Outcomes of Sterotactic Body Radiotherapy (SBRT) for Pelvic Lymph Node Recurrences after Adjuvant or Primary Radiotherapy for Prostate Cancer.

Background: There is a paucity of data on the management of recurrent lymph nodes after primary or adjuvant radiotherapy (RT) for prostate cancer (PCa). In this study, we report our tertiary cancer center experience with stereotactic body radiotherapy (SBRT) for the management of pelvic lymph node recurrences after adjuvant or primary RT for PCa. Materials and Methods: Patients who underwent SBRT for pelvic lymph node metastases from PCa between 2013 and 2019 were retrospectively assessed for local control (LC), androgen deprivation treatment-free survival (ADT-FS), and toxicity outcomes. The primary endpoint was LC and ADT-FS. The secondary endpoint was late treatment toxicity. Results: Twenty-two lesions of 18 patients receiving SBRT for pelvic lymph node recurrences for PCa between February 2013 and March 2019 were evaluated. At a median follow-up duration of 29.5 months (range: 9-54 months), LC was 95.5% vs. 90.2% at 1 and 2 years, respectively. Ten patients received palliative ADT following SBRT after a median period of 14.5 months (range: 6-31 months). ADT-FS was 72.2% and 54.3% at 1 and 2 years, respectively. Comparative analysis of biologically effective dose (BED) values revealed that higher BED10 values were associated with higher ADT-FS (P = 0.008). ADT-FS was 55.6% and 88.9% for BED10 <50 Gy and for BED10 >50 Gy, respectively (P = 0.008). Assessment of late toxicity outcomes revealed that the most common toxicity was urinary toxicity and fatigue; however, no patient had >= grade 3 toxicity. Conclusion: Our tertiary cancer center experience confirms the safety and efficacy of SBRT for the management of pelvic lymph node recurrences from PCa.