Augmenting fractionated radiotherapy with a stereotactic radiosurgery boost for grade 2 meningioma and ependymoma

Introduction: Opportunity exists for improved local control rates of grade 2 meningiomas and ependymomas that recur despite maximal surgical resection and adjuvant fractionated radiotherapy, with historical 3-year progression free survival (PFS) rates ranging from 56-58%. We describe a dose escalation strategy of increasing the total tumor radiation dose by adding a stereotactic radiosurgery boost to fractionated radiotherapy.

Methods: A single institution retrospective cohort of patients from 2009-2023 with grade 2 meningioma or ependymoma treated with surgical resection, fractionated radiotherapy, and stereotactic radiosurgery (SRS) boost to the gross disease were evaluated for baseline characteristics, local disease control, and adverse events (AE).

Results: Sixteen patients were included, including 13 (81%) meningioma patients and 3 (19%) ependymoma patients. Twelve patients (75%) underwent radiosurgery at initial diagnosis, while 4 patients (25%) were treated for recurrent disease. The median fractionated dose delivered was 54 Gy ± 1.8 IQR using 1.8 Gy in 25-31 fractions. For SRS, the median dose delivered was 8 Gy ± 3.5 IQR to the 50% isodose line in 1 fraction. The median cumulative biologically equivalent radiation dose in 2-Gy fractions (EQD2) was 67.52 Gy ± 13.6 IQR. Of the 16 total patients, 15 had follow-up available, with a median follow-up of 34 months (range, 5-67). Three-year PFS was 72%. Three patients (20%) had treatment failures, however, no failure occurred within the SRS volume, one was marginal within the fractionated volume, and two thirds occurred in patients treated for recurrent disease. Most patients experienced no or mild AEs, however, 3 patients (20%) experienced a high-grade (CTCAE v5.0 grade ≥ 3) AE including radiation necrosis, seizures, and cognitive decline.

Conclusion : Within the limitations of a small sample size, we found a 100% in-field success rate from an SRS boost to fractionated radiotherapy, suggesting this may be an effective treatment strategy in patients with grade 2 meningioma or ependymoma.