¹⁸F-FDG Fetal Dosimetry Calculated with PET/MRI

Area of Science:

• Nuclear Medicine
• Medical Imaging
• Radiological Sciences

Background:

• Assessing fetal absorbed dose from 18F-FDG (fluorodeoxyglucose) is crucial for cancer staging in pregnant women.
• Previous dosimetry studies used PET-only or PET/CT, potentially limiting fetal soft tissue accuracy.
• PET/MRI offers improved soft tissue delineation for more precise fetal dosimetry.

Purpose of the Study:

• To determine the fetal absorbed dose of 18F-FDG in pregnant women undergoing cancer staging.
• To evaluate the utility of PET/MRI for fetal dosimetry in pregnancy.
• To inform clinical decisions regarding the use of 18F-FDG PET during pregnancy.

Main Methods:

• 11 pregnant women (12 scans) with cervical cancer underwent 18F-FDG PET/MRI.
• Fetal activity fraction was determined using MRI-guided region of interest analysis.
• Fetal absorbed doses were calculated using OLINDA/EXM 1.1 with standard organ coefficients and a dynamic bladder model.

Main Results:

• PET/MRI enabled accurate fetal delineation, especially in later pregnancy.
• 18F-FDG uptake varied in the fetus, with higher concentrations in the heart and bladder, and lower in the brain.
• Estimated fetal doses ranged from 2.21E-02 mGy/MBq in early pregnancy to 4.92 ± 1.53 E-03 mGy/MBq in the second trimester.

Conclusions:

• PET/MRI imaging confirms very low fetal absorbed doses from 18F-FDG.
• The findings support the use of clinically indicated 18F-FDG PET scans for cancer staging in pregnant women.
• Pregnancy should not be a contraindication for essential 18F-FDG diagnostic procedures.