Delineation of radiation therapy target volumes for cutaneous malignancies involving the ophthalmic nerve (cranial nerve V-1) pathway.

Abstract

The ophthalmic nerve (cranial nerve V-1) runs in close proximity to the globe, optic nerve, chiasm, and brain. The purpose of this study was to provide contouring guidance using computed tomography (CT)-identifiable landmarks, based on an analysis of skin cancer patients with V-1 invasion. Radiation oncology planning CT scans were analyzed for landmarks to guide V-1 target delineation from the skin surface to the trigeminal ganglion. Axial and coronal magnetic resonance imaging (MRI) sequences were fused with the planning CT to confirm soft-tissue findings and identify enhancement related to perineural spread. CT/MRI-based anatomic landmarks were catalogued and described on an atlas. Soft-tissue and bony landmarks were confirmed as consistently identifiable on CT with assistance from fused MRI. A reference atlas was developed that shows the entirety of the V-1 pathway on consecutive CT slices. Initial delineation of the V-1 pathway can be accomplished using CT-visualized landmarks confirmed on fused MRI. This CT/MRI atlas will assist radiation oncologists in delineation of the V-1 pathway.