Protection of the anterior visual pathways during gamma knife treatment of meningiomas

Abstract

The anterior visual pathway (AVP) can be at risk during gamma knife surgery (GKS). There is no standardised published methodology for protecting the AVP. This paper suggests such an approach in relation to the treatment of meningiomas. There were 67 patients with a mean age of 48.8 years and a minimum follow-up of 25 months. A recent perimetry was available on the day of treatment. The visual pathway was outlined and the maximum radiation dose was recorded. In some cases a dose volume histogram (DVH) of the AVP was constructed to assess the volume receiving more than the desired maximum dose. The aim was a maximum dose between 8 and 10 Gy. A principle of sub-optimal dose planning was used to protect vision. Follow-up included new visual field examinations. Various anatomical locations place different parts of the AVP at risk. No patient suffered a deterioration of vision. In 21 (38.7%) patients there was an improvement in the visual field and in 7 (44%) associated diplopia improved. Vision could improve without corresponding tumour shrinkage. A standard measure of radiation toleration of the AVP could be the maximum dose within its volume, probably at least 10 Gy. Computerised perimetry should be available on the day of treatment and at follow-up. There is no need to have a distance between the tumour margin and the visual pathway. Sub-optimal dose-planning has been advantageous. Improvement in vision is not necessarily a consequence of tumour shrinkage.

Key words:

• Radiosurgery
• meningioma
• visual pathway
• optic pathway
• adverse radiation effects

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.