Effect of radiation dose on the outcomes of gamma knife treatment for trigeminal neuralgia: A multi-factor analysis

Aim: To analyze the effect of different radiation variables on the outcomes of treatment for trigeminal neuralgia (TN). Materials and Methods: Seventy-three patients with refractory TN were treated with a maximum dose of 75-90 Gy using either one (n=41) or two (n=32) isocenters and were intensively followed up. The integrated dose delivered to the trigeminal nerve root within the prepontine cistern and the nerve root volume was calculated using the Gamma-Plan system. Relationships between the clinical outcomes and radiation variables were statistically analyzed using a combination of Fisher's exact test and multivariate analyses. Results: At their last follow up, 21 patients (28.8%), 22 patients (30.1%), 19 patients (26%), 6 patients (8.2%), and 5 patients (6.8%) had Grade I-V pain outcomes, respectively, and the average mean dose delivered to the trigeminal nerve root, average integrated dose (mJ) and nerve root volume in prepontine cistern were 45.29 Gy, 4,26 mJ, and 98.47 mm(3), respectively. The pain relief rate was not significantly improved by a higher amount of integrated dose received by the trigeminal nerve root in prepontine cistern, however, incidence of trigeminal nerve toxicity was increased (P=0.005). Conclusions: Our limited results suggested that a higher integrated dose might increase the incidence of trigeminal nerve toxicity with no significant benefits in pain relief when the maximal doses were within 75-90 Gy. The protocol for increasing radiation variables such as longer nerve exposure length and higher maximal dose is not recommended as a routine approach and more randomized studies with large number of cases would be required to verify the best treatment strategy of gamma knife radiosurgery for TN.