The Impact of Optic Nerve Movement on Intracranial Radiation Treatment

Purpose: In radiotherapy, high radiation exposure to optic nerve (ON) can cause optic neuropathy or vision loss. In this study, we evaluated the pattern and extent of the ON movement using MRI, and investigated the potential dosimetric effect of this movement on radiotherapy. Methods: : Five volunteers were requested to gaze toward five directions during MRI acquisitions, including neutral (straight forward), left/right (horizontal movement), and up/down (vertical movement). The motion of the ON was analyzed quantitatively. To evaluate the potential dosimetric effect of this motion, the ON motion was hypothetically applied to three patients with perioptic tumors. Results: : The motion of ON followed a nearly conical shape among all five subjects. The anterior end of ONs moved with 10.4 ± 2.2 mm and 11.1 ± 1.4 mm horizontally for the left and right eyes, and 9.3 ± 0.8 mm vertically for the right eye. Posterior end of ON has negligible displacement. In the three clinical scenario, the hypothetical movement of ON in this measured range introduced non-negligible dosimetric effect. Conclusion: The range of motion of the anterior portions of the optic nerves is on the order of centimeters, which may need to be considered with extra attention during radiation therapy workflow.