Volumetric regression of meningiomas following SRS and hFSRT: insights from long-term analysis

Background: Meningiomas are the most common primary brain tumors in adults, typically managed with surgery, stereotactic radiosurgery (SRS), or hypofractionated stereotactic radiotherapy (hFSRT). While local control rates are high, volumetric regression dynamics and radiobiological parameters remain underexplored. This study evaluates meningioma regression after SRS and hFSRT and estimates the α/β ratio to refine radiotherapy strategies. Materials and methods: A retrospective analysis included 150 patients with intracranial meningiomas treated between 2010–2021. Volumetric assessment was performed for 62 lesions (1–10 cm³) treated with SRS (1 × 14 Gy) or hFSRT (3×7 Gy, 5×5 Gy, 5×6 Gy). Tumor volumes were measured pre-treatment and during follow-up using 3D MRI reconstruction. Radiobiological modeling and α/β calculation employed linear-quadratic (LQ) and linear-quadratic-linear (LQ-L) models. Results: SRS achieved significantly faster regression, with tumors shrinking by 32.7% at 2 years and 67.4% at 4 years, compared with 15.3% and 31.7% for hFSRT (p = 0.003). The α/β ratio was calculated at 3.15 Gy [95% confidence interval (CI): 3.07–3.23], refining understanding of meningioma radiobiology. Local control reached 91.3%, with comparable outcomes for SRS (91.4%) and hFSRT (91.3%). Symptomatic complications included brain edema (7.9%) and radiation necrosis (2.6%). Conclusion: CyberKnife SRS and hFSRT are effective and safe for meningiomas, though SRS induces faster volumetric regression (19% vs. 9% annual reduction for hFSRT). The α/β ratio of 3.15 Gy provides novel radiobiological insight, supporting more personalized treatment strategies.