Patterns of Failure After Postoperative Radiotherapy for WHO Grade 2-3 Meningiomas: A Single-Institution Experience

Background/Objectives: World Health Organization (WHO) Grade 2-3 meningiomas have high recurrence rates despite postoperative radiotherapy. This study aimed to characterize patterns of failure and clinical outcomes after postoperative external beam radiotherapy. Methods: We retrospectively analyzed 10 patients with WHO Grade 2 (n = 6) or Grade 3 (n = 4) meningiomas treated at a single institution between January 2017 and May 2024. Nine patients underwent gross total resection. Radiotherapy was delivered using three-dimensional conformal radiotherapy (n = 6) or intensity-modulated radiotherapy (n = 4), with a median dose of 60 Gy in 30 fractions. Recurrence patterns were assessed relative to the high-dose region. Results: The 1- and 3-year overall survival rates were 90% (95% CI, 47-99%) and 79% (95% CI, 38-94%), respectively; corresponding local control rates were 70% (95% CI, 33-89%) and 39% (95% CI, 7-71%), respectively. Recurrence occurred in six patients, predominantly within the high-dose region. Acute toxicities were limited to Grade 1 radiation dermatitis. During follow-up, Grade 3 seizures occurred in three patients, and worsening of pre-existing Grade 2 paresis occurred in four patients. Two seizure events and two cases of worsening paresis were considered more likely related to recurrent or progressive disease, whereas attribution of the remaining neurological events to radiotherapy was uncertain. Conclusions: Despite postoperative radiotherapy, local control remained limited in this small, single-institution series, with a predominance of in-field recurrence. This pattern raises the possibility that tumor biological factors, in addition to technical and treatment-related factors, may contribute to treatment failure in WHO Grade 2-3 meningiomas. These findings are exploratory and warrant validation in larger studies incorporating molecular stratification and standardized treatment approaches.