6、ulatorandalinearacceleratorelectronicportalimagingdevice(EPID),respectively.EPIDwasusedtomeasureandcalculatesetuperrorsofrepeatedpositioningfrombeamcentersattheleftandright(Xaxis),thehead(Yaxis)andthefrontandback(Zaxis).Andthen,efficacyofthethreepositioningmethodswereevaluated. Result