Estimation of the beta+ dose to the embryo resulting from 18F-FDG administration during early pregnancy

Although 18F-FDG examinations are widely used, data are lacking on the dose to human embryo tissues in cases of exposure in early pregnancy. Although the photon component can easily be estimated from available data on the pharmacokinetics of 18F-FDG in female organs and from phantom measurements (considering the uterus as the target organ), the intensity of embryo tissue uptake, which is essential for deriving the beta+ dose, is not known. We report the case of a patient who underwent 18F-FDG PET/CT for tumor surveillance and who was later found to have been pregnant at the time of the examination (embryo age, 8 wk).

The patient received 320 MBq of (18)F-FDG. Imaging started with an unenhanced CT scan 1 h after the injection, followed by PET acquisition. PET images were used to compute the total number of beta+ emissions in embryo tissues per unit of injected activity, from standardized uptake value (SUV) measurements corrected for partial-volume effects. A Monte Carlo track structure code was then used to derive the beta+ self-dose and the beta+ cross-dose from amniotic fluid. The photon and CT doses were added to obtain the final dose received by the embryo.

The mean SUV in embryo tissues was 2.7, after correction for the partial-volume effect. The mean corrected SUV of amniotic fluid was 1.1. Monte Carlo simulation showed that the beta+ dose to the embryo (self-dose plus cross-dose from amniotic fluid) was 1.8E-2 mGy per MBq of injected 18F-FDG. Based on MIRD data for the photon dose to the uterus, the estimated photon dose to the embryo was 1.5E-2 mGy/MBq. Thus, the specific 18F-FDG dose to the embryo was 3.3E-2 mGy/MBq (10.6 mGy in this patient). The CT scan added a further 8.3 mGy.

The dose to the embryo is 3.3E-2 mGy/MBq of 18F-FDG. The beta+ dose contributes 55% of the total dose. This value is higher than previous estimates in late nonhuman-primate pregnancies.