Purpose: Image guided radiotherapy has been broadly employed to correct patient positioning and track the tumor movement.In order to obtain an accurate and fast patient setup before each fractioned treatment,an independent image guided positioning and tracking system was developed,combining infrared tracking and trail-mounted dual X-ray imaging techniques.Method: The basic workflow of the system includes patient information management,X-ray image acquisition,marker-based image registration as well as infrared based motion tracking.Experiments and simulations including static and dynamic localization accuracy as well as reproducibility have been carried out to verify the efficiency of the system.For the infrared based tracking,measurements of known translational(up to 55.0 mm)set-up errors in three dimensions have been performed on a calibration phantom.All the evaluations were conducted based on the AAPM 147 task report with different phantoms and platforms.The accuracy of positioning was evaluated on an anthropomorphic phantom with five markers attached to the surface; the precision of the tracking ability was investigated through a sinusoidal motion platform.For the monitoring of the respiration,ten volunteers contributed to the breathing testing in real time.Results: The reproducibility of position variations was between 0.01 and 0.04 mm.The standard deviation of static marker localization was 0.26mm.The repositioning accuracy was 0.19 mm,0.29 mm,and 0.53 mm in the left/right(L/R),superior/inferior(S/I)and anterior/posterior(A/P)directions,respectively.The measured dynamic accuracy was 0.57 mm and discrepancies measured for the respiratory motion tracking was better than 1mm.The overall positioning accuracy of the system was within 2 mm.Conclusion: The preliminary results from the validation showed great potential to improve the positioning and tracking accuracy in accurate radiation therapy systems,providing an efficient platform for further study of technologies in image guided radiotherapy for motion management during radiotherapy treatment.