Biodistribution and radiation dosimetry of the amyloid imaging agent 11C-PIB in humans.

UNLABELLED: We investigated the biodistribution and radiation dosimetry of the PET amyloid imaging agent (11)C-PIB ((11)C-6-OH-BTA-1) (where BTA is benzothiazole) in humans. Previous radiation exposure estimates have been based on animal experiments. A dosimetry study in humans is essential for a balanced risk-benefit assessment of (11)C-PIB PET studies.

METHODS: We used data from 16 different (11)C-PIB PET scans on healthy volunteers to estimate radiation exposure. Six of these scans were dynamic imaging over the abdominal region: 3 covering the upper abdomen and 3 covering the middle abdomen. On average, 489 MBq of (11)C-PIB (range, 416-606 MBq) were injected intravenously, and dynamic emission scans were recorded for up to 40 min. Two subjects had whole-body imaging over the entire body to illustrate the biodistribution. PET brain scans and blood and urine radioactivity measurements from our previous (11)C-PIB studies were also analyzed. Thirteen source organs and the remainder of the body were studied to estimate residence times and mean radiation-absorbed doses. The MIRD method was used to calculate the radiation exposure of selected target organs and the body as a whole.

RESULTS: There is a high degree of consistency between our human data and previous biodistribution information based on baboons. In our study, the highest radiation-absorbed doses were received by the gallbladder wall (41.5 microGy/MBq), liver (19.0 microGy/MBq), urinary bladder wall (16.6 microGy/MBq), kidneys (12.6 microGy/MBq), and upper large intestine wall (9.0 microGy/MBq). The hepatobiliary and renal systems were the major routes of clearance and excretion, with approximately 20% of the injected radioactivity being excreted into urine. The effective radiation dose was 4.74 microSv/MBq.

CONCLUSION: The established clinical dose of (11)C-PIB required for 3-dimensional PET amyloid imaging has an acceptable effective radiation dose. This dose is comparable with the average exposure expected in other PET brain receptor tracer studies. (11)C-PIB is rapidly cleared from the body, largely by the kidneys. From the viewpoint of radiation safety, these results support the use of (11)C-PIB in clinical PET studies.