Treatment strategy in stereotactic radiosurgery for trigeminal neuralgia, essential tremor, and coexisting intracranial tumors: The impact of biologically effective dose on clinical outcome

Background: Gamma Knife radiosurgery (GKRS) is a well-established treatment for trigeminal neuralgia (TN) and essential tremor (ET). In patients with coexisting intracranial tumors, radiosurgery can potentially address functional and oncologic targets in a single or staged session. However, data on integrating these treatments and the predictive role of the biologically effective dose (BED), remain limited. This study aims to evaluate clinical outcomes and identify the influence of dosimetric predictors, including BED, in patients undergoing GKRS for TN and/or ET in the context of coexisting intracranial tumors. Methods: This retrospective analysis included 12 patients treated with GKRS for TN and a coexisting intracranial tumor, and two patients treated for ET and a tumor. Clinical outcomes were assessed using Barrow Neurological Institute (BNI) pain and numbness scores. Treatment parameters, including prescribed dose, dose rate, and BED, were analyzed. BED thresholds for response prediction were identified using logistic regression and receiver operating characteristic (ROC) analysis. Results: Clinically meaningful pain relief was observed in 76.5% of all GKRS treatment sessions, including instances where patients underwent repeat GKRS. Among 12 analyzable TN patients (15 treatment sessions), five underwent repeat GKRS for recurrent or persistent pain. Of the patients with available imaging, 50% showed tumor shrinkage, while the remainder were radiological non-responders; two of these three patients were among the five who required repeat GKRS. Repeat treatments were well-tolerated, with no increase in complications or radiation necrosis. BED was significantly associated with early BNI improvement across the cohort (Spearman's ρ = 0.660, p = 0.0054; Pearson's r = 0.718, p = 0.0017, R² = 0.515) and even more strongly in patients with tumor-related TN (ρ = 0.797, p = 0.01). ROC analysis identified BED thresholds predictive of early responders: 1544.9 Gy₂.₄₇ for the full cohort (AUC = 0.78) and 1478.71 Gy₂.₄₇ for the tumor-compression subgroup (AUC = 0.85). Tertile-based BED stratification showed significant differences in pain relief in the tumor-compression group (p = 0.05), but not in the full cohort. Conclusion: GKRS is safe and effective for TN in patients with intracranial tumors. BED appears to be a valuable predictor of early treatment response, particularly in tumor-related TN, where it demonstrated enhanced predictive strength. These findings support integrating BED into treatment planning and highlight the broader utility of radiosurgery in addressing coexisting functional and oncologic pathologies. Prospective studies are warranted to validate these observations and optimize dose-guided strategies.