Abstract: Objective To compare the dosimetric advantages and disadvantages of conventional radiotherapy （CRT）and helical tomotherapy（HT）for patients treated with craniospinal irradiation. Methods 10 patients treated with craniospinal irradiation were enrolled. The scanning CT images were transmitted to Treatment Planning System（TPS）， where painting the volumes of tumors and organ at risks（OARs）. CRT and HT plan were designed for each patient simultaneously with the same prescription dose（PTV DT 36Gy／18f）. Then the homogeneous index（HI）， conformity index（CI）， the dose distributions of planning target volume coverage， dosevolume histogram（DVH）and organ at risks were analyzed with TPS.
ResultsHI， CI and DVH in HT plan were superior to CRT plan（P＜0.05）. The maximum dose（Dmax） and mean dose （Dmean） of target areas in both groups were larger than prescribed dose（36Gy）， especially HT group was more close to 36Gy（P＜0.05）. V95， V107 in the two plans was（98.0±1.2）％，（34.7±18.9）％ and（99.2±0.3）％，（0.6±1.3）％ with significant difference （P＜0.05）. The Dmean of other OAR in HT plan was lower than that of CRT plan except for bone marrow and Body. There was significant difference for Dmean of OAR such as eyeball， heart and Body （P＜0.05）. The V5 of other OAR in HT plan was higher than that of CRT except for eyeball. There was significant difference for V5 of OAR such as lung， heart， stomach， liver， kidney， bone marrow and Body（P＜0.05）. Difference was not siginificant for V10 of OAR（P＞0.05）. The V20 of other OAR in HT plan was lower than that of CRT plan except for Body. There was significant difference for V20 of OAR such as eyeball， lung， heart， stomach， kidney and liver（P＜0.05）. Conclusion HT plan is superior to CRT plan in craniospinal irradiation. However， the longterm effects of tomotherapy dose avoidance on large volume low dose radiation are not yet known.