EQD2 = D * [(d + α/β)/(2 + α/β) = 38,2 Gy where D is the altered schedule total dose, d is the altered daily dose. Then, considering the differences between the overall treatment time between conventional fractionated and hypofractionated treatment (28 fractions, 5 fractions per week, 38 total days and 5 fractions, 5 days respectively), assumed Dprolif = 0,7 as for the most of the tumours (7, 17), where Dprolif is the dose recovered daily owning to proliferation: EQD2,T = EQD2,t - [(T - t) * Dprolif ] = 61 Gy Treatment planning. Patients will have a 1.25 mm thickness MRI, including fat suppression sequence, T1with Gadolinium sequence and a contrast-enhanced CT scans. The images will then merged in order to optimize the definition of the target volume and the intra-extraorbital segment of the optic nerve, and the organ at risk (i.e. retina) An inverse planning software will be adopted to optimize the target coverage and at the same time to achieve the maximum of conformality and homogeneity of the prescription dose. The treatment plan used for each treatment will be based on an analysis of the volumetric dose including dose-volume histogram (DVH) analyses of the PTV and critical normal structures. The number of paths and beams used for each patient will vary and will be determined by the selected individual treatment plan.