Biodistribution and radiation dosimetry of [(11)C]choline: a comparison between rat and human data.

Purpose: Methyl-(11)C-choline ([(11)C]choline) is a radiopharmaceutical used for oncological PET studies. We investigated the biodistribution and biokinetics of [(11)C]choline and provide estimates of radiation doses in humans.

Methods: The distribution of [(11)C]choline was evaluated ex vivo in healthy rats (n=9) by measuring the radioactivity of excised organs, and in vivo in tumour-bearing rats (n=4) by PET. In addition to estimates of human radiation doses extrapolated from rat data, more accurate human radiation doses were calculated on the basis of PET imaging of patients with rheumatoid arthritis (n=6) primarily participating in a synovitis imaging project with [(11)C]choline. Dynamic data were acquired from the thorax and abdomen after injection of 423+/-11 MBq (mean+/-SD) of tracer. Following PET imaging, the radioactivity in voided urine was measured. The experimental human data were used for residence time estimations. Radiation doses were calculated with OLINDA/EXM.

Results: In rats, the radioactivity distributed mainly to the kidneys, lungs, liver and adrenal gland. The effective dose in a human adult of about 70 kg was 0.0044 mSv/MBq, which is equivalent to 2.0 mSv from 460 MBq of [(11)C]choline PET. The highest absorbed doses in humans were 0.021 mGy/MBq in the kidneys, 0.020 mGy/MBq in the liver and 0.029 mGy/MBq in the pancreas. Only 2.0% of injected radioactivity was excreted in the urine during the 1.5 h after injection.

Conclusion: The absorbed radiation doses after administration of 460 MBq of [(11)C]choline were low. Except for the pancreas, biodistribution in the rat was in accordance with that in humans, but rat data may underestimate the effective dose, suggesting that clinical measurements are needed for a more detailed estimation. The observed effective doses suggest the feasibility of [(11)C]choline PET for human studies.