Medulloblastomas are rare after puberty. Medulloblastomas recur frequently, and toxicity of treatment is of concern. To date, no prospective randomized clinical trials in adults have been published. Therefore, the EORTC 1634-BTG/NOA-23 trial for post-pubertal patients with standard-risk medulloblastoma aims to increase treatment efficacy and decrease treatment toxicity. Patients will be randomized to standard and reduced radiation therapy, and patients in the SHH subgroup will also be randomized to a group in which the SMO inhibitor sonidegib (OdomzoTM, Sun Pharmaceuticals Industries, Inc., New York, USA) will be administered in addition to standard radiation chemotherapy rather than standard radiation chemotherapy alone. In complementary studies, we will examine tumor tissue, blood and cerebrospinal fluid samples, magnetic resonance images, and radiation schedules to gain information that may improve future treatment. Patients will also be monitored long-term for late effects of therapy, health-related quality of life, cognitive function, social and occupational quality of life, and reproduction and fertility.