Adjuvant Radiation vs Observation and Salvage Radiation after Subtotal Resection of a WHO grade I Skull Base Meningioma: a propensity score-adjusted analysis

Introduction: Surgical resection of skull base meningiomas (SBM) is challenging due to their proximity to critical neurovascular structures, often necessitating subtotal resection (STR). Following STR of WHO grade I SBM, there is considerable debate on employing upfront adjuvant radiation (AR), or observing and using salvage radiation (SR) upon tumor progression. Traditional progression-free survival (PFS) metrics overlook the possible effectiveness of SR. Thus, a more nuanced metric is critical to evaluate these treatment paradigms.

Methods: Patients with STR of a WHO I SBM from 1995-2021 were included. PFS was used to assess the effectiveness of AR, observation alone, and SR, measured from last treatment date. Radiation failure-free survival (RFFS) was used to compare AR versus observation with SR, measured from date of surgery to failure of first radiation. Multivariable Cox regression, adjusted for propensity score (PS) and inverse probability treatment weighted (IPTW), was performed to account for potential biases.

Results: A total of 179 patients were included. 25 (14.0%) received AR. Among 154 patients who underwent observation, 64 of 90 (41.6%) patients with tumor progression received SR. Median follow-up time was 77.5 months. In the observation group, PFS at 3, 5, and 10 years after STR was 60.6%, 47.5%, and 26.8%, respectively. The PFS/RFFS at 3, 5, and 10 years after AR was 84.2%, 77.2%, and 77.2%, respectively. After SR, PFS at 3, 5, and 10 years was 96.0%, 85.0%, and 80.0%, respectively. Observation with SR, if needed, resulted in a RFFS at 3, 5, and 10 years after STR of 100%, 97.7%, and 92.8%, respectively. PS and IPTW Cox regression models demonstrated that observation with SR, if necessary, significantly prolonged RFFS (HR = 0.06, p = 0.013; HR 0.08, p = 0.026, respectively) compared to AR.

Conclusion : After STR of WHO I SBM, most patients experience tumor progression. This analysis suggests that observation with salvage radiation can achieve longer radiation-failure free survival, potentially avoiding radiation or delaying radiation during the recovery period. However, close follow-up is necessary to avoid compression requiring re-operation.