Absorbed 18F-FDG dose to the fetus during early pregnancy

We describe a rare case of a woman who underwent (18)F-FDG PET/CT during early pregnancy (fetus age, 10 wk). The fetal absorbed dose was calculated by taking into account the (18)F-FDG fetal self-dose, photon dose coming from the maternal tissues, and CT dose received by both mother and fetus.

The patient (weight, 71 kg) had received 296 MBq of (18)F-FDG. Imaging started at 1 h, with unenhanced CT acquisition, followed by PET acquisition. From the standardized uptake value measured in fetal tissues, we calculated the total number of disintegrations per unit of injected activity. Monte Carlo analysis was then used to derive the fetal (18)F-FDG self-dose, including positrons and self-absorbed photons. Photon dose from maternal tissues and CT dose were added to obtain the final dose.

The maximum standardized uptake value in fetal tissues was 4.5. Monte Carlo simulation showed that the fetal self-dose was 3.0 x 10(-2) mGy/MBq (2.7 x 10(-2) mGy/MBq from positrons and 0.3 x 10(-2) mGy/MBq from photons). The estimated photon dose to the fetus from maternal tissues was 1.04 x 10(-2) mGy/MBq. Accordingly, the specific (18)F-FDG dose to the fetus was about 4.0 x 10(-2) mGy/MBq (11.8 mGy in this patient). The CT scan added a further 10 mGy.

The dose to the fetus during early pregnancy can be as high as 4.0 x 10(-2) mGy/MBq of (18)F-FDG. Current dosimetric standards in early pregnancy may need to be revised.