INTERESTING IMAGE
Title: FDG PET/CT of a Late-term Pregnant Woman With Breast Cancer
Authors: Te-Chun Hsieh, MD,*† Yu-Chin Wu, MD,‡ Shung-Shung Sun, MD,*†
Lu-Yen Chu, MD,*§ Kuo-Yang Yen, BS,*† and Chia-Hung Kao, MD*¶
Abstract: A 38-year-old pregnant woman at 26-week gestation with left breast cancer
requested an FDG PET/CT scan for more detailed staging of her breast cancer before
treatment. After discussing the potential radiation-related risk and estimating possible
absorbed dose to fetus, she consented for examination. By using a low-radiation-dose CT
protocol and administration of routine 370-MBq FDG without diuresis, the resultant
calculated (using existing models to predict fetal radiation exposure) fetal dose from CT
and FDG would be 3.60 mGy and 6.29 mGy, respectively. In contrast to the existing few
literatures, our case also demonstrated previously unreported uptake in the fetal kidneys.
Key Words: breast cancer, pregnancy, fetus, FDG PET/CT, radiation exposure, kidney
From the *Department of Nuclear Medicine and PET Center, China Medical University
Hospital, Taichung, Taiwan; †Department of Biomedical Imaging and Radiological
Science, China Medical University, Taichung, Taiwan; ‡Departmentof Nuclear Medicine,
National Taiwan University Hospital Hsin-Chu Branch, Hsinchu City, Taiwan; §China
Medical University, Taichung, Taiwan; and ¶School of Medicine, China Medical
University, Taichung, Taiwan.
Y-C.W. and C-H.K. contributed equally to this work.
Conflicts of interest and sources of funding: none declared.
Reprints: Chia-Hung Kao, MD, Department of Nuclear Medicine and PET Center, China
Medical University Hospital, No. 2, Yuh-Der Rd, Taichung 404, Taiwan. E-mail:
d10040@mail.cmuh.org.tw.
FIGURE 1. A 38-year-old pregnant woman at 26-week gestation with left breast cancer
was demonstrated by PET/CT performed for staging (T2N0M0, stage IIA). The patient
requested FDG PET/CT for her breast cancer. Because estimated fetal dose was unlikely
over 50 mGy, deterministic effect of ionizing radiation would not happen with nearly
negligible increases of incidence of childhood cancers.1–3 Therefore, interruption of
pregnancy seemed unnecessary.4 After realizing these facts about ionizing radiation, she
consented for examination. The patient received intravenous injection of 370-MBq FDG
with 500-mL 0.9% saline. She was asked to void before scanning, 60 minutes after
injection. Certain procedures, such as encouraging frequent voiding and use of diuretics
that helped to decrease radiation burden,5 were not applied because of the concern of
affecting image quality. PET/CT scanned from head to midthighs with low-radiation-dose
CT protocol (0.8-second rotation time, 120 kVp, variable mA with AutomA technique,
3.75-mm slice thickness, and 1.75:1 pitch). Reconstructed images and transaxial slices
were provided to demonstrate complex orientations between mother and fetus. Four
representative obliquely sectioned images (C, left to right) were as follows: maximum
intensity projection (MIP) of CT revealing skeleton of mother and fetus, thin-sectioned
CT showing maternal breast cancer and fetus simultaneously, MIP of PET revealing FDG
radioactivity in breast cancer and fetus, and fused MIP PET/CT. Consecutive transaxial
slices (D) indicated FDG radioactivity in the fetal heart (white arrows) and kidneys
(black arrows). Slight misregistration of PET/CT was observed, probably caused by
intrauterine fetal movement. Inconspicuous fetal brain uptake (B, black arrowhead) was
also noted. Nevertheless, there were also maternal breast cancer (A, white arrowhead),
cold-activated brown adipose tissues in the neck, and absence of metastases. Estimated
fetal dose from FDG was 6.29 mGy derived from conservative fetal dose conversion
factor for 6-month gestation (1.7×10-2 mGy/MBq).6 CT dose was 3.60 mGy derived from
CT dose index (CTDIvol) of uterus (3.0 mGy) and conservative conversion factor from
the CTDIvol to fetal dose (1.2 mGy/mGy).7 Finally, a healthy male baby was delivered
uneventfully after full-term pregnancy. Breast cancer during pregnancy is uncommon8 –13
and can cause difficulties in diagnosis and treatment with ionizing radiation and
chemotherapy in consideration of fetal effect. To date, there are still debates about fetal
doses from maternal FDG administration.5,6,14 Despite drawback of PET/CT increasing
fetal dose from CT, simultaneous visualization of fetal anatomic and physiological details
contributes to discover the previously never reported fetal renal accumulation of FDG in
our case.
Theoretically, such finding is expectable because fetal urine production begins between 8
and 10 weeks’ gestation.15 A threshold of 100 –200 mGy is needed to cause fetal mental
retardation and organ malformations.16 Besides, stochastic effects causing cancer or germ
cell mutation may increase above 50 mGy.2 Because average absorbed dose to fetus from
single diagnostic study is much less than 50 mGy, fear of fetal radiation exposure should
not hamper examinations’ benefit to maternal health.1,17–24 However, safety counseling is
necessary before radiation exposure. Informed consent should also be obtained before
examination. Nonionizing imaging procedures should always be considered in priority
for pregnant patients.2
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