Fetal radiation dose in computed tomography.

The connection between recorded volumetric CT dose index (CTDIvol) and determined mean fetal dose (D-f) was examined from metal-oxide-semiconductor field-effect transistor dose measurements on an anthropomorphic female phantom in four stages of pregnancy in a 64-slice CT scanner. Automated tube current modulation kept the mean D-f fairly constant through all pregnancy stages in trauma (4.4-4.9 mGy) and abdomino-pelvic (2.1-2.4 mGy) protocols. In pulmonary angiography protocol, the mean D-f increased exponentially as the distance from the end of the scan range decreased (0.01-0.09 mGy). For trauma protocol, the relative mean D-f as a function of gestational age were in the range 0.80-0.97 compared with the mean CTDIvol. For abdominopelvic protocol, the relative mean D-f was 0.57-0.79 and for pulmonary angiography protocol, 0.01-0.05 compared with the mean CTDIvol, respectively. In conclusion, if the fetus is in the primary beam, the CTDIvol can be used as an upper estimate of the fetal dose. If the fetus is not in the primary beam, the fetal dose can be estimated by considering also the distance of the fetus from the scan range.