Assessment of inter-fractional positional accuracy of anterior visual pathway in a frameless stereotactic radiosurgery using an MR-simulator

In hypofractionized stereotactic radiosurgery (SRS), radiation-induced optic neuropathy (RION) might associate with the local radiation injury to anterior visual pathway (AVP), while the irradiated dose to AVP is much influenced by its positional variation. We for the first time assessed the inter-fractional AVP positional variation in a hypofractionized frameless SRS setting on 13 volunteers using a 1.5T MR-simulator. The results suggested that sub-millimeter AVP positional accuracy could be achieved in the frameless SRS after brain alignment. However, the dose uncertainty in the most anterior optical nerves should be concerned (1.2±2.6 mm positional variability) in a sharp dose gradient of SRS.