18F-FDG PET in pregnancy and fetal radiation dose estimates

The purpose of this study was to estimate the fetal radiation exposure resulting from (18)F-FDG PET procedures performed in pregnant patients with malignancies.

Five pregnant patients with a biopsy-proven diagnosis of malignancy who underwent (18)F-FDG PET studies were retrospectively reviewed. All patients underwent PET-only studies (and not PET/CT studies) with a reduced (18)F-FDG dose (except for 1 patient who had a negative pregnancy test immediately before the (18)F-FDG PET procedure but was confirmed to be pregnant a few weeks later), including vigorous hydration and diuresis to minimize radiation exposure to the fetus. One patient underwent (18)F-FDG PET twice during her pregnancy (in the second and third trimesters). Fetal radiation dose was independently assessed for each patient, and an analysis was made of fetal radiation doses using the measurements of activity in the fetuses at various stages of pregnancy.

Six (18)F-FDG PET studies in 5 pregnant patients were analyzed. The (18)F-FDG PET scans were obtained in early pregnancy (n = 1), the second trimester (n = 2), and the third trimester (n = 3). The fetal dose exposure from (18)F-FDG PET studies was estimated to range from 1.1 to 2.43 mGy for various trimesters in pregnancy (except for the patient in the early stage of pregnancy, in whom activity in the whole uterus was considered, and the fetal dose was estimated to be 9.04 mGy). All patients delivered healthy infants with no visible abnormalities at term.

The fetal radiation dose from (18)F-FDG PET studies is quite low and significantly below the threshold dose for deterministic effects due to radiation exposure to the fetus. The estimated fetal radiation exposure in our cases was slightly lower than existing estimates on fetal dose exposure, and as more data become available, the current fetal dose estimates may have to be modified accordingly. By addressing an important safety issue dealing with performing medically necessary (18)F-FDG PET in pregnant patients, these data are expected to help in the imaging workup of cancer patients during pregnancy.