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Track Based Tractography Delineates Microstructural Changes in the Facial and Trigeminal Nerve After Gamma Knife Radiosurgery

R Juh*, J Han , C Kim , C Oh , Seoul National University Bundang Hospital Gamma Knife CenterSeongnam


(Wednesday, 7/17/2019) 9:30 AM - 10:00 AM

Room: Exhibit Hall | Forum 8

Purpose: Focal radiosurgery is a common treatment modality for trigeminal neuralgia (TN), a neuropathic facial pain condition. The efficiency of radiosurgery is related to its highly precise targeting. We also studied the applied radiation dose within the area of focal contrast enhancement on the trigeminal nerve. Since diffusion tensor imaging (DTI) provides information on white matter microstructure, we explored the feasibility of trigeminal nerve tractography and assessment of DTI parameters to study microstructural changes after treatment.

Methods: Sixteen TN patients (2 females, 4 male, average age 65.3 years) treated with Gamma Knife radiosurgery, 40 Gy/50 % isodose line underwent 1.5Tesla MR trigeminal nerve . Radiation dose delivered at the borders of contrast enhancement was evaluated.Fractional anisotropy (FA), radial (RD) and axial (AD) diffusivities were calculated for the radiosurgical target area defined as the region-of-interest. Areas outside target and the contralateral nerve served as controls. Follow up MRI was spatially coregistered to the radiosurgical planning MRI

Results: The median deviation of the coordinates between the intended target and the center of contrast enhancement was within 1mm. The radiation doses fitting within the borders of the contrast enhancement the target ranged from 37.5 to 40 Gy. Trigeminal tractography accurately detected the radiosurgical target. Radiosurgery resulted in 47% drop in FA values at the target with no significant change in FA outside the target, suggesting that radiosurgery primarily affects myelin. Tractography was more sensitive, since FA changes were detected regardless of trigeminal nerve enhancement.

Conclusion: DTI parameters accurately detect the effects of focal radiosurgery on the trigeminal nerve, serving as an in vivo imaging tool to study TN. This study is a proof of principle for further assessment of DTI parameters to understand the pathophysiology of TN and treatment effects.


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