Image fusion of CT-data set with the accumulated 3-D dosimetry of three different irradiation sessions. (a) Contrast-enhanced CT after first (No.1) CT-guided positioning of brachytherapy catheters (long arrow) in metastases of a colorectal carcinoma. The short arrow shows the 3-D dosimetry of another lesion, irradiated in session No.2. (b) Contrast-enhanced CT after third intervention (No.3) in the same patient. The arrow shows the upper boundary of the 3-D dosimetry of the lesion irradiated in session No.2. Physical doses are shown in the colour map.