Spine Stereotactic Body Radiotherapy for Prostate Cancer Metastases and the Impact of Hormone Sensitivity Status on Local Control.

Abstract

Stereotactic body radiotherapy (SBRT) is used to deliver ablative dose of radiation to spinal metastases. To report the first dedicated series of spine SBRT specific to prostate cancer (PCa) metastases with outcomes reported according to hormone sensitivity status. A prospective database was reviewed identifying patients with PCa treated with spine SBRT. This included those with hormone-sensitive PCa (HSPC) and castrate-resistant PCa (CRPC). The primary end point was MRI-based local control (LC). A total of 183 spine segments in 93 patients were identified; 146 segments had no prior radiation and 37 had been previously radiated; 27 segments were postoperative. The median follow-up was 31 months. At the time of SBRT, 50 patients had HSPC and the remaining 43 had CRPC. The most common fractionation scheme was 24-28 Gy in 2 SBRT fractions (76%). LC rates at 1 and 2 years were 99% and 95% and 94% and 78% for the HSPC and CRPC cohorts, respectively. For patients treated with de novo SBRT, a higher risk of local failure was observed in patients with CRPC (P = .0425). The 1-year and 2-year overall survival rates were significantly longer at 98% and 95% in the HSPC cohort compared with 79% and 65% in the CRPC cohort (P = .0005). The cumulative risk of vertebral compression fracture at 2 years was 10%. Favorable LC rates were observed after spine SBRT for PCa metastases; strategies to improve long-term LC in patients with CRPC require further investigation.