Stereotactic Body Radiation Therapy (SBRT/SABR) for Oligometastatic Prostate Cancer: Metastasis Control, Progression-Free Survival, Survival, and Toxicity

Abstract

Purpose: To evaluate clinical outcomes after stereotactic body radiation therapy (SBRT), also termed stereotactic ablative radiotherapy (SABR), for oligometastatic prostate cancer (PCa) and to identify factors associated with local failure of treated metastatic lesions. Methods and Materials: We retrospectively reviewed records of patients treated with SBRT for oligometastatic PCa. Metastasis control (MC; local control of the treated lesion), biochemical progression-free survival, distant progression-free survival, and overall survival were estimated using the Kaplan-Meier method. Results: Sixty-six men with 81 metastatic PCa lesions were included; 50 lesions were castrate-resistant. Metastatic sites were bone (n=74), lymph nodes (n=6), and liver (n=1). SBRT was delivered in 1 fraction to 71 lesions (88%) at a median dose of 16 Gy (range, 16-24 Gy). Other lesions received 30 Gy in 3 fractions (n=6) or 50 Gy in 5 fractions (n=4). Median follow-up was 16 months (range, 3-49 months). Estimated MC at 2 years was 82%. Biochemical progression-free survival, distant progression-free survival, and overall survival were 54%, 45%, and 83%, respectively. On multivariate analysis, SBRT dose was the only variable significantly associated with MC: lesions treated with 16 Gy had 58% MC, whereas lesions treated with ≥18 Gy had 95% MC at 2 years (P<.001). At 2 years, MC for lesions treated with 18 Gy (n=21) was 88%. No local failure occurred after ≥18 Gy in a single fraction or after any multifraction regimen. Grade 1 pain flare occurred in 6 patients (9%), and grade 2 pain flare occurred in 2 patients (3%). No grade 2 or greater late toxicities were reported. Conclusions: SBRT for oligometastatic prostate cancer provided optimal metastasis control and acceptable toxicity with doses ≥18 Gy. Biochemical progression-free survival was 54% at 16 months with SBRT included in the treatment regimen. SBRT should be considered for patients with castration-refractory oligometastatic prostate cancer who have limited systemic therapy options.