Details of the AlignRT beam hold system have been reported. 17 , 18 , 19 Briefly, the AlignRT beam hold system consists of three ceiling‐mounted camera pods that work together to generate a 3D surface image of the patient. To set up and track patients, the system needs a reference image and a verification image. The CT skin rendering was our default reference image. Actual patient's surface was used as reference when bolus was needed for the treatment. The accuracy of the patient's surface capture was verified by port films. The system registers each verification image to the reference to determine, in real time, the differences between the reference and verification images, including three translational and three rotational displacements — the Real Time Deltas (RTD). For a given patient, the RTDs were calculated against the same reference image for the entire treatment. In other words, RTDs were absolute displacements to the same surface. Automatic gating was implemented. Tolerance levels are set (for permitted differences between the reference and verification images) for the radiation beam to be turned “on” automatically. For most patients, ±3 mm and ± 3° were used for the translational and rotational differences, respectively.