To evaluate the accuracy of the system, two radiological technologists with sufficient positioning experience determined the best‐matched position for the bony structures on six parameters between the DR and DRR using the system's manual mode; this position was defined as the reference position. When the reference positions were xref,yref,zref,θx,ref,θy,ref,θz,ref, the error of the system was calculated as the root mean square errors (RMSEs) shown in eqs. (3) and (4). These values were separately calculated in translational and rotational directions. (3)Translation:ΔT=(dx−xref2+dy−yref2+dz−zref2)/3 (4)Rotation:ΔR=(dθx−θx,ref2+dθy−θy,ref2+dθz−θz,ref2)/3