# Optimal α/β Ratio for Biologically Effective Dose-Based Prediction of Radiation-Induced Peritumoral Brain Edema in Meningioma

## TL;DR

This study identifies an optimal α/β ratio of 14 for predicting radiation-induced brain swelling in meningioma patients, suggesting a biologically effective dose threshold of around 41 Gy to reduce complications.

## Contribution

The study introduces a refined radiobiological model using an α/β ratio of 14 for predicting peritumoral brain edema after meningioma radiotherapy.

## Key findings

- An α/β ratio of 14 provides the highest predictive accuracy for radiation-induced peritumoral brain edema.
- A biologically effective dose threshold of approximately 41 Gy is optimal for predicting PTBE in meningioma patients.
- Lowering prescribed doses below this threshold may reduce PTBE risk, especially in patients under 70 years old.

## Abstract

Peritumoral brain edema (PTBE) remains the most frequent complication following radiotherapy for intracranial meningiomas, yet a clinically reliable biologically effective dose (BED) threshold to predict this toxicity has not been defined. This study systematically evaluated a range of assumed α/β ratios to identify the most appropriate radiobiological model for predicting PTBE in convexity, parasagittal, and falcine meningiomas treated with primary LINAC-based radiotherapy. The analysis demonstrated that an α/β ratio of approximately 14 provides the highest predictive accuracy, corresponding to an optimal BED threshold of around 41 Gy. These results indicate that maintaining prescribed doses below this level may reduce the risk of radiation-induced PTBE, particularly in patients younger than 70 years. The findings propose a refined BED-based framework that could improve individualized dose planning and the radiobiological understanding of PTBE formation in meningioma radiotherapy.

Background: Peritumoral brain edema (PTBE) is the most frequent complication for intracranial meningiomas following radiotherapy, yet no clinically validated biologically effective dose (BED) threshold capable of reliably predicting PTBE has currently been established. Although conventional radiobiological models typically assume an α/β ratio of 2–4 for benign meningiomas, whether these values accurately reflect the dose–response characteristics underlying radiation-induced PTBE remains unclear. Methods: We analyzed 67 intact meningiomas in the convexity, parasagittal, or falcine regions treated with primary linear accelerator (LINAC)-based radiotherapy. The BED values were recalculated using α/β ratios ranging from 2 to 20, and receiver operating characteristic (ROC) analyses were performed to identify the optimal BED thresholds for predicting PTBE. The most informative α/β ratio was defined as the value yielding the highest Youden’s J statistic. Results: The ROC analyses showed that an assumed α/β ratio of 14 provided the highest discriminative accuracy for predicting PTBE in the overall cohort and markedly superior performance in patients younger than 70 years (area under the curve (AUC) 0.945; Youden’s J = 0.871). The optimal BED threshold for predicting PTBE was approximately 41 Gy (α/β = 14), corresponding to ~18 Gy in a single fraction and ~5.8 Gy per fraction in a five-fraction regimen. Conclusions: The BED values calculated using α/β ratios near 14 provide the most reliable estimate of PTBE risk following primary LINAC-based radiotherapy for convexity, parasagittal, and falcine meningiomas. Maintaining prescription doses below this threshold may help reduce the likelihood of PTBE in this patient population.