1178 Outcomes of Salvage Radiation Therapy for Recurrent World Health Organization Grade 1 Meningiomas

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INTRODUCTION: Salvage radiation in the form of intensity-modulated radiotherapy and Gamma Knife stereotactic radiosurgery are mainstay treatments for recurrent world health organization (WHO) grade 1 meningiomas. However, little is known on the optimal radiation modality (IMRT or SRS) to treat recurrent WHO grade I meningiomas. METHODS: This was a single-institution retrospective study of patients treated with IMRT or Gamma Knife SRS for recurrent WHO grade I meningiomas between 1996 and 2024. Our analysis included one hundred thirty-three salvage operations with 28 recurrences/progressions. One hundred twenty-eight salvage radiation treatments were performed on recurrent tumors never treated with prior radiation (radiation-naïve’ cohort), Thirty salvage treatments were performed on meningiomas that either received adjuvant radiation or salvage re-operation (re-treatment’ cohort). RESULTS: In the ‘radiation-naïve’ cohort, 5- and 10-year PFS for IMRT and SRS were 72.5%, 59.4% and 81.3%, 65.6% respective (p = 0.41). The median months till progression/recurrence for patients treated with IMRT or SRS was comparable between the two modalities (21.5 [13.9-51.6] months vs 40.2 [23.9-54.8] months; p = 0.41). Significantly larger radiation tumor volumes were observed in the IMRT cohort compared to SRS (16.7 [9.7-34.0]) vs 3.9 [1.6-6.8]; p < 0.001). The 5- and 10-year PFS was significantly shorter in the retreatment cohort compared to the radiation-naïve cohort (p < 0.0001). CONCLUSIONS: In patients with recurrent WHO grade I meningiomas who had not received prior radiation, salvage IMRT and SRS demonstrated comparable 5- and 10-year progression-free survival, despite differences in tumor volume treated. However, outcomes were significantly poorer in the retreatment cohort, underscoring the importance of initial treatment strategy. These findings suggest that both IMRT and SRS are viable salvage options in radiation-naïve patients and highlight the need for further prospective studies to optimize individualized radiation approaches and improve long-term tumor control.

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