Fig. 1

Exemplary sagittal dose distributions of the reference plan on the planning CT (a), of the ART3 plan on the synthetic CT (sCT) (b) and of the IGRT plan on the sCT (c). Dose difference maps between the IGRT approach and the three adaptive approaches on the sCT (d–f) revealed anatomical regions in the rectum, bladder and soft tissue with dose differences of up to 8 Gy. Prescription doses were D(CTV) = 40 Gy and D(PTV) = 36.25 Gy. A low dose threshold of 1% was used for the dose difference maps