PSMA-PET Guided De-escalation of Salvage Radiation Treatment in Recurrent Prostate Cancer

Purpose: Prospective, single-site Phase II study testing whether PSMA-PET/MRI-guided, de-escalated salvage radiation reduces acute Grade ≥2 toxicity versus a 44% historical rate, while maintaining cancer control after prostatectomy.Population/Eligibility: Adult men ≥30 years with prior radical prostatectomy and biochemical persistence/recurrence per NCCN (persistent positive PSA after RP, or undetectable PSA that becomes detectable and rises on ≥2 determinations, or PSA \>0.1 ng/mL). Must have a targetable PSMA-avid lesion in the prostate bed and/or pelvic lymph nodes and/or an MRI-defined lesion suspicious for local recurrence. KPS ≥80 or ECOG ≤2; life expectancy \>5 years; able to consent. Exclude: Evidence of distant metastatic disease outside pelvic nodes (including osseous involvement), conditions that preclude radiation, or factors preventing protocol compliance.Interventions \& Evaluations: Baseline history/physical, vitals, performance status, labs (PSA, CBC w/diff, CMP/creatinine), pelvic MRI and PSMA-PET/CT; optional biopsy if feasible. External beam radiation therapy (LINAC/VMAT) with daily image guidance: pelvis 45 Gy in 25 fractions, followed by a sequential boost to PSMA/MRI-defined disease to 63-70.2 Gy in 10-14 additional fractions, with protocolized OAR constraints. All participants receive standard-of-care androgen deprivation therapy (ADT) for 6-24 months at the treating clinician's discretion. Weekly on-treatment visits; physician-assessed toxicities graded by CTCAE v5. Patient-reported outcomes (IPSS; FACT-P) at baseline and each in-person follow-up.Follow-up: Phone toxicity check 1 month post-RT; clinic at 4 months post-RT, then every 3 months thereafter until 24 months after completion of ADT. At each visit: H\&P, CTCAE toxicity assessment, and PSA. If biochemical failure occurs, imaging (PSMA-PET/CT, CT and/or MRI) is obtained per standard of care to assess clinical progression.Endpoints/Design: Primary endpoint: acute (≤4 months post-RT) Grade ≥2 toxicity (all types). Secondary endpoints: 2-year biochemical progression-free survival; chronic toxicity and patient-reported outcomes from 4-24 months; 24-month local control, locoregional control, distant metastasis, and overall survival. Simon optimal two-stage design with interim analysis after the first 18 patients complete RT (stop if ≥8 have Grade ≥2 acute toxicity); total planned enrollment up to 54.

Inclusion Criteria: 1. Prior biopsy proven prostate cancer for which they underwent a radical prostatectomy with curative intent. 2. Evidence of biochemical recurrence as defined by NCCN: Persistent positive PSA post-radical prostatectomy (RP) or an undetectable PSA after RP with a subsequent detectable PSA that increases on ≥2 determinations (PSA recurrence) or increases to PSA \>0.1 ng/mL. 3. Targetable PSMA-avid lesion within the prostate bed, pelvic lymph nodes, or both and/or targetable lesion in prostate bed defined on MRI suspicious for local recurrence. 4. If lesions are amenable for biopsy this may be attempted, but biopsy proven recurrence/persistence is not required for trial enrollment. 5. Life expectancy greater than 5 years. 6. Karnofsky performance status ≥ 80 or Eastern Cooperative Oncology Group performance status ≤ 2 within 14 days prior to registration. 7. Age ≥ 30 years. 8. Patient must be able to provide study-specific informed consent prior to study entry. Exclusion Criteria: 1. Evidence of distant metastatic disease outside the pelvic lymph nodes (including osseous pelvic disease). 2. Presence of any psychological, familial, sociological, or geographical condition potentially hampering compliance with the study protocol and follow-up schedule, including alcohol dependence or drug abuse. 3. Relative or absolute contraindications to radiation therapy as determined by the treating physician. These include but are not limited to inflammatory bowel disease, connective tissue disorders (systemic lupus erythematosus, scleroderma, etc.), and genetic disorders that risk increased sensitivity to radiation therapy.