Objective To investigate the consistency of regions of interest (ROI) volume among different radiological treatment planning systems (TPS) for the same group of patient data, and analyze the tendency and degree of differences caused by data transfer. Methods Between October 2010 and December 2013, the data of 10 nasopharyngeal carcinoma patients treated in West China Hospital were transferred from Monaco TPS into various other treatment planning systems. Based on different ROI volumes, they were divided into 8 groups. We counted the volume differences between these TPS and Monaco TPS, and carried out the statistical analysis. Results For small ROI volume, the calculated difference reached up to 65% in our study. As a general trend, differences became less and less with the increasing of volumes. But for single ROI, the volume difference was likely to vary randomly. The percentage of ROI volumes which were smaller than that of Monaco TPS was 70% for Raystation TPS, 38.75% for Pinnacle TPS, 88.75% for Eclipse TPS, 97.5% for Masterplan TPS, and 83.13% for iPlan TPS. Conclusions ROI volume differences exist generally among different treatment planning systems when ROIs are transferred among them by DICOM protocol. The volume variations may be affected by multiple factors. The volume consistency should be evaluated before any direct comparison of dose volu me histogram parameters which are done between different systems.