¹⁸F-FDG Fetal Dosimetry Calculated with PET/MRI

Abstract

The fetal absorbed dose from ¹⁸F-FDG administration to the mother is an essential piece of information when considering the use of PET to stage cancers during pregnancy. However, the few existing human case reports were obtained using either PET-only or PET/CT machines, which may not accurately identify the soft tissues of the fetus for dosimetric calculations. This study presents data from 11 women injected with ¹⁸F-FDG for cancer staging during the first two trimesters of pregnancy and is the first to be entirely acquired with PET/MRI. <b>Methods:</b> Eleven pregnant women (12 scans) with cervical cancer were imaged with ¹⁸F-FDG PET/MRI, and their images were retrospectively analyzed for this study. The fraction of injected activity concentrated by the fetus was derived from manually drawing regions of interest on the MRI slices. From the activity fraction, the fetal time-integrated coefficients were derived and combined with the standard coefficients of the mothers’ organs from the ICRP publication 106. The fetal absorbed doses were calculated with OLINDA/EXM 1.1 and a dynamic bladder model. <b>Results:</b> All fetuses after early pregnancy could be accurately delineated due to the coregistered MRI scans. ¹⁸F-FDG activity was unevenly distributed in the fetal body: the hearts and the urinary bladders were generally visible, while the brain showed lower uptake. The estimated fetal doses were 2.21E-02 mGy/MBq for one woman imaged in early pregnancy, 7.38 ± 0.25 E-03 mGy/MBq for three women imaged at the end of the first trimester, and 4.92 ± 1.53 E-03 mGy/MBq for eight women imaged during the second trimester. <b>Conclusion:</b> PET/MRI images of pregnant women injected with ¹⁸F-FDG confirm that the fetal ¹⁸F-FDG dose is very low. Therefore, clinically appropriate ¹⁸F-FDG scans in women with cancer should not be withheld because of pregnancy.

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