Beyond the physical dose: implications of biologically effective dose variations in the stereotactic radiosurgical treatment of trigeminal neuralgia

OBJECTIVE: Biologically effective dose (BED)-oriented planning is emerging as a potential key consideration in future planning strategies, aiming to achieve the best, most personalized radiosurgery treatment plans possible. In this study, planning parameters and BED variations in previously treated patients were investigated to determine the factors that affect the treatment results in order to achieve better patient outcomes. METHODS: A highly refined cohort of 191 idiopathic, type 1 trigeminal neuralgia (TN) patients who underwent stereotactic radiosurgery (SRS) with 80 Gy as a first-line invasive treatment were investigated. Follow-up data were obtained from the retrospective analysis of a prospectively maintained database. RESULTS: As the shot distance from the root entry zone (REZ) increased by each millimeter, the hazard ratio (HR) for relapse increased by 16.3%, and the HR was reduced by 4% for every 10% increase in the BED that the REZ received. The odds of being medication free at the end of follow-up were reduced by 21.5% for every millimeter that the shot was positioned more distally. On the other hand, multivariate analysis showed that the maximum BED applied to the nerve was a positive predictor of new numbness, when corrected for pain duration before SRS, plugging, and age at treatment. CONCLUSIONS: For patients with TN, positioning the shot closer to the REZ and applying a higher BED to this area provides better pain control in the long term compared to more distally placed shots. As expected, a higher maximum BED applied to the nerve was associated with an increased risk of developing facial numbness.