Clinical Outcomes and Patterns of Failure in Patients with High-Risk Atypical Meningioma Treated with Single Fraction vs. Hypofractionated Gamma Knife Radiosurgery

Abstract

The recently completed RTOG 0539 supports fractionated radiation therapy for patients categorized as having intermediate (3 yr PFS 93.8%) or high-risk (3 yr LC 68.9%) meningiomas. Stereotactic radiosurgery (SRS) has not been widely established in the treatment of WHO grade 2 atypical meningiomas given concern that there is a greater risk of microscopic infiltration and therefore requires larger margins than safely achievable with SRS. We look to review a consecutive cohort of patients at our institution who have been diagnosed with atypical meningioma treated with either single fraction Gamma Knife SRS (GK-sfSRS) or hypofractionated Gamma Knife SRS (GK-hfSRS). We review both control rates and patterns of failure. Patients diagnosed with intermediate or high-risk WHO grade 2 meningioma per RTOG 0539 classification, without a history of prior radiation (RT) and treated with either GK-sfSRS or GK-hfSRS between 2014 to 2021 at our institution, were included. Patient charts were reviewed, and follow-up data were analyzed for local control (LC) and failure patterns. Local failure was defined as tumor recurrence within the prescription isodose line, marginal was ≤5 mm outside the prescription isodose line, and distant was >5 mm outside of the prescription isodose line Primary outcome was LC, and secondary outcomes were overall survival (OS) and progression free survival (PFS). We identified 47 pathologically confirmed WHO grade 2 meningiomas in 27 patients. 33 lesions were treated with GK-sfSRS and 14 lesions with GK-hfSRS. 6 lesions were intermediate risk, and 41 were high-risk per RTOG 0539. With a median follow up of 36 months (range 2-86 mo), the 3yr LC was 82.7%, PFS was 83.1%, and OS was 96.3%. A total of 4 patients with 8 lesions failed treatment - all with high-risk disease. All failures were local (4) or marginal (4). The 4 local failures were all from a single patient with 4 distinct meningiomas that were treated with GK-sfSRS without surgical resection. The 4 marginal failures were all in patients treated with GK-sfSRS. There were no failures in patients treated with GK-hfSRS. Our institutional data for patients with atypical meningiomas treated with radiosurgical techniques compare favorably to the patients treated with EBRT in RTOG 0539, though longer follow-up is needed to confirm these findings. Outside of one patient, no patients developed recurrence within the prescription volume. There were 4 tumors with marginal failures, suggesting that additional dural margins than what were prescribed may be meaningful. At our institution, we are increasingly moving to hypofractionated radiosurgery with 5 mm of dural margin when using radiosurgical techniques for high-risk atypical meningioma. However, longer term follow-up is needed to validate the use of radiosurgical techniques in atypical meningioma.