The data presented demonstrate that AlignRT system provides a reproducible setup throughout treatment, with typical breath‐hold motions of <1 mm. The dosimetric consequences of these subtle breath‐hold motions are similarly small. Gierga et al. (15) performed a similar study and noted delivered and planned breath‐hold positions typically to have means around 2 mm in each direction. We used ±3 mm and ± 3° as the RTD tolerance, and the Gierga study used ±5 mm (no rotational tolerance was reported). We have simulated the motion using mean RTDs from the Gierga study, 1.0 mm SD, and their tolerance to estimate corresponding dosimetric effect. A patient (with IMN) with average motion was selected. RTDs of (2.2 mm±1.0 mm, 2.3 mm±1.0 mm, 2.0 mm±1.0 mm) and tolerance of ±5 mm were generated (0° rotational motion was used as it was not reported in the Gierga study). Delivered dose was estimated the same way in this study. In more detail, 200 entries of RTDs were simulated using the means and standard deviations listed above. Each RTD entry corresponds to an isocenter shift, and each isocenter shift results a deviated dose distribution. The final dose distribution was an equal‐weighted average of all 200 varied ones. The same orientation system shown in Fig. 1 was used for this simulation (i.e., 2.2 mm, −0.5 mm, 1 mm), which means that the isocenter moved posterior 2.2 mm, left 0.5 mm, and superior 1 mm. The estimated heart mean dose using ±5 mm tolerance was 110 cGy, the estimate using ±3 mm tolerance on the same patient was 106 cGy, and the planned dose was 97 cGy; the lungs V20 were 7.74%, 7.72%, and 6.66%; the corresponding IMN mean doses were 4983 cGy, 4970 cGy, and 4958 cGy; the corresponding IMN 40 Gy coverage were 100%, 100%, and 100%. It appears that, by increasing the tolerance, the average motion was increased as well, and it might result in slightly higher delivered heart mean dose, lungs V20, and IMN dose. A thorough study is needed to make meaningful conclusion.