Stereotactic Radiotherapy with Fractionation for the Lesions in and Around the Brainstem and Optic Nerve.

Purpose Among the components of the central nervous system, the optic nerve and the brainstem are considered to be the eloquent structures that are sensitive to stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT). SRS or SRT with fractionation in areas adjacent to these tissues is both promising and challenging. Materials and methods To clarify the precise dose distribution achievable with fractionation in and around the optic nerve and brainstem, theoretical simulations were performed, based on the biological effective dose (BED). Results These simulations clearly showed that the doses to the optic nerve and brainstem can be adjusted using fractionation, meaning that the prescribed doses to the surrounding brain tissue can be reduced. Conversely doses to the lesions themselves can be increased by fractionation, while maintaining a stable dose to normal optic nerve and brainstem tissue.