Local Control Assessment of Spine Metastases after Post-operative Stereotactic Radiosurgery Following Limited Versus Extensive Spine Surgery: A Retrospective Review

Abstract

Adjuvant conventional radiation therapy has been the historical standard after surgical decompression and stabilization for spinal metastases. In the era of modern, more advanced radiation techniques, however, stereotactic radiosurgery (SRS) is increasingly being utilized in the post-operative setting for more durable local control, primarily in the setting of more radioresistant histologies such as renal cell carcinoma. The objective of our study is to review our institutional experience using SRS in the post-operative setting, following either complete vertebrectomy (VT) or more limited surgery, for spinal metastases and to assess local tumor control and survival. We retrospectively identified 47 patients treated with spinal surgery followed by SRS between 2010 and 2016. Patients with significant delays to SRS (>2 months) and inadequate radiographic follow-up (<2 months) were excluded. Of those 47 patients, 20 patients with 21 tumors were eligible for analysis. The median follow-up was 9.2 months. Eight tumors (38%) were treated with complete VT and 13 tumors (62%) were treated with either a partial VT or laminectomy for cord decompression. Post-operative SRS doses ranged from 15 to 27Gy in 1 to 5 fractions. Tumor histologies, time to local progression after SRS using serial MRI imaging, time to recurrence requiring intervention, and time from completion of SRS to death were evaluated. Descriptive statistics and log rank tests were used to evaluate these end points. The majority of tumors were renal cell carcinoma (N=9, 43%). Post-operatively, most tumors were treated with either 27Gy in 3 fractions (N=13, 62%) or 18Gy in 1 fraction (N=4, 19%). Four tumors (19%) showed evidence of radiographic progression by the end of the study - 1 patient in the VT group and 3 patients in the sub-VT group. None of the patients with progression required intervention. Radiographic progression-free survival was not significantly different between the two groups (46.7 vs. 19.6 months, p=0.677). Eight patients (40%) of 20 patients died during this study. All deaths were attributable to systemic progression and not local failure. The mean overall survival after SRS was approximately 35 months (range 5.2-55 months). This was not statistically different between those treated with VT versus those treated with more limited surgeries (36 vs. 23.1 months, p = 0.756). Extent of surgery did not appear to significantly impact time to radiographic progression, intervention-free survival or survival after SRS, however we recognize that this may be due to low sample size. Although we are still waiting for the data to mature and are continuing to collect data, this is one of the largest series to date looking specifically at the extent of surgery prior to post-operative SRS and how it relates to local control outcomes using radiographic follow-up in the management of spinal metastases.