Radiotherapy for WHO grade 1 and 2 Intracranial Meningiomas - A Retrospective Analysis of Efficacy.

Purpose: To evaluate the efficacy of radiotherapy (RT) for WHO grade 1 and 2 intracranial meningiomas, focusing on the impact of post-surgical tumor volume on treatment outcomes.

Methods: Adult patients (≥18 years) with WHO grade 1 or 2 intracranial meningiomas who received RT between January 1, 2019, and April 1, 2022, were identified. Exclusion criteria encompassed known extracranial tumors, preoperative radio- or chemotherapy, and insufficient RT modality data. Patients were treated according to the international guidelines. Tumor recurrence was identified on MRI with a follow-up period until April 2024. Kaplan-Meier estimates for progression-free survival (PFS) calculations and Cox proportional hazard models were performed to evaluate the impact of tumor volume and other covariates on PFS.

Results: Among 113 patients with intracranial meningiomas who received RT, 103 met the inclusion criteria. Of these, 84.5% received photon-based and 15.5% proton-based treatment. The cohort was predominantly female (72.8%) with a mean age of 59 years. The 2-year and 5-year PFS rates were 95.6% and 90% for grade 1 tumors, respectively, and 83.3% for grade 2 tumors. Tumors >21 cm post-surgical pre-RT had a significantly higher risk of progression (HR = 4.35, p = 0.006).

Conclusions: Tumor volume was identified as a key prognostic factor for PFS in WHO grade 1 and 2 intracranial meningiomas treated with RT. A critical post-surgical volume threshold of 21 cm significantly influences 2-year and 5-year PFS rates, with patients exceeding this threshold experiencing a 335% increase in risk of progression.