Objective To investigate the effect of field angle on the results of in vivo dose validation of electronic portal imaging device(EPID)in patients.Methods Design the mold test and analyze the influence of different mold thicknesses and different frame angles on the 2D γ pass rate.Twenty-three patients who un-derwent radiotherapy in the Department of Radiotherapy of Jinhua Municipal Central Hospital from January to June 2023 were selected as the research object.In vivo dose verification was carried out during treatment to obtain 2D γ pass rate using same-day sector beam CT(FBCT)of planned CT and executive image guided(IG-RT)as reference images,and the influence of field angle on pass rate was analyzed.Results When the frame angle was unchanged,the area of the shooting field was larger than 17 cm×17 cm,and the 2D γ passing rate decreased with the increase of the thickness.The frame angle had no effect on the 2D γ pass rate when the mold thickness was constant.In clinical treatment data,the passage rate of 2D γ near 0°/180° was higher than that near 90°/270°(P＜0.05),and the passage rate near 90°/270° in the FBCT group was higher than that in the IGRT group(P＜0.05).The median passing rate of 3 mm 2D γ was 97.97％in 3％of the 23 patients.The non-IGRT group was 96.81％,the IGRT group was 97.89％,the FBCT group was 98.94％.There was a statistically significant difference in 2D γ passing rate between the non-IGRT group and the IGRT group(Z=-5.083,P＜0.05),and there was a statistically significant difference in 2D γ passing rate between the IGRT group and the FBCT group(Z=-10.657,P＜0.05).Conclusion Clinically,the difference of pass rate in vi-vo dose verification at different rack angles is mainly due to the difference of images within and between ses-sions.Using same-day FBCT as the reference image for in-vivo dose verification can improve the accuracy of pass rate and eliminate the influence of image difference between sessions.