Fetal and maternal absorbed dose estimates for positron-emitting tracers

Objectives PET and hybrid (PET/CT and PET/MR) imaging play a pivotal role in clinical diagnosis, staging, treatment planning and surveillance of a number of human diseases. As such, radiation exposure of special patients, such as pregnant women and the fetus, from PET procedures is receiving increasingly attention. Therefore, accurate radiation dose calculation for pregnant patients and embryo/fetus from positron-emitting radiotracers is highly desired.

Methods To obtain representative estimates of the radiation dose to the human body, accurate physical and biological models should be employed. In this work, we evaluate the S-values of 9 positron-emitting radionuclides (C-11, N-13, O-15, F-18, Cu-64, Ga-68, Rb-82, Y-86, and I-124) as well as the absorbed dose and effective dose for 21 positron-emitting labeled radiotracers in realistic voxel-based anthropomorphic computational phantoms of early pregnancy and at 3-, 6-, and 9-months gestation using the most recent biokinetic data of PET radiotracers and the MCNPX general purpose Monte Carlo radiation transport code.

Results The maternal dosimetric aspects for most organs/tissues are less influenced by the gestation, but anatomic changes of the maternal body would increase the effective dose from certain radiotracers. For 18F-FDG, the estimated absorbed doses in the embryo/fetus are 3.05E-02, 2.27E-02, 1.50E-02 and 1.33E-02 mGy/MBq for early pregnancy, 3-, 6- and 9-months gestation, respectively. The absorbed dose from most radiotracers is nonuniformly distributed in the fetus and is almost 1.03-2.0 times higher in the fetal brain than other fetal soft tissues.

Conclusions The produced S-values can be exploited to estimate the radiation dose delivered to pregnant patients and embryo/fetus from various PET radiotracers used in clinical and research settings. The generated dosimetric database using latest generation computational models can be used for the assessment of radiation risks to pregnant woman and embryo/fetus in nuclear imaging procedures. This work also contributes to a better understanding of the distribution of radiation absorbed dose inside the fetus.