Abstract: ObjectiveTo investigate the efficacy and the application value of MosaiQ system in imageguided radiotherapy（IGRT）. MethodsFrom 8 Jan 2014 to 30 May 2017, 510 patients with malignancies receiving IGRT were enrolled. The setup errors required from the first trial and the final trial， and the accelerator treatment bed values before IGRT and after the calibration position were recorded. The tumor setup errors and the treatment accuracy of radiotherapy were analyzed statistically. ResultsThe setup errors of Y direction were the largest compared with X and Z directions（P＜0.05）. Abdominal tumor setup errors were the largest compared with head， head and neck， chest， abdomen and pelvis（P＜0.05）. The difference between the first trial and the final decision had no statistical significance （P＞0.05）， and the mean value of setup errors was less than 2 mm. The treatment accuracy for all parts had no differences （P＞0.05）， and the accuracy was more than 800％. The accuracy of Y direction was 84.7％， lower than X and Z directions （P＜0.05）. ConclusionMosaiQ system can achieve allround monitoring of IGRT， improve the accuracy of treatment， and provide theoretical and data support for quality control and assurance in the department of radiotherapy.

Key words: Imageguidance radiotherapy（IGRT）, MosaiQ, Setup errors, Treatment accuracy