Biodistribution and radiation dosimetry of the dopamine D2 ligand 11C-raclopride determined from human whole-body PET

Whole-body radiation dosimetry of C-11-raclopride was performed in healthy human volunteers. Methods: Subjects (n = 6) were scanned with PET. Subjects received single-bolus injections of C-11-raclopride (S-(-)-3,5-dichloro-N-[(1-ethyl-2-pyrrolidinyl)]methyl-2-hydroxy-6-methoxybenzamide) (533 +/- 104 MBq) and were scanned for approximately 110 min with a 2-dimensional whole-body protocol. Regions of interest were placed over all visually identifiable organs and time-activity curves were generated. Residence times were computed as the area under the curve of the time-activity curves, normalized to injected activities and standard values of organ volumes. Absorbed doses were computed according to the MIRD schema with MIRDOSE3.1 software. Results: Organs with the highest radiation burden were gallbladder wall, small intestine, liver, and urinary bladder wall. Conclusion: On the basis of the estimated absorbed dose, the maximum allowable single study dose under U.S. federal regulations for studies performed under Radiation Drug Research Committee is 1.58 GBq (42.8 mCi). This is still considerably higher than the doses of C-11-raclopride commonly used in research PET (370-555 MBq).