Brain parenchyma dose-volume predictors of toxicity following Gamma Knife radiosurgery for convexity, parasagittal, and falcine meningiomas.

Abstract

Introduction: This study evaluates the relationship between key dosimetric parameters and the risk of toxicity following Gamma Knife stereotactic radiosurgery (SRS) for convexity meningiomas, with a focus on refining brain parenchyma-specific dose-volume assessment. Traditionally, V ₁₂ - the volume of brain receiving at least 12 Gy - has included the entire intracranial volume, thus potentially overestimating the safe brain exposure. We hypothesized that contouring only the brain parenchyma adjacent to the tumor, excluding non-functional spaces such as cerebrospinal fluid, sulci, and vascular structures, provides a more accurate predictor of toxicity and may improve strategies to reduce symptomatic brain edema and radiation necrosis.

Methods: In this retrospective analysis, 85 convexity meningioma lesions in 68 patients treated with SRS between 2004 and 2020 were evaluated. Detailed dosimetric parameters, including V ₁₀-V ₁₅, tumor volume, and surface area, were extracted from GammaPlan. Adjacent brain parenchyma was contoured as an organ at risk, excluding sulci and vascular structures. Statistical analyses, including receiver operating characteristic curve determination, logistic regression, and probability distribution analysis, were employed to identify dosimetric thresholds predictive of radiation-induced changes (RIC) and to compare outcomes across different prescription doses.

Results: Increased brain parenchyma V ₁₂ significantly correlated with higher RIC incidence. A parenchyma-specific V ₁₂ threshold of 2.65 cc optimally predicted both asymptomatic (sensitivity 82%, specificity 71%) and symptomatic RIC (sensitivity 85%, specificity 75%), a notably smaller volume than traditionally reported thresholds.

Conclusion: Our results support adopting brain parenchyma-specific V ₁₂ as a refined predictive dosimetric metric for assessing radiation-induced toxicity in convexity meningiomas. Implementing this refined, parenchyma-specific assessment can enhance safety in SRS, guide individualized treatment decisions, and serve as a practical reference for planning - particularly in eloquent cortical regions where minimizing high-dose brain exposure is critical.