Optic Nerve Movement May Need to be Considered When Treating with Stereotactic Radiosurgery

Abstract

Introduction: Fractionated stereotactic radiosurgery (fSRS) is an effective definitive treatment for optic nerve (ON) tumors. It is controversial whether treatment to the ON requires attention to the position of the eye as some consider the movement to be negligible. We investigated in four patients to establish whether there is clinically significant displacement of the ON as the globe moves and the effect this may have on target coverage in fSRS treatments. Method: Four patients receiving radiotherapy treatment to the skull and requiring cone beam computed tomography (CBCT) matching were asked to look in different directions as routine CBCT were obtained. An fSRS plan was created, treating the ON with the patient looking straight ahead. The displacement of the ON from straight was measured, with the patient looking fully left or right, the DVH of the optic nerve in the three locations was compared. Results: The data collected showed that there could be a significant difference in optic nerve position as the patient’s gaze changed. The DVH showed that the PTV coverage was affected as the patient moved their gaze either left or right by up to 9% (95%CI is from -15% to -3%, p=0.012). Conclusion: As a result of our study we recommend cooperative patients receive some training to ensure that optic nerve positioning is maintained throughout simulation and treatment.