Dosimetry of iodine-123 iodobenzamide in healthy volunteers.

The distribution of the dopamine D2-receptor specific ligand iodine-123 (S)-(-)-2-hydroxy-3-iodo-6-methoxy-N[(1-ethyl-2- pyrrolidinyl)methyl]-benzamide (123I-IBZM) was investigated in human adults from whole-body scans, blood samples and urine collected up to 48 h after injection. Results from the present study performed in six healthy volunteers were combined with those of five volunteers from a previous study. Using the brain, liver, lungs and spleen as source organs, the MIRD method was applied to calculate the absorbed radiation dose of the radioligand in various organs. The thyroid (despite blockage), gallbladder wall, large intestinal walls and spleen received the highest absorbed doses. The average effective dose equivalent of 123I-IBZM for adults was estimated to be 0.034 mSv/MBq. The absorbed dose to the thyroid may be a limiting factor for 123I-IBZM studies in children.