68Ga-PSMA PET/CT-based metastasis-directed radiotherapy for oligometastatic prostate cancer recurrence after radical prostatectomy

Purpose: The aim of this communication was to assess the efficacy of directed oligometastatic radiotherapy (RT) based on Ga-68-PSMA PET/CT in patients with prostate cancer (PCa) biochemical relapse (BCR) after primary treatment with curative intent. Methods: This is a retrospective analysis of a monocentric cohort of PCa patients diagnosed with oligometastatic disease on Ga-68-PSMA PET/CT and treated with metastasis-directed RT. Inclusion criteria were: histologically proven PCa, BCR after primary treatment with curative intent, oligometastatic disease defined as <= 3 metastatic lesions. To evaluate the efficacy of the therapy, biochemical response defined as a decrease of > 50% of PSA (PSA(50)) was measured at 1 and 4 months. Patients were followed up until progression and start of androgen deprivation therapy (ADT). BCR-free survival and ADT-free survival were calculated. Results: 20 patients met the inclusion criteria. Median PSA value: 1.4 ng/ml (IQR, 0.3-2.3 ng/ml). A total of 30 PSMA-positive lesions were treated: 18 lymph nodes (60%), nine bone (30%) and three visceral lesions (10%). Median follow-up was 15 months (range 4-33 months). Biochemical response at 1 and 4 months was found in 3/20 patients (15%) and 14/20 (70%), respectively. BCR-free survival rate at 1 year was 79% and 53% at 2 years. ADT-free survival at 2 years was 74%. Conclusion: This retrospective study suggests that metastasis-directed RT based on Ga-68-PSMA PET/CT may be a valuable treatment in patients with PCa oligometastatic disease, providing promising BCR-free survival rates and potentially postponing ADT for at least 2 years in 74% of the patients. Response assessment should not be measured before 4 months after treatment.