Abstract: Objective We aimed to explore the difference of dosimetry among intensity modulated radiation therapy(IMRT),volumetric modulated arc therapy(VMAT)and helical tomotherapy(TOMO)in the radiotherapy of medulloblastoma.Methods Ten children's patients with the medulloblastoma were selected and designed in this study.A clinically feasible radiotherapy plan was designed for IMRT(5 fields),VMAT and TOMO.Conformality index(CI),homogeneity index(HI),V₁₀₇,maximum dose(D_max),organ at risk(OAR)dose-volume level,monitor units and treatment time were used to analyze in these groups.Results CI,HI,V₁₀₇,D_max and OAR of target areas were significantly superior to VMAT and IMRT in the TOMO group of target PTV for whole brain full radiotherapy.The organ at risk dose-volume level in the TOMO group was lower than that in VMAT and IMRT(5 fields)groups(P＜0.05).The TOMO group also had the most monitor units and the longest treatment time(P＜0.05).Hence,the patients in the TOMO group could irradiate completely the whole brain and full spinal cord without moving treatment couch to avoid the error from the man-made movement in VMAT and IMRT(5 fields)treatments.Conclusion In the radiotherapy of medulloblastoma,the dose distribution of patients in the TOMO group are superior to the VMAT and IMRT groups(5 fields).However,the number of monitor units and treatment time is significantly increased during treatment,and its clinical effect needed to be further studies.

Key words: Intensity modulated radiation therapy, Volumetric modulated arc therapy, Helical tomotherapy