Stereotactic Body Radiotherapy (SBRT) for Spinal Metastases: Who Will Benefit the Most from SBRT?

The purpose of this study was to evaluate local control and survival in patients with spinal metastases who were treated with stereotactic body radiotherapy (SBRT) using a CyberKnife, with or without a prior history of irradiation, and to identify prognostic factors predicting them. Between August 2008 and November 2012, 59 spinal metastatic lesions in 39 patients were treated with SBRT. Fourteen lesions (23.7%) were re-irradiated to treat recurrence after prior radiotherapy. Patients were treated with a median radiation dose of 27 Gy (range, 18-35 Gy) in a median of three fractions (range, one to five) using the CyberKnife Xsight Spine tracking system. Median planning target volume of the 59 spinal metastatic lesions was 37.4 cm(3) (range, 0.9-301.4 cm(3)). Radiation was prescribed to the median 80% isodose line that encompassed at least 90% of the tumor volume. The revised Tokuhashi scoring system and the Tomita scoring system were adopted to predict survival of patients. Local progression was defined as tumor progression by imaging, or if other therapy such as surgery or re-irradiation was given after SBRT, as salvage treatment. The median follow-up period was 7.4 months (range, 1.1-42.5 months). Four of 59 (6.8%) lesions experienced local progression, and all of them occurred within 1-year. Two of four local progressions occurred in re-irradiated tumors, which received 21 Gy in three fractions. With respect to treatment site-specific survival (TSS), better performance status and no visceral metastases were associated with a superior outcome (p = 0.011 and p = .001, respectively). With respect to overall survival (OS), better performance status was marginally related to superior outcome (p = 0.096). The revised Tokuhashi scoring system and the Tomita scoring system predicted OS and TSS in patients treated with SBRT. Two patients developed vertebral compression fractures at 1.2 and 1.4 months after SBRT with no evidence of tumor progression. There was no radiation-induced myelopathy. SBRT with a CyberKnife is a safe and effective treatment modality to achieve local control in spinal metastases patients, including those with a previous history of conventional RT. SBRT should be considered for those patients with a relatively indolent primary tumor, good performance status, and no visceral metastases. Survival of these patients can potentially be prolonged by long-term control of spinal metastases.