Optic radiation tractography integrated into simulated treatment planning for Gamma Knife surgery

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Object

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.

Abbreviations used in this paper:AVM = arteriovenous malformation; CT = computed tomography; DICOM = Digital Imaging and Communications in Medicine; DT = diffusion tensor; GKS = Gamma Knife surgery; MR = magnetic resonance; OR = optic radiation.

Article Information

Address correspondence to: Keisuke Maruyama, M.D., Ph.D., Department of Neurosurgery, The University of Tokyo Hospital, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan. email: kskmaru-tky@umin.ac.jp.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Case 1. Upper and Middle: Radiosurgical dosimetry images showing the results of OR tractography (with the OR tract in orange) in an 18-year-old man who developed quadrantanopia 37 months after GKS. The maximum dose to the OR was 32 Gy. The spatial relationship between the dose distribution and the OR was clearly demonstrated in a 3D CT reconstruction (upper right). The yellow object represents the volume that received 20 Gy. The green mesh and the light blue mesh correspond to the volumes that received 10 and 5 Gy, respectively. Lower: The results of visual field testing performed 37 months after GKS showing right upper quadrantanopia in both eyes.

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    Case 5. Radiosurgical dosimetry images showing the results of OR tractography (OR tract in orange) in a 40-year-old woman who presented with migraine with aura. Her migraine was unchanged for 31 months after GKS, which was administered at a maximum of 7.6 Gy to the OR. In the 3D reconstruction (upper right), the yellow object represents the volume that received 20 Gy. The green mesh and the light blue mesh correspond to the volumes that received 10 and 5 Gy, respectively.

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    Case 7. Radiosurgical dosimetry images showing the results of OR tractography (OR tract in orange) in a 39-year-old man who had an incidentally diagnosed occipital AVM. The maximum dose to his OR was 7.6 Gy. He showed no symptoms during 18 months of follow-up after GKS. In the 3D reconstruction (upper right), the yellow object represents the volume that received 20 Gy. The green mesh and the light blue mesh correspond to the volumes that received 10 and 5 Gy, respectively.

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