Hybrid PET/MRI scans safe in pregnant women with cancer, study finds
Japan: Hybrid PET/MR imaging examination in pregnant women poses little risk of exposure to harmful radiation to the fetus, according to a study in the Journal of Nuclear Medicine.
"PET/MRI images of pregnant women injected with 18F-FDG confirmed that the dose of fetal 18F-FDG is very low," Tatsuya Ishiguro, Niigata University Medical & Dental Hospital, Niigata, Japan, and colleagues wrote in their study. "Therefore, clinically appropriate 18F-FDG scans in women with cancer should not be held back because of pregnancy."
When considering the use of PET to stage cancers during pregnancy, the fetal absorbed dose from 18F-FDG administration to the mother is an important piece of information. However, the few existing human case reports were obtained through the either use of PET-only or PET/CT machines. This may not give an accurate identification of the soft tissues of the fetus for dosimetric calculations.
Considering this, Dr. Ishiguro and colleagues in their study presented 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.
Imaging of eleven pregnant women (12 scans) with cervical cancer was done using 18F-FDG PET/MRI. The researchers then retrospectively analyzed the images for the study. The fraction of injected activity concentrated by the fetus was derived from manually drawing regions of interest on the MRI slices.
The fetal time-integrated coefficients were derived and combined with the standard coefficients of the mothers' organs from the ICRP publication 106 from the activity fraction.
The research yielded the following findings:
- 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.
To conclude, clinically appropriate 18F-FDG scans in women with cancer should not be withheld because of pregnancy.
"If the PET scan of a pregnant woman is planned, we encourage nuclear medicine departments to acquire dynamic images," wrote the authors. "These would not increase the radiation dose, but would allow an even more accurate assessment of fetal dosimetry."
Reference:
Paolo Zanotti-Fregonara, Tatsuya Ishiguro, Kosuke Yoshihara, Shiro Ishii, Takayuki Enomoto Journal of Nuclear Medicine Feb 2022, jnumed.121.263561; DOI: 10.2967/jnumed.121.263561
