Radiation Absorbed Dose to the Embryo and Fetus from Radiopharmaceuticals.

Nuclear medicine procedures are generally avoided during pregnancy out of concern for the radiation dose to the fetus. However, for clinical reasons, radiopharmaceuticals must occasionally be administered to pregnant women. The procedures most likely to be performed voluntarily during pregnancy are lung scans to diagnose pulmonary embolism and 18F-fluoro-2-deoxyglucose (18F-FDG) scans for the staging of cancers. This article focuses on the challenges of fetal dose calculation after administering radiopharmaceuticals to pregnant women. In particular, estimation of the fetal dose is hampered by the lack of fetal biokinetic data of good quality and is subject to the variability associated with methodological choices in dose calculations, such as the use of various anthropomorphic phantoms and modeling of the maternal bladder. Despite these sources of uncertainty, the fetal dose can be reasonably calculated within a range that is able to inform clinical decisions. Current dose estimates suggest that clinically justified nuclear medicine procedures should be performed even during pregnancy because the clinical benefits for the mother and the fetus outweigh the small and purely hypothetical radiation risk to the fetus. In addition, the fetal radiation dose should be minimized without compromising image quality, such as by encouraging bladder voiding and by using positron emission tomography (PET)/magnetic resonance imaging (MRI) devices or high-sensitivity PET scanners that generate images of good quality with a lower injected activity.