Objective To analyze the performances of electronic portal imaging device (EPID) in mechanical and dosimetry responses,and to investigate the feasibility of adopting EPID as a daily quality assurance (QA) equipment. Methods The EPID of Trilogy linear accelerator was tested for mechanical position repeatability and dose linear response. Then,a group of special fields were edited manually for simulations of field translation and symmetry deviations,and the sensitivities of EPID and MyQA Daily to field translation and symmetry deviations were evaluated,and moreover,the linear correlation between the set value and the measured value was analyzed. Finally,daily QA was conducted with EPID and MyQA Daily for 30 consecutive days,and the measurement results and time consumption were analyzed. Results The maximum deviation of EPID position repeatability was 0.4 mm,and the dose response was linearly correlated (R2>0.999). The symmetry deviation test results showed that both of EPID and MyQA Daily were capable to effectively detect the 0.2％ offset in symmetry,and a linear correlation was demonstrated between the set value and the measured results (R2>0.995). In translation test,the linear correlation of EPID was more explicit than that of MyQA Daily (R2=0.992 vs R2=0.976). In daily QA,all the measured results of EPID and MyQA Daily were within the clinic acceptance tolerance. Moreover,the mean value of Y-directional symmetry and flatness measured by EPID was approximately 1.00％ larger than MyQA Daily. The average time required by EPID was 50 s less than MyQA Daily[(129.97±4.16) s vs (184.53±4.23) s]. Conclusion EPID can be served as a reliable and efficient daily QA equipment for linear accelerator. However,it is not capable to be used as a criterion for evaluating linear accelerator performance.

Objective To analyze the performances of electronic portal imaging device (EPID) in mechanical and dosimetry responses,and to investigate the feasibility of adopting EPID as a daily quality assurance (QA) equipment. Methods The EPID of Trilogy linear accelerator was tested for mechanical position repeatability and dose linear response. Then,a group of special fields were edited manually for simulations of field translation and symmetry deviations,and the sensitivities of EPID and MyQA Daily to field translation and symmetry deviations were evaluated,and moreover,the linear correlation between the set value and the measured value was analyzed. Finally,daily QA was conducted with EPID and MyQA Daily for 30 consecutive days,and the measurement results and time consumption were analyzed. Results The maximum deviation of EPID position repeatability was 0.4 mm,and the dose response was linearly correlated (R2>0.999). The symmetry deviation test results showed that both of EPID and MyQA Daily were capable to effectively detect the 0.2％ offset in symmetry,and a linear correlation was demonstrated between the set value and the measured results (R2>0.995). In translation test,the linear correlation of EPID was more explicit than that of MyQA Daily (R2=0.992 vs R2=0.976). In daily QA,all the measured results of EPID and MyQA Daily were within the clinic acceptance tolerance. Moreover,the mean value of Y-directional symmetry and flatness measured by EPID was approximately 1.00％ larger than MyQA Daily. The average time required by EPID was 50 s less than MyQA Daily[(129.97±4.16) s vs (184.53±4.23) s]. Conclusion EPID can be served as a reliable and efficient daily QA equipment for linear accelerator. However,it is not capable to be used as a criterion for evaluating linear accelerator performance.