MedulloblastomaCerebellar NeoplasmsNeuroectodermal Tumors, PrimitiveHedgehog ProteinsBrain NeoplasmsCranial IrradiationInfratentorial NeoplasmsCerebellumAnaplasiaEpendymomaCell Line, TumorBasal Cell Nevus SyndromeVeratrum AlkaloidsCranial Fossa, PosteriorChromosomes, Human, Pair 17Gene Expression Regulation, NeoplasticCell ProliferationCombined Modality Therapy