Fetal Radiation Dose from ¹⁸F-FDG in Pregnant Patients Imaged with PET, PET/CT, and PET/MR

Abstract

The fetal radiation dose from 18 F-FDG was estimated in a series of pregnant women who underwent a PET scan during a clinical workup for malignancies. Methods: Six pregnant patients were injected with 18 F-FDG (activity range, 296-385 MBq). Three patients were scanned during the first trimester (1 with PET and 2 with PET/CT), 2 were scanned during the second trimester (with PET/MR imaging), and 1 was scanned during the third trimester (with PET). The time-integrated activity coefficients were derived from the fetal radioactivity concentrations measured on the images for all but 1 patient (in early pregnancy [5 wk]), in whom the activity in the uterus was used as a proxy. The coefficients of the mother's organs were derived from standard values (from the International Commission on Radiological Protection). Results: Fetal doses ranged from 6.29E-03 to 2.46E-02 mGy/MBq. An earlier bladder voiding reduced these doses by 25%-45%. The 2 patients who underwent PET/MR imaging-in whom fetal contours could be accurately delineated-displayed the lowest fetal absorbed dose, likely because of more accurate region drawing, with the inclusion of areas of both low and high fetal uptake. Moreover, PET/MR imaging did not necessitate additional radiation for attenuation correction. The placenta, delineated on a PET/MR imaging scan, concentrated 0.27% of the injected activity. Conclusion: Fetal radiation doses are higher in early pregnancy than in late pregnancy, and there can be considerable intersubject variability. However, the total absorbed dose is always well below the threshold for noncancer health effects throughout pregnancy. PET/MR imaging is the optimal PET procedure for imaging pregnant women because it is not associated with radiation for attenuation correction and allows more accurate dosimetric calculations.

New Fetal Dose Estimates from 18F-FDG Administered During Pregnancy: Standardization of Dose Calculations and Estimations with Voxel-Based Anthropomorphic Phantoms

“…In particular, the mother's bladder is the main contributor to the fetal dose from photons, especially in early pregnancy (1,4). In this work, we used the bladder model proposed by ICRP publication 106 and standardized the voiding time at 1 h for all cases.…”

“…Since the publication of monkey data, 2 small series (1,4) and several case reports (5-9) of 18 F-FDG scans of pregnant women have become available in the literature. Although the doses reported in these studies consistently show that the fetal dose is well below the threshold for deterministic effects (10), these doses were obtained with disparate methodologic approaches.…”

“…Although the doses reported in these studies consistently show that the fetal dose is well below the threshold for deterministic effects (10), these doses were obtained with disparate methodologic approaches. For instance, the first cases in early pregnancy were analyzed using a Monte Carlo code and simple geometric models (5,6), whereas in subsequent cases using the dose to the uterus as a proxy was preferred (1,4). Moreover, authors used different assumptions to model the kinetics of the mother's bladder, which is the main contributor to the photon dose to the fetus (1,4).…”

“…For instance, the first cases in early pregnancy were analyzed using a Monte Carlo code and simple geometric models (5,6), whereas in subsequent cases using the dose to the uterus as a proxy was preferred (1,4). Moreover, authors used different assumptions to model the kinetics of the mother's bladder, which is the main contributor to the photon dose to the fetus (1,4). Finally, often the details of the analyses are not fully reported, so that it becomes impossible to reuse the data for further analysis.…”

Development of computational pregnant female and fetus models and assessment of radiation dose from positron-emitting tracers

“…The developed mathematical pregnant female models have been integrated in the MIRDOSE and OLINDA/EXM personal computer software packages for internal dose assessment. They were used by Zanotti-Fregonara et al [10][11][12] and Takalkar et al [13] to estimate the fetal absorbed dose at various gestation periods from 18 F-FDG examinations of pregnant patients. However, mathematical models are commonly used for estimating radiation dose to the embryo/fetus in published literatures [9,14,15] while the organ-level radiation dose of the developing fetus is rarely reported.…”