New fetal doses from 18FDG administered during pregnancy: standardization of dose calculations and estimations with voxel-based anthropomorphic phantoms

Objectives Data from the literature show that the fetal absorbed dose from 18F-FDG administration to the pregnant mother ranges from 0.5E-2 to 4E-2 mGy/MBq. These figures were however obtained using different quantification techniques and with basic geometric anthropomorphic phantoms. The aim of this study was to standardize the fetal doses of published as well as new cases and to refine the dose using realistic voxel-based phantoms

Methods The FDG dose to the fetus (n = 19; 5 to 34 weeks of pregnancy) was calculated with OLINDA/EXM 1.1 and OLINDA/EXM 2.0. The image-derived fetal residence time was combined with the standard residence times of the mothers’ organs and the dynamic bladder with 1 h voiding time from the ICRP106 publication. The dose to the uterus was used as a proxy for early pregnancy (up to 10 weeks). The residence times were entered into OLINDA/EXM 1.1, to derive the dose with the classical anthropomorphic phantoms of pregnant women, then into OLINDA/EXM 2.0 to assess the dose using new voxel-based phantoms

Results The average fetal doses (mGy/MBq) with OLINDA/EXM 2.0 were 2.5E-02 in early pregnancy, 1.3E-02 in the late part of first trimester, 8.5E-03 in the second trimester and 5.1E-03 in the third trimester. The differences compared to the doses calculated with OLINDA/EXM 1.1 were +7%, +70%, +35% and -8%, respectively

Conclusions Except in late pregnancy, the doses estimated with realistic voxel-wise anthropomorphic phantoms are higher than the doses derived from old geometric phantoms. The doses remain however well below the threshold for deterministic effects. Thus, pregnancy is not an absolute contraindication of a clinically justified FDG PET scan

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