68Ga-PSMA Ligand PET/CT-based Radiotherapy for Lymph Node Relapse of Prostate Cancer After Primary Therapy Delays Initiation of Systemic Therapy

Aim: To evaluate 68Ga-PSMA ligand positronemission tomography-computed tomography (PET/CT)based radiotherapy for lymph node metastases of prostate cancer after primary therapy. Patients and Methods: Twentythree patients received radiotherapy for PSMA ligand positive lymph node metastases. Results: The median followup time was 12.4 (range=6.0-28.5) months. The median pretreatment prostate-specific antigen (PSA) decreased from 2.75 (range=0.52-8.92) ng/ml to a nadir of 1.37 (range=0.11-8.00) ng/ml (p=0.001) following radiotherapy. Except for one patient (4.4%), PSA level decreased in 22 patients (95.6%). The biochemical failure-free survival and time to initiation of systemic therapy at the median followup were 95.6% and 100%, respectively. Three patients (12.9%) presented with recurrent disease outside the initial radiation field. No grade III acute toxicities or late grade II toxicities were observed. Conclusion: Ga-68-PSMA ligand PET/CT-based radiotherapy is a promising local treatment option for isolated lymph node metastases of prostate cancer.