Recurrence pattern of stereotactic body radiotherapy in oligometastatic prostate cancer: a multi-institutional analysis.

Purpose: For patients with oligometastatic/oligorecurrent/oligoprogressive lymph node metastases from PCa, metastases-directed therapy is an emerging strategy. The aim of this retrospective study was to evaluate the oncological outcome and pattern of recurrence in patients treated with stereotactic body radiation therapy (SBRT) to lymph node metastases.
Methods: In this multi-institutional analysis, patients with a maximum of five lymph node metastases from PCa treated with SBRT were included. Primary endpoints of the analysis were local control (LC), out-of-field nodal progression-free survival (NPFS), overall progression-free survival (PFS), and overall survival (OS).
Results: 109 patients and 155 lymph node metastases were evaluated. Patients' median age was 70.8 years (range 51-84) and median PSA before SBRT was 1.88 ng/ml (range 0.3-45.5 ng/ml). The dose delivered to the target ranged from 25 to 48 Gy in 4-7 fractions; median BED _{1.5   Gy} was 198 Gy (range 108.3-432 Gy). With a median follow-up of 16 months, LC rates at 1 and 3 years were 93% and 86%, respectively. In-field progression of disease was observed in 11 (7%) lesions. One- and 3‑year NPFS was 59% and 29%, and median NPFS was 15 months. Rates of OS at 1 and 3 years were 100% and 95%. The median time to administration of a systemic treatment after SBRT was 7.8 months (1.7-54.8).
Conclusion: SBRT is an effective and well-tolerated treatment option in the management of lymph node metastases from PCa. Prospective trials are necessary to better select patients who benefit most from this ablative focal treatment and better define the recurrence patterns.