Cytoreduction and Long-Term Outcome After Single-Fraction or Hypofractionated Stereotactic Radiosurgery for Atypical Meningiomas: Ten-Year Experience

Objectives: : This study is to evaluate the association between post-radiosurgery cytoreduction and long-term response after single-fraction (sfSRS) or hypofractionated stereotactic radiosurgery (hfSRS) for atypical meningiomas.

Methods: : Patients diagnosed with atypical meningioma (WHO grade II) treated with either sfSRS or hfSRS between April 2014 to April 2024 at a single institution were included. History of prior brain radiation likely inducing current atypical meningioma was recorded. Meningioma size was measured on MRIs of radiosurgery and 6 months after radiosurgery to calculate percentage of size reduction. Long-term response was evaluated per meningioma RANO criteria. Failure patterns were categorized into local failure (within the prescription isodose line), marginal failure (≤5 mm outside the prescription isodose line), and distant relapse (>5 mm outside of the prescription isodose line).

Results: : Among 64 patients with 123 atypical meningiomas, 46 patients with 89 lesions treated with either sfSRS (62%) and hfSRS (38%) were prospectively followed over 1 year. Median progression free survival (PFS) was 31 months (range 4 - 105 months). The 6-month size product decreased by 4%. Size product reduction was more pronounced in hfSRS vs. sfSRS (14% vs. -3%, p=0.02). While distant relapse was same (17% vs. 20%, p=1.00), local and marginal failures differed between hfSRS vs. sfSRS (6% vs. 20%, 0 vs. 18%, p=0.07 and 0.01 respectively). History of prior brain radiation (n=32) was associated with distant relapse and overall progression (p < 0.0001 and 0.0006) but not associated with local and marginal failures (p=0.41 and 0.78). Three-year PFS was significant different in patients with or without history of prior brain radiation (42% vs. 73%, p=0.004). Logistic regression analyses revealed a strong correlation between 6-month size reduction and long-term response (HR=76.8, p=0.0005).

Conclusion(s):: Post-SRS cytoreduction may be a robust tool to predict long-term response. While mask-based hypofractionated SRS provided superior loco-marginal control, there is unmet need to reduce distant relapse in RT-induced atypical meningiomas.