Fetal dose estimates for (18)F-fluoro-L-thymidine using a pregnant monkey model.

Abstract

Estimating the radiation dose received by the fetus from nuclear medicine procedures is important because of the greater sensitivity of rapidly developing fetal tissues to ionizing radiation. (18)F-fluoro-L-thymidine (FLT) uptake is related to cellular proliferation and is currently used to monitor tumor progression and response to therapy. This study was undertaken to estimate-on the basis of biodistribution data obtained by PET/CT in pregnant rhesus monkeys-radiation absorbed dose to a human fetus administered (18)F-FLT. Three pregnant rhesus macaques (gestational age, 113 +/- 8 d) were administered (18)F-FLT and imaged for 2 h on a PET/CT scanner. Time-activity curves for maternal and fetal organs were generated in anatomic regions of interest identified via CT. Doses were estimated using OLINDA/EXM and the 6-mo-pregnant human model. The extrapolated whole-body maternal dose obtained, 11.4 microGy/MBq, is similar to the previously reported adult female dose of 15.6 microGy/MBq. The estimated total-body dose to a human fetus is 24 microGy/MBq. Significant long-term (18)F-FLT accumulation in fetal liver resulted in a fetal liver dose of 53 microGy/MBq. The fetal dose estimate in a 6-mo-pregnant human using (18)F-FLT is slightly greater than that reported for (18)F-FDG. (18)F-FLT trapping in the fetal liver should be considered in the risk-benefit analysis of (18)F-FLT PET examination in pregnant patients.