Abstract: Objective To evaluate the precision of different image guide frequency protocol in the treatment of tumors at different positions. MethodsSixteen thousands sets of megavoltage CT（MVCT） images were collected from 80 patients with tumors at different positions before 20 treatment fractions， including 20 brain， 20 head and neck（H＆N）， 20 thoracic and 20 abdominopelvis. The MVCT images of different guide protocols and planning images were matched as to analyze either the deviation value of every five days protocol and daily protocol or the deviation value of every other day protocol and daily protocol. Meanwhile， the frequency of threedimensional positioning error more than 3mm and 5mm in four different positions were investigated. Results The deviations between every five days protocol and every other day protocol on lateral， longitudinal， vertical were（0.42±0.06）mm，（0.68±0.09）mm，（0.28±0.04）mm for the brain tumors；（0.40±0.06）mm，（0.29±0.12）mm，（0.23±0.13）mm for H＆N；（0.87±0.12）mm，（1.85±0.16）mm，（0.79±0.11）mm for thoracic；（0.83±0.12）mm，（0.19±0.31）mm，（0.95±0.16）mm for abdomino-pelvis. In the every other day protocol： for brain treatments， 12.25％ and 3.25％ of treatment fractions were shifted 3mm and 5mm 3 dimension（3D） vector distance； For H＆N treatments， 18％ and 4.25％ of treatment fractions were shifted 3mm and 5mm 3D vector distance； For thoracic treatments， 23％ and 12％ of treatment fractions were shifted 3mm and 5mm 3D vector distance； For abdominopelvis treatments， 25％ and 13.75％ of treatment fractions were shifted 3mm and 5mm 3D vector distance. Whereas this occurred for 21.75％ and 5％，24.5％ and 8.25％， 36％ and 23％， 34％ and 24.75％ of brain， H＆N， thoracic and abdomino-pelvis. The deviation values of every five days protocol were higher than those of every other day protocol（P＜0.05）. Conclusion Improving the image guide frequency can improve the radiotherapy precision.