In order to be able to use the antibody Girentuximab in positron emission tomography (PET), it was radioactively labelled with Iodine-124. REDECTANE® binds to the antigen CA IX and will accumulate in the tumour tissue. An uptake of this antibody in tumour tissue can be visualised by PET. Additional information provided by CT can be used to localise accumulation of the antibody. PET/CT generally has a higher resolution than CT alone.