Fetal Dosimetry at CT: A Primer

CT scanning of a pregnant patient is often a source of distress for both patient and staff. Despite having expertise in image interpretation, a radiologist may not feel equipped to discuss the radiation-related safety issues during CT scanning of the fetus. In addition, patients are frequently concerned about the risk of adverse effects on the fetus from exposure to ionizing radiation. Recognizing the possibility of adverse effects from fetal exposure and the impossibility of direct in vivo measurement, medical physicists have developed several methods to estimate the amount of radiation reaching the fetus. A physician should know the potential biologic effects of fetal irradiation and at what radiation dose thresholds they occur. Physicians should also have an understanding of these methods and how the numbers they produce relate to potential fetal bioeffects. Furthermore, radiologists should have some understanding of how a qualified medical physicist calculates the fetal dose, how much they should trust those numbers, and the relevant variables that can affect the outcomes. Finally, the radiologist should know the magnitude of doses for CT scans commonly used in pregnant patients. Armed with this knowledge, a radiologist should be confident when discussing fetal dose and determining the best course of action for the pregnant patient. Online supplemental material is available for this article. ^©RSNA, 2020.