Apparent diffusion coefficient and magnetic resonance imaging characteristics in predicting response to radiosurgery in patients with vestibular schwannomas.

Objective: Predicting treatment response in patients with vestibular schwannomas (VSs) remains challenging. This study aimed to evaluate the use of pre-treatment normalized apparent diffusion coefficient (nADC) values and magnetic resonance (MR) imaging characteristics in predicting treatment outcomes in patients with VSs undergoing radiosurgery.

Methods: The MR images of 44 patients with VSs who underwent radiosurgery at our institution were retrospectively reviewed, and the patients were categorized into tumor control (n = 28) and progression (n = 16) groups based on treatment response after treatment initiation, with a median follow-up duration of 29.5 (13-115) months. Pre-treatment nADC values for the whole tumor and solid portion of the tumor were assessed for predictive significance. MRI characteristics were analyzed, including hemorrhage status, tumor morphology, and post-treatment loss of central enhancement. Interobserver reliability was also evaluated.

Results: Early post-treatment enlargement was associated with tumor progression (p = .024). The mean pre-treatment nADC values for the solid part of the tumor were significantly higher in the tumor control group than in tumor progression group (1.32 vs 1.05, p = .005). The receiver operating characteristic curve analysis revealed a mean nADC of 1.18 as an optimal cutoff, with sensitivity and specificity of 76.2% and 86.7%, respectively, in predicting treatment response.

Conclusion: The mean nADC values for the solid part of the tumor demonstrated predictive value for treatment response, with implications for treatment planning. Notably, early post-treatment enlargement was correlated with tumor progression. Incorporating these findings into clinical practice may refine treatment strategies for patients with VSs undergoing radiosurgery.