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