What constraints do you use for the normal brain when treating large CNS tumors with standard fractionation?  

With photon therapy, we use guidance (not absolute), using the following principles, when using 1.8 to 2 Gy per fraction:  Lenses max dose 7-10Gy   Optic Chiasm and optic nerves max dose < 60Gy without chemotherapy and 56Gy with chemotherapy.   Retina max dose < 50Gy with...