Purpose:Radiochromic EBT3 film is a later generation of radiochromic films.The aim of this study is to compare EBT and EBT3 radiochromic films in radiotherapy fields of breast cancer.Methods:A RANDO phantom was irradiated by a 6 MV Siemens Primus linac with medial and lateral fields of radiotherapy of breast cancer.Dosimetry was performed in various points in the fields using EBT and EBT3 films.Films were scanned by a Microtek color scanner.Dose values from two films for corresponding points were compared.Results:In the investigation of calibration,net optical density(NOD)of EBT radiochromic is more than the EBT3 film.The highest percentage difference between NODs of two films is related to 0.75 Gy and equals to 14.19%.The lowest value is related to 0.2 Gy dose and is equal to 3.31%.The highest percentage difference between two films on the RANDO phantom in breast cancer fields is 13.51%and the minimum value is equal to 0.33%.Conclusion:From the comparison between the two films,most of the points show differences in dose in the measurements in the fields of breast cancer radiotherapy.These differences are attributed to the thickness of the active layers,the overall thickness of the films,and the difference in the calibration fitted functions.The advantage of EBT film over EBT3 is a higher sensitivity,on the other hand,EBT3 film allows to use its both sides in the scanning process and it is a new version of this film type.