Background and purpose:Medulloblastoma(MB),which is a primitive neuroectodermal tumor(PNET),is the most common malignant brain tumor of childhood.The mean age at diagnosis is 6 years.Due to the tremendous improvements in techniques of radiotherapy and chemotherapy,the 5-year overall survival(OS) is increased to 70% now,compared with 20% in the 1970s.Factors which include local relapse,whether or not there has occurred metastases before resection,residual tumor and age etc.are mostly considered to have significant effects on prognosis.We studied the effects and side effects of the three dimensional conformal radiation therapy(3D-CRT) for the children with medulloblastoma,and summarized the reasons of failure of the therapy.Methods:From August 2001 to August 2007,34 children with medulloblastoma were treated in our hospital.Among all the patients(3-16 years,mean age was 9.5 years) there were 16 cases in high-risk group,and 18 cases in low-risk group.All of them underwent total or subtotal resection before radiation therapy.Patients were not given radiotherapy and chemotherapy before surgery.The interval between surgery and radiotherapy was less than 3 weeks.The 3D-CRT was done for all the patients with the same techniques:30 Gy to the whole cranialspinal axis followed by a boost of 20-25 Gy to the posterior fossa,witha median fraction dose of 180 cGy.Chemotherapy was given according to the protocol which consisted of lomustine,cisplatinum and vincristine after radiotherapy,but the patients were not given intrathecal chemotherapy.Blood counts and chemistries and renal and hepatic evaluations were performed regularly before every course.Results:5-year OS and 5-year event free survival(EFS) were 71% and 62% respectively.The mean follow-up was 36.5 months.The 5-year OS of the high risk group and low risk group were 88.9% and 50.0% respectively.There was significant difference between them(P=0.01).13 patients were failures.Of all failure patients,3 had recurrence in the region of the cribriform plate.The complete remission was 70.5%,and the partial remission was 14%.If metastases were found before surgery,the 5-year OS was 12.5%(1/8),and if the residual tumor was more than 1.5 cm3,the 5-year OS was 0%(0/5).Whether or not the metastases were found before surgery,and the presence of residual tumor,both had significant impacts on the prognosis of the children with medulloblastoma(P