Stereotactic Radiosurgery (SRS) for Spinal Metastatic Disease: Outcomes From the RSSearch Patient Registry

Abstract

While increasing evidence supports the use of stereotactic radiosurgery (SRS) for oligometastatic spinal disease, there is mixed prospective evidence on its effectiveness for pain compared to conventional radiation therapy and limited evidence to guide optimal patient selection in the setting of asymptomatic disease.A prospectively maintained multi-institutional registry was queried for patients with spinal metastatic disease treated with single-fraction SRS (SF-SRS) or fractionated SRS (MF-SRS). Potential predictive factors of local control (LC) and overall survival (OS) were evaluated. Pre-treatment and post-treatment visual analog scores (VAS) were analyzed to examine both initial and durable pain responses in addition to complete response (CR) rates with patients with VAS scores < 3 excluded from analysis. Logistic regression was utilized to examine potential correlations between pain response, fractionation, and prescription dose.Four-hundred and sixty-eight patients were identified with 514 lesions treated with SRS. Median follow-up was 8.8 months (range: 0.4-89.7). Median patient age was 65 years, median KPS was 80%, and the median gross tumor volume (GTV) was 30.6cc. The median pain score of patients initially with symptoms was 6 (range: 3-10). The median biologically effective dose (BED10) and dose/fraction were 50.4 Gy10 and 10 Gy, respectively, with 99 patients treated with SF-SRS. Common primary locations included the lung (25.4%), breast (18.1%), kidney (10.5%), and prostate (9.2%). One- and 2-year OS rates were 53.4% and 33.6%, respectively. Utilizing KPS, age, and primary site (lung and/or non-breast), 1-year OS rates were 76.1%, 59.1%, 54.9%, 37.2%, and 23.5%, for patients with 0-4 of these factors, respectively (P < 0.0001). One- and 2-year LC rates were 79.9% and 73.6%, respectively, with no difference in LC between SF- and MF-SRS. Eighty-six patients (82.7%) had an initial decline in pain scores with a median decline of 3.5 and a CR rate of 47.1% (SF-SRS: 47.6% vs. MF-SRS: 47.0%). At last follow-up, 65 patients (62.5%) had a durable decline in pain scores with a median decline in pain score of 2 and a CR rate of 20.2% (SF-SRS: 28.6% vs. MF-SRS: 18.2%; P = 0.29). No significant difference in either initial (P = 0.30) or durable pain scores of < 3 (P = 0.31) or < 4 (P = 0.56) was found between SF-SRS vs. MF-SRS.Patients with spinal metastases treated with SRS had encouraging palliative responses. Greater than 80% of patients had an initial pain response and close to 50% an initial CR with durable pain response achieved for roughly 60% of patients. Performance status, age, and primary histology (lung and or/breast) are prognostic factors to consider when determining suitability for SRS in the absence of pain.