Fig. 3.

(a) 4D digitally reconstructed radiographs (DRRs) as a function of gantry angle during VMAT delivery on the first day of the four-fraction lung radiotherapy; (b) 4D DRR during VMAT delivery on the second day, (c) on the third day and (d) on the fourth day. Because all the kilovoltage projection images were already sorted into four respiration phase bins to create four CBCT volumes, each gantry angle is related to one of the four CBCT volumes. As a result, respiratory correlated DRR was generated by each CBCT volume at each gantry angle. Prior to the DRR calculation, a clinical target volume (CTV) was added to each CBCT data by physicians delineating the tumor. The MLC field shape and the isocenter are also shown in each DRR image.