2651 - Long-Term Outcomes Following Stereotactic Radiosurgery and Radiotherapy for Benign Skull Base Meningioma

N. J. Zhou¹, A. Beighley¹, Y. Kesbeh¹, J. Rahimian², A. Wong², F. Torres², A. Rajamohan², J. Han³, K. Lodin², M. R. Girvigian², and O. Bhattasali²; ¹Kaiser Permanente Los Angeles Medical Center, Los Angeles, CA, ²Southern California Permanente Medical Group, Los Angeles, CA, ³Southern California Permanente Medical Group, Anaheim, CA

Purpose/Objective(s): Although multiple prior studies have demonstrated favorable initial local control (LC) outcomes following stereotactic radiotherapy for benign intracranial meningioma, there is a paucity of long-term data. Due to the indolent nature of this disease, late progression events may occur. The purpose of this analysis is to evaluate treatment outcomes for skull base meningioma at least ten years following stereotactic radiosurgery or radiotherapy to better understand long-term disease control. Materials/

Methods: A retrospective chart review was performed within an integrated health care system of 229 patients with 237 histologically-proven WHO grade I or radiographically-defined benign skull base meningioma treated with single-fraction stereotactic radiosurgery (SRS) (n=60), fractionated SRS (FSRS) over 5 fractions (n=31), or conventionally fractionated stereotactic radiotherapy (FSRT) (n=146) between January 2003 and December 2013. Patients without a local failure event were required to have a minimum of 10 years of follow-up for inclusion. Patients were treated with radiation either in the definitive (n=179) or postoperative (n=58) settings. LC outcomes were estimated by the Kaplan-Meier method. Multivariate analyses were performed using Cox proportional hazards models.
Results: Median follow-up per lesion was 13.7 years (range: 10.0-20.4). Median patient age was 58 years (range: 24-84). Patients were predominantly female (79.5%). Median tumor volume was 5.65 cm³ (range: 0.14-99.9). Most lesions treated in the postoperative setting had undergone subtotal resection (68.4%). Median time between surgical resection and radiotherapy was 1.3 years (range: 0.2-24.4). LC rates at 10/15/20 years were 92.8%/89.6%/86.2%. Median time to local failure was 8.2 years (range: 0.4-17.1). Of the 29 local failures observed, 25 (86.2%) and 7 (24.1%) occurred more than five years and ten years post-radiotherapy, respectively. On multivariate analysis, both male sex (HR=2.42 (95% CI: 1.04-5.63), p=0.04) and larger tumor volume (HR=1.03 (95% CI: 1.01-1.05), p=0.002) were associated with inferior LC. Age, prior surgical resection, meningiomatosis, and radiotherapy technique were not associated with LC. Dose escalation =1250 cGy for SRS (p=0.13) or =5040 cGy for FSRT (p=0.14) was not associated with improved LC. Failures were managed with observation (n=16), resection (n=8), re-irradiation (n=4), or medical therapy (n=1). Two patients had WHO grade II disease on salvage resection. Four deaths were attributed to progression of disease.
Conclusion: In patients with benign skull base meningioma, treatment with stereotactic radiosurgery or radiotherapy results in durable LC at long-term follow-up. Almost one-fourth of treatment failures occurred more than ten years after radiotherapy, suggesting the importance of long-term imaging surveillance. These results may inform prognosis and follow-up protocols.