Bridging to systemic therapy: PSMA-PET-based early and repetitive stereotactic body radiotherapy for nodal and bone oligo-recurrent prostate cancer

Introduction: To provide a detailed analysis regarding survival, local control and toxicity of nodal/bone oligo-recurrent prostate cancer identified and treated with PSMA-PET/CT and robotic SBRT using a uniform dose/fractionation scheme. The use of ADT was excluded. Methods: Retrospective analysis of patients with initial high-risk factors presenting with nodal/bone oligo-recurrent PCA in Ga68- or F18-PSMA-PET/CT treated with 1-3 fraction robotic SBRT. Results: 60 patients/172 metastases were treated in 95 treatment series with 43 patients receiving >1 SBRT course. Median FU was 22 months. bPFS/SBRT-FS/ADT-FS was 6/23/32 months at 89.7% local control and 6.5/1.1% acute/late grade 1 AE. High PSA-nadir, initial pN1-status and longer time to PSA-nadir were predictive for worse bPFS/SBRT-FS. Discussion: Metastasis-Directed-Therapy using ablative focal SBRT is effective in bridging the gap between the identification of early metastases and the initiation of palliative systemic therapy. It is a fast outpatient procedure yielding high rates of local control, free of significant toxicity and repeatable if necessary. ADT could be withheld for almost 3 years. Patients with predictors for worse outcome could be identified.