JNM: Fetal radiation exposure low in PET studies
Researchers found low fetal radiation exposures in a retrospective study assessing the effects of F-FDG PET studies performed on pregnant patients with cancer, according to findings published in the July issue of the Journal of Nuclear Medicine.

Amol M. Takalkar, MD, of the PET Imaging Center, Biomedical Research Foundation of Northwest Louisiana, Shreveport, La., and colleagues reviewed six F-FDG PET studies on five pregnant women with malignancies to assess fetal radiation doses. Study authors found that the doses were significantly below the threshold for deterministic effects of radiation exposure to the fetus, and all patients ultimately delivered healthy infants without visible abnormalities.

Takalkar and colleagues noted a lack of data on fetal radiation exposure and dosimetry in pregnant patients undergoing F-FDG PET exams.

“To our knowledge, this is the first and largest series of pregnant patients for whom fetal radiation exposure from F-FDG PET was calculated. Our data add considerably to the existing literature about fetal radiation exposure from F-FDG PET studies of pregnant patients,” wrote Takalkar et al.

In their retrospective study, each of the five patients—ranging in age from 22 to 37—was proven to have cancer and was counseled prior about the risks of the PET scan. Two patients had cervical cancer, two had lymphoma and one had lung cancer. They underwent PET-only scans—not PET/CT scans—and four of the five patients were administered smaller doses of F-FDG than the standard protocol, due to their pregnancies. One patient tested negative for pregnancy prior to the study and was given a standard dose, but was later found to be pregnant at the time of the scan. Adequate hydration was standard protocol for each procedure.

Fetal radiation dose was independently assessed for each patient, and an analysis was conducted using measurements of activity in the fetuses at various stages of the pregnancies, combined with data for the standard metabolism of F-FDG. For one patient that underwent an early PET scan, the radiopharmaceutical activity was noted in the uterine region.

For all other patients, the fetus was clearly delineated with F-FDG uptake. The radiopharmaceutical was found in the fetal myocardium with mostly faint background activity in the remaining parts of the fetus. There was no prominent activity in other fetal regions, according to the study.

“Fetal radiation exposure resulting from medical imaging may be a frightening and complicated issue for pregnant women to understand in the course of granting their consent for an imaging procedure,” Takalkar et al wrote. “Lack of accurate, scientific data about the risks and benefits of F-FDG PET in diseased pregnant patients combined with medical liability concerns may result in a conservative and potentially inappropriate choice to withhold necessary medical imaging in such situations.”

Study authors concluded that although radiation exposure from the procedure is low, efforts should be made to minimize radiation exposure.