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RADT-41. ASSESSING THE ROLE OF ADJUVANT RADIATION THERAPY AND RISK FACTORS FOR RECURRENCE FOLLOWING GROSS TOTAL RESECTION OF ATYPICAL MENINGIOMAS


 While meningiomas are commonly benign brain tumors, as many as 30% may be classified as atypical, or WHO Grade 2. Patients are at risk of recurrence following resection and often are prescribed adjuvant radiation therapy (RT)-although most data on this treatment is retrospective and has shown mixed RESULTS: In this study we assessed the influence of adjuvant RT following gross total resection (GTR) in patients with newly diagnosed atypical meningiomas at our institution and sought to determine predictors of tumor recurrence. All patients who underwent GTR (Simpson Grade I and II) at their index operation from 1994-2014 were retrospectively reviewed. Patients then either underwent observation or adjuvant RT (Intensity-Modulated Radiation Therapy (IMRT) or stereotactic radiosurgery (SRS)). A total of 145 patients had documented GTR at the time of initial resection, including 88 females (61%) and 57 males (39%), with a mean age of 58 +/- 15.7 years. 118 patients were followed with observation after surgery while 27 (18.6%) patients received adjuvant RT prior to known recurrence (IMRT for 15 patients (55.5%) and SRS in 12 patients (44.4%)). Patients receiving adjuvant RT had significantly larger tumors, as well as a higher incidence of spontaneous necrosis and small cell phenotype on histopathology. Overall 5-year PFS in our cohort was 71.6% (CI 60.6%-84.7%) and was unchanged by adjuvant RT (p = 0.52). 23 patients (15.8%) had a recurrence with a mean follow up of 42.9 months (17.1-53.5 months). Male gender (HR=1.02, p=0.019), tumor size (HR=1.17, p= 0.002) and MIB-1 > 4 (HR=8.50, p=0.04) were associated with increased recurrence risk. There was no association between radiation type (SRS vs. IMRT) and risk of recurrence (p= 0.154). In our patients, adjuvant RT following GTR of atypical meningiomas did not improve PFS. Risk factors for recurrence included male gender, larger tumor size, and MIB-1 > 4.