23Na-images of patients treated with 3DCRT or IMRT. Axial orientated, color-encoded 23Na-images (A.1 and B.1) with the corresponding morphological fat-saturated T2-weighted images (A.2 and B.2) of the left kidney. Orientation is given in the images as v = ventral; d = dorsal and the cerebrospinal fluid (CSF) is marked with an asterisk *. The patient shown in A.1/A.2 was treated with IMRT and the other patient in B.1/B.2 respectively with 3DCRT, both after gastric cancer. Though both morphological images present unremarkable renal parenchyma, functional 23Na-images clearly depict a reduced 23Na-content (arrows) in the ventral area included in the field of high-dose radiotherapy.