Stereotactic Body Radiotherapy for the Management of Spinal Metastasis from Renal Cell Carcinoma

Renal cell carcinoma (RCC) metastases are radioresistant and may require higher doses of radiation to achieve durable local tumor control. Here, we report the outcomes and toxicity from stereotactic body radiotherapy (SBRT) for RCC metastasis of the spine. Between 2008 and 2019, 75 patients with 103 RCC metastases to the spine were treated with SBRT. Clinical and radiographic outcomes were collected retrospectively. Radiographic local control (LC) was determined by SPINO consensus criteria with local failure defined as evidence of disease progression at the site of SBRT with positron emission tomography or magnetic resonance. Overall survival (OS) and LC were measured by Kaplan-Meier method. Acute and late adverse events (AE) were measured by CTCAE v5.0. The median follow-up was 17.6 months. OS at 1, 2, and 5 years was 58%, 50%, and 20%. Metastatic sites were treated with SBRT alone (56%), surgery and SBRT (29%), SBRT and percutaneous radiofrequency or cryoablation (13%) and surgery, SBRT, and percutaneous ablation (2.0%). 68% of patients who underwent surgery were Bilsky 1 or higher. Most patients (69%) with no prior RT received a single fraction of 24 Gy (R, 16-24 Gy). A total of 30% of patients had prior spinal RT and most frequently received 3-fraction SBRT with a median dose of 30 Gy (R, 27-39 Gy). Radiographic follow up was adequate to evaluate local control at 73 spinal sites. 22 local failures were observed. The 1, 2, and 5 year LC was 77.7%, 59.9%, and 56.7%. LC was no different between single or multimodality treatment (p = 0.15) or SBRT dose or fractionation (p = 0.92). The locations of the 22 local failures were vertebral body (10), posterior elements (5), epidural space (3), para-spinal soft tissue (3), and neuroforamina (1). Acutely, 32 patients (33%) experienced pain flare with 3 requiring hospitalization for pain management. Of 78 analyzable patients, 19 vertebral body fractures (VBF) were observed (24.3%). There were no acute or late grade 4 or 5 AEs. Late grade 3 AE occurred in 7 patients who had prior surgery (n = 6) or RT (n = 5). This included 3 patients with unilateral peripheral neuropathy (4.8%), 2 postop wound complications (3.2%), and 1 pedicle fracture (1.6%). SBRT for the treatment of RCC spinal metastases provides durable local tumor control with an acceptable rate of acute AEs and VBF. In contrast to previous reports, local failure was most common in osseous elements as opposed to epidural space, possibly related to surgical debulking and post-SBRT percutaneous ablation in patients with epidural involvement.