This chapter describes the planning aspects of proton beam therapy for pediatric brain malignancies, focusing on optimizing proton radiotherapy through improved modeling and optimization of relative biological effectiveness (RBE) and linear energy transfer (LET). Proton therapy offers potential advantages over conventional photon therapy owing to its depth dose characteristics, including the Bragg peak, the limited exit dose, and the minimized integral dose, thus making it particularly appealing for pediatric patients. Various proton RBE models, including the Local Effect Model (LEM), Microdosimetric Kinetic Model (MKM), and Repair-Misrepair Fixation Model (RMF), and approaches to RBE/LET optimization in treatment planning are discussed. Understanding and incorporating LET and RBE considerations into proton therapy planning may lead to improved treatment outcomes and reduced long-term toxicities for pediatric CNS tumors.