Early first-trimester fetal radiation dose estimation in 16-MDCT without and with automated tube current modulation

OBJECTIVE. The objective of our study was to correlate the estimated fetal absorbed radiation dose derived by directly measured uterine doses in the early first trimester and the volume CT dose index (CTDIvol) for 16-MDCT of the maternal chest, abdomen, and pelvis. MATERIALS AND METHODS. Estimated absorbed fetal dose was measured using a metal oxide semiconductor field effect transistor (MOSFET) dosimeter that was placed in the uterus of an adult female anthropomorphic phantom. The phantom was scanned on a 16-MDCT scanner using three protocols. The scanning parameters for protocol A (trauma) were detector configuration, 16 x 0.625 mm; pitch, 1.75:1; rotation time, 0.5 second; 140 kVp; and 340 mA. The scanning parameters for protocol B (CT angiography) were detector configuration, 16 x 1.25 mm; pitch, 1.38:1; rotation time, 0.6 second; 140 kVp; and 300 mA. The scanning parameters for protocol C, which is the automated tube current modulation (ATCM) protocol previously used in the literature, were detector configuration, 16 x 1.25 mm; pitch, 0.938:1; rotation time, 0.5 second; 140 kVp; and 380 mA. The protocols were also modified for the ATCM mode; the CTDIvol was documented from the scanner's console. Correlation between these data was tested with a goodness-of-fit model. RESULTS. Absorbed fetal radiation dose in the early first trimester correlated with the CTDIvol via a linear regression equation. For a constant tube current and peak voltage of 140 kVp, fetal dose (mGy) = 1.665 x CTDIvol (mGy) - 7.059. For the ATCM mode and a constant kVp of 140, fetal dose (mGy) = 2.151 x CTDIvol (mGy) - 2.200. The goodness of fit (R-2) for the equations is 0.99 and 0.91, respectively. CONCLUSION. In both the manual and ATCM modes, absorbed fetal radiation dose can be estimated from the CTDIvol obtained at the time of scanning independent of pitch and tube current - time product (mAs).