We would like to thank the faculty, staff and residents of the Duke University Medical Center Department of Radiology, whose interest in the topic of fetal exposures to diagnostic procedures was the impetus for summarizing this material in an "on-line" format.
Fetal Doses From Nuclear Medicine Studies: The fetal dose estimations presented here are based on the work of Joy Russell, Richard Sparks, Michael Stabin and Richard Toohey1 of the Radiation Internal Dose Information Center, Oak Ridge Associated Universities. Because it is not practical to directly measure radiation doses to the fetus in a given individual, they must be calculated. These complex computations are based on "phantoms", which are mathematical simulations of average human geometries. For this reason, they cannot be strictly applied to any individual. In addition, the nature of the "Monte Carlo" calculations used to produce the estimates can lead to significant errors in the case of small organs or tissues. Finally, the fetal dose depends on the amount of administered radioactivity for a given study. There is considerable variation the amount of administered radioactivity in actual practice. In view of these limitations, these estimates of fetal radiation dose should be treated as exactly that: estimates.
Fetal Doses From Plain Film and Fluoroscopic Procedures: These doses were computed by the author. For plain films, data from the NEXT study2 were used to estimate skin entrance exposures for selected procedures. Published tables which convert skin entrance exposure to deep organ dose3 were then applied to estimate dose to the uterus, which is about the same as the fetal dose during early gestation. For this reason, these estimates cannot be strictly applied to a late term fetus. In addition, all the limitations outlined above for nuclear medicine computations apply to the plain film calculations. Similar methods were used for fluoroscopic procedures. The fluoroscopy estimates have additional uncertainty because the studies are highly operator-dependent. For this reason, they should be viewed as "order-of-magnitude" estimates only.
Fetal Doses From CT Procedures: Very little information is available for fetal doses from CT studies. For procedures in which the fetus is within the primary beam, the tabulated estimates are based on the "CT Dose Index" (CTDI). For procedures in which the fetus is not included within the primary field, the dose is likely only a small ( < 1 %) fraction of the CTDI. As for fluoroscopic studies, these are "order-of-magnitude" estimates.
Radiation Risk Assessment -- Dr. Robert Brent of Thomas Jefferson University has assembled extensive material and experience relevant to the evaluation of fetal radiation risk. It appears in:
Brent RL. Developmental and Reproductive Risks of Radiological Procedures Utilizing Ionizing Radiation During Pregnancy. In: Radiation Protection in Medicine: Contemporary Issues. Proceedings of the Thirty-Fifth Annual Meeting of the National Council on Radiation Protection and Measurements.Arlington: NCRP, 1999.