3533 - Durable Clinical Response Following Radiosurgery for Trigeminal Neuralgia is Predicted by Volumetric Dose Distribution to the Cisternal Portion of the Nerve
Presenter(s)
M. A. Shohayeb1, Z. Wei2, T. Almeida3, S. G. Ellsworth1, J. C. Flickinger Sr4, L. D. Lunsford3, C. G. Hadjipanayis3, G. Zenonos3, S. Choi1, C. T. Wilke1, B. Elgohari1, A. Niranjan3, and A. H. Zureick1; 1Department of Radiation Oncology, UPMC Hillman Cancer Center, Pittsburgh, PA, 2University of Pittsburgh, Pittsburgh, PA, 3Department of Neurological Surgery, UPMC Center for Image Guided Neurosurgery, University of Pittsburgh School of Medicine, Pittsburgh, PA, 4UPMC Hillman Cancer Center, Pittsburgh, PA
Purpose/Objective(s): A non-invasive stereotactic radiosurgery (SRS) instrument for trigeminal neuralgia (TN) with a maximum dose (Dmax) of 70-90 Gy has a high response rate. The most frequently reported variables include the target location, number of isocenters, and Dmax. Yet, the lack of reporting of volumetric dose distribution related to total nerve volume, which accounts for individual differences in patient anatomy, may impact treatment efficacy and toxicity. Here we aim to better describe dosimetric predictors of outcomes following GKSRS for TN.
Materials/Methods: GKSRS plans from 2017-2020 were reviewed. Exclusion criteria included prior ipsilateral GKSRS or multiple prior surgical procedures for TN. The cisternal portions of the trigeminal nerves were contoured, and DVH datapoints were obtained both as absolute volumes and ratios of the total nerve volume. Response was defined as a documented improvement in symptoms, with or without medication de-escalation, whereas failure was defined as progressive symptoms requiring medication re-escalation or the need for a second procedure. Facial numbness was classified according to the Barrow Neurological Institute (BNI) scale, based on chart review. DVH variables were compared among groups using the Mann-Whitney U test.
Results: Forty-five patients (median age, 69 years) were included in this analysis; all were treated with a proximal target and a single isocenter. The median prescription Dmax was 80 Gy; only one patient received a Dmax below 70Gy. Response rate (i.e., symptomatic improvement) was 84.4% (38/45), with 11 patients (24.4%) able to discontinue all medications. After a median of 27 months post-GKSRS, 22 patients (57.9%) developed recurrence, 17 of whom required further procedures. Facial numbness occurred in 10 patients (22.2%), with only four patients experiencing BNI grade III numbness. The median V70Gy for patients who had a durable response was 21.0% vs. 15.8% for those who failed to have an initial response or who experienced recurrence (P = 0.048). Among patients with facial numbness after treatment, those with BNI grade III had a higher median V50Gy of 51.7% compared to patients with no numbness (47.2%, P = 0.47), while the brainstem D0.03cc was higher in patients without numbness compared to those with numbness (13.4 Gy vs. 10.2 Gy, P = 0.35). None of the seven patients who had V50Gy < 35% experienced BNI grade III facial numbness, and only one experienced facial numbness of any grade.
Conclusion: In our review, we observed that patients with durable response had a significantly higher V70Gy for the entire cisternal portion of the trigeminal nerve. A trend toward higher V50Gy was observed in patients who developed facial numbness with rarely any toxicity observed when V50Gy < 35%. Volumetric dose distribution, normalized to individual nerve anatomy, may help with accurate comparisons between planning techniques in predicting outcomes.