The advent of kilovoltage cone-beam computed tomography (CBCT) integrated with a linear accelerator allows for more accurate image-guided radiotherapy (IGRT). The IGRT technique corrects target displacement based on internal body information obtained by acquiring the CBCT image set and registering it with the simulation CT image set just before the beam is delivered. In the present paper, we compare registration results by CBCT reconstruction quality (either high or medium). We analyzed data from a total of 56 CBCT projections from 6 patients. The translational vector differences were within 1 mm in all but 3 cases. The rotational displacement differences considered components of all three axes, and in 3 of 168 cases (56 projections by 3 axes), showed more than 1 degree of difference.