[Ga68]-Dotatate/mri-guided Fractionated Stereotactic Radiosurgery for Residual/Recurrent Atypical Meningiomas – Local Control and Salvage Requirements in a Single Institution Series

Purpose/Objective(s) The NCI-sponsored phase III NRG protocol BN-003 randomizing completely resected atypical meningiomas to observation or fractionated radiotherapy to the resection bed requires clinical equipoise to ethically randomize patients between the two arms. A radiographically complete resection, required for protocol eligibility, may be Simpson Grade 1, 2, or 3, which differ in excision completeness and thus in risk of recurrence. Meningiomas express high levels of somatostatin receptor 2A, which avidly binds [68Ga]-DOTATATE, a PET tracer that permits differentiation of postoperative scar tissue from residual/recurrent meningioma. We hypothesized that using [68Ga]-DOTATATE PET/MRI would permit the radiosurgical treatment of patients with atypical (WHO Grade 2) meningiomas not completely removed at surgery, thereby sparing normal brain high-dose irradiation and shortening treatment from six weeks to one. We prospectively accrued patients with residual/recurrent atypical meningiomas at our institution and subsequently investigated their local control (LC) and salvage requirements after treatment with fractionated stereotactic radiosurgery (fSRS) that incorporated [68Ga]-DOTATATE PET/MRI in the planning process. Materials/Methods We approached patients with pathologically confirmed atypical meningioma for an Institutional Review Board approved prospective trial of [68Ga]-DOTATATE PET/MRI imaging. fSRS (35 Gy in 5 fractions) was offered to patients with positive findings. 20 tumors in 19 patients were treated. Patients were scheduled for follow-up MRI and [Ga68]-DOTATATE PET scanning per protocol on an at least semi-annual basis. Not all patients have yet presented for follow-up imaging. LC duration was calculated from the first day of fSRS until the most recent MRI. No patients were lost to follow-up. Results 20 fSRS sessions were delivered, LC was achieved at fSRS sites in all patients. Median follow-up is 15.9 months (range: 0-35.7, SD 11.1). One patient progressed remote from the original site of disease and was managed with [Lu177]-DOTATATE and salvage SRS to a new nodular focus. Two patients had surgical bed recurrences, one of which was managed with salvage re-resection (now WHO Grade III), followed by fractionated radiotherapy; the other is pending salvage fSRS. Overall, 16/19 patients (84%) have experienced progression-free survival to date after [Ga68]-DOTATATE PET/MRI guided fSRS of residual/recurrent atypical meningioma. No unusual toxicities were reported by patients in follow-up, and no patients required treatment for radiation injury. Conclusion [Ga68]-DOTATATE PET/MRI can assist with radiation management of residual/recurrent atypical meningiomas through improving the ability to discern what volumes of tissue require aggressive focal treatment, and what volumes are at low risk and can be spared treatment. Further follow-up will help clarify the value of this approach.