Interplay effects in PB-PT, can be reduced by generating "time structures" that align to different time-points of the breathing cycle, delivering accurately the pencil beam scanning spots. The main principle here is that partial doses are delivered via PB at different phases of the breathing cycle (the time structures). The partial doses are then accumulated on a reference phase through deformable image registration. The delivery times were provided by the IBA ScanAlgo within the 4D robust plan optimization.