Exploring the Role of Radiosurgery for Atypical Meningiomas: Addressing Suboptimal Local Control in High-Risk Patients.

Purpose: Despite recent advancements in the treatment of atypical meningioma, control rates in high-risk patients continue to be suboptimal. Stereotactic radiosurgery (SRS) offers the ability to achieve improved local control (LC) with a low toxicity profile. However, available data are limited. We aimed to conduct a comprehensive review of a consecutive cohort of patients diagnosed with high-risk atypical meningioma who underwent SRS, either as a single-fraction SRS or in the hypofractionated SRS (hf-SRS), and evaluate the LC rates (LCR) with a specific emphasis on patterns of treatment failure. Methods and Materials: We identified consecutive patients diagnosed with high-risk World Health Organization grade 2 meningioma treated with SRS at a single institution between 2014 and 2021. High-risk meningioma was defined as a residual disease or recurrence after initial gross total resection. Follow-up data were analyzed to evaluate LCRs and patterns of treatment failure. We defined local failure as tumor recurrence wthin the prescription isodose line, marginal failure as recurrence within 5 mm but outside the prescription isodose line, and distant/regional failure as recurrence beyond 5 mm of the prescription isodose line but within 2 cm of the surgical cavity. Results: We identified 45 pathologically confirmed atypical meningiomas in 25 patients. Thirty-three tumors underwent single-fraction SRS, and 12 tumors received hf-SRS. The median follow-up was 36 months (range, 2-86 months). The 3-year LCR was 84.6%, and overall survival was 96.0%. Four patients with a total of 7 tumors experienced treatment failure. Failures were either local (3 patients and 3 lesions) or marginal (3 patients and 4 lesions). Patients treated with hf-SRS did not exhibit local, marginal, or distant failures. Conclusions: Our institutional data on atypical patients with meningioma treated with radiosurgery compare favorably to existing literature using fractionated radiation therapy. SRS offers a promising strategy to improve LC in this patient population, and the occurrence of marginal failure plays a role in creating clinical target volume margins.