiving any other PSMA-directed investigational agents for the treatment of the cancer under study.
5. History of allergic reactions to PMSA-11 68Ga imaging agent.
6. Uncontrolled intercurrent illness or psychiatric illness/social situations that, in the opinion of the investigator, would limit compliance with study requirements.