4DCT-based treatment plan, 4DCBCT-guided patient setup, and real-time tracking of target motion are essential for accurate stereotactic body radiotherapy (SBRT) of small mobile tumors. However, there is lack of correlation between 4DCT-4DCBCT data in phases of regular respiration cycles and the real-time monitored irregular respiration motion data. We are now proposing a real-time 4D video technique to synchronize respiration patterns in 4DCT, 4DCBCT, and real-time target motion during the dose delivery. Results of feasibility studies with sequential surface images on several patients and volunteers demonstrated the capability of detecting the breathing patterns by the movements of the frontal surfaces of the thorax and abdomen. The deep breathing concurs with larger thorax surface shifts of > 5-mm or tilt angles of > 2-degrees and longer respiratory cycles with periods of >6- seconds. Normal breathing usually has small thorax surface shifts of < 2-mm and angles of < 2-degrees but wide ranges of abdomen surface shifts from 2 to 30-mm and angles from 1 to 5 degrees. At free breathing conditions, we also find that patient respiration cycles and abdomen surface movements are frequently changed with time. More importantly, the personal respiration patterns are predictable with the dynamic volumetric curves determined by the abdomen and thorax surface movements. The surface movements and changes of surface covered volume can be correlated with dynamic volumetric changes in 4DCT and 4DCBCT scans. Thus, the 4D video technique is potentially useful for real-time tracking of small mobile targets in SBRT through synchronization with 4DCT or 4DCBCT.
