Purpose:The most common type of cancer among women is breast cancer.Accurate assessment of skin dose in radiotherapy can provide useful information for clinical consideration.The aim of this study is assessment of skin dose in breast cancer radiotherapy with 6 MV photon beam of a medical linac.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 for various positions on the fields using EBT3 radiochromic film.The films were scanned by a 1000XL Microtek color scanner.Similar conditions of measurement on and RANDO phantom,including field size,angle of irradiation,number of fields and etc.,were simulated with MCNPX Monte Carlo code.Dose values for corresponding points from two methods were compared.Results:In dosimetry with radiochromic films on RANDO phantom,there were points having underdosage and overdosage based on the prescribed dose and skin tolerance levels.85%of points had underdosage and 15%of points had overdosage.In some cases,relatively large differences were observed between the Monte Carlo and measurement results of skin dose.Conclusions:Based on the interpretation of the results of the points which have underdosage,it is suggested that bolus be used for those points.For the overdosage points the skin tolerance dose should be considered.The reason for the difference observed between the measurement and simulation results can be relevant to the effect of angle of beam incidence,voxel size and MCNPX tally type which was used.