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Early First Trimester Fetal Dose Estimation Method in a Multivendor Study of 16- and 64-MDCT Scanners and Low-Dose Imaging Protocols

¹ Department of Radiology, Duke University Medical Center, Erwin Rd., Box 3808, Durham, NC 27710.
² Department of Occupational and Environmental Safety Office, Radiation Safety Division, Duke University Medical Center, Durham, NC.
³ Siemens Healthcare, CSG Solutions, Cary, NC.

OBJECTIVE. The purpose of this study was to corroborate the relation between the estimated absorbed fetal dose derived from directly measured uterine doses early in the first trimester and the volume CT dose index (CTDI_vol) for 16- and 64-MDCT of the maternal chest, abdomen, and pelvis.

MATERIALS AND METHODS. Estimated absorbed fetal dose was measured with a metal oxide semiconductor field effect transistor (MOSFET) dosimeter placed in the expected uterine location in an anthropomorphic phantom of a woman and scanned with 16- and 64-MDCT units of one vendor and a 64-MDCT unit of another vendor. A trauma chest, abdomen, and pelvis protocol and an abdomen and pelvis protocol were used. Absorbed uterine dose was measured directly from the MOSFET detector. The CTDI_vol for each protocol was recorded from the scanner console. Correlation between mean uterine dose and CTDI_vol was tested with a goodness of fit model.

RESULTS. The absorbed uterine dose ranged from 9.25 to 37.7 mGy. Absorbed fetal dose in the early first trimester correlated with CTDI_vol in a linear regression equation. For the 16-MDCT scanner, at 130 kVp, the fetal dose was 2.091 x CTDI_vol – 9.489. For the 64-MDCT scanner from the same vendor, at 120 kVp, the fetal dose was 1.113 x CTDI_vol + 1.773. For the 64-MDCT scanner from the other vendor, at 120 kVp, the fetal dose was 1.378 x CTDI_vol – 1.014. The goodness of fit results (R²) for the equations were 0.97, 0.98, and 0.99.

CONCLUSION. Estimated absorbed fetal dose during the first trimester of pregnancy is linearly associated with CTDI_vol regardless of beam energy, detector configuration, and scanner manufacturer.

Keywords: CT dosimetry • fetal dose • pregnancy

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