Purpose: To evaluate the Edose system, a novel three-dimensional (3D) in vivo dose monitoring system based on electronic portal imaging device (EPID), prior to clinical application, we analyzed the preliminary clinical data using Edose system in patients receiving intensity-modulated radiation therapy (IMRT). Materials and methods: After the physical modeling, the measured results from the Edose system were examined in homogeneous and inhomogeneous phantoms, respectively. To verify the accuracy of the Edose system, we compared its results with testing results from ionization chamber, measurement matrix (Delta4) and dosimetric films. The dosimetric performance of the Edose system was evaluated in 12 randomly selected patients with IMRT and VMAT, and the measured results were compared with the treatment plans. Results: Compared with the measured results, the dose difference at the center of target volume was (0.12 +/- 0.91)% and (0.03 +/- 0.85)%, the gamma pass rate was (94.18 +/- 1.69)% and (95.24 +/- 1.62)% (3mm/3%) for homogeneous and inhomogeneous phantoms, respectively. For IMRT patients, the dose difference at the center of target volume was (0.75 +/- 1.53)%, and the gamma pass rates were (89.11 +/- 3.24)% (3mm/3%) and (96.40 +/- 1.47)% (3mm/5%), respectively. Compared with the results of DVH, the maximum differences of PTVs and mostly organs at risk were all within 3%. For VMAT patients, the. pass rates were (93.04 +/- 2.62)% (3mm/3%) and (97.92 +/- 1.38)% (3mm/5%), respectively. Conclusions: In vivo dose monitoring may further improve the safety and quality assurance for radiation therapy. But rigorous clinical testing is required before putting the existing commercial systems into clinical application. In addition, more clinical experiences and better workflows for using the Edose system are needed.