An approach to assess target dose homogeneity of interplay effects in PB-PT for daily adaptive PT. A log-based 4D reconstruction and accumulation from daily breathing pattern records, treatment delivery log files, and weekly repeated 4D-CTs, enabled the clinical evaluation of interplay and motion effects. Reconstruction of the 4D dose distribution did not reveal any loss of target dose homogeneity suggesting that potential dose degradation can be succesfully evaluated, and trigger treatment adaptation where necessary.