title: Optic radiation tractography integrated into simulated treatment planning for Gamma Knife surgery.
abstract: OBJECTIVE
  No definitive method of preventing visual field deficits after stereotactic radiosurgery for lesions near the optic radiation (OR) has been available so far. The authors report the results of integrating OR tractography based on diffusion tensor (DT) magnetic resonance imaging into simulated treatment planning for Gamma Knife surgery (GKS).
  
  
  METHODS
  Data from imaging studies performed in 10 patients who underwent GKS for treatment of arteriovenous malformations (AVMs) located adjacent to the OR were used for the simulated treatment planning. Diffusion tensor images performed without the patient's head being secured by a stereotactic frame were used for DT tractography, and the OR was visualized by means of software developed by the authors. Data from stereotactic 3D imaging studies performed after frame fixation were coregistered with the data from DT tractography. The combined images were transferred to a GKS treatment-planning workstation. Delivered doses and distances between the treated lesions and the OR were analyzed and correlated with posttreatment neurological changes.
  
  
  RESULTS
  In patients presenting with migraine with visual aura or occipital lobe epilepsy, the OR was located within 11 mm from AVMs. In a patient who developed new quadrantanopia after GKS, the OR had received 32 Gy. A maximum dose to the OR of less than 12 Gy did not cause new visual field deficits. A maximum dose to the OR of 8 Gy or more was significantly related to neurological change (p < 0.05), including visual field deficits and development or improvement of migraine.
  
  
  CONCLUSIONS
  Integration of OR tractography into GKS represents a promising tool for preventing GKS-induced visual disturbances and headaches. Single-session irradiation at a dose of 8 Gy or more was associated with neurological change.
authors.affiliation: Departments of Neurosurgery, The University of Tokyo Hospital, Tokyo, Japan. kskmaru-tky@umin.ac.jp
authors.forename: Keisuke
authors.initials: K
authors.lastname: Maruyama
authors.forename: Kyousuke
authors.initials: K
authors.lastname: Kamada
authors.forename: Masahiro
authors.initials: M
authors.lastname: Shin
authors.forename: Daisuke
authors.initials: D
authors.lastname: Itoh
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Masutani
authors.forename: Kenji
authors.initials: K
authors.lastname: Ino
authors.forename: Masao
authors.initials: M
authors.lastname: Tago
authors.forename: Nobuhito
authors.initials: N
authors.lastname: Saito
mesh_terms: D000293:Adolescent; D000328:Adult; D001931:Brain Mapping; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D006261:Headache / Q000517:prevention & control; D006801:Humans; D021621:Imaging, Three-Dimensional; D002538:Intracranial Arteriovenous Malformations / Q000473:pathology / Q000601:surgery*; D008297:Male; D011183:Postoperative Complications / Q000517:prevention & control; D011300:Preoperative Care; D011874:Radiometry; D016634:Radiosurgery / Q000379:methods*; D012189:Retrospective Studies; D013238:Stereotaxic Techniques; D014786:Vision Disorders / Q000517:prevention & control*; D014793:Visual Cortex / Q000601:surgery*