To assess the efficacy and safety in average-risk pediatric medulloblastoma (MB) receiving tumor bed boost irradiation compared to a posterior fossa (PF) boost. Thirty patients were enrolled in the study and divided evenly into two treatment arms of 15. Both arms received 23.4 Gy craniospinal irradiation (CS) and a 32.4 Gy boost. Patients in arm 1 were given PF boosts, and those in arm 2 were given boosts to the gross target volume (GTV). Weekly oncovin was given throughout all radiotherapy

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... . Eight cycles of adjuvant chemotherapy of CCNU, oncovin and platinol were given to all patients after RT. MRI, pure tone audiogram (PTA) and intelligence quotient (IQ) tests were performed before and after RT and every three months thereafter. There were significant differences in the sparing dose to the cochlea and brain stem as well as the volume of the normal brain receiving a 100% dose. There was a significant initial improvement of hearing function in patients given the target volume boost after RT, which was lost after chemotherapy. With a median follow up of 23 months, there was no difference in progression free survival or overall survival between the two arms. Irradiation of the tumor bed after 23.4 Gy craniospinal irradiation for average-risk MB results in similar disease control as a PF boost. Dosimetric sparing for the cochleae and normal tissue is evident in patients receiving tumor bed boosts. The hearing improvement and cognitive function preservation effects of the treatment need more follow up.