Development and validation of a pregnant phantom with adjustable fetal presentation for region-specific fetal radiation dose assessment during pelvic radiography.

BACKGROUND: Accurate assessment of fetal radiation dose during diagnostic X-ray examinations remains challenging because commercially available pregnancy phantoms do not adequately reproduce fetal anatomy or permit organ-specific dose measurements.

PURPOSE: The purpose of this study was to develop a pregnant phantom with adjustable fetal presentation and to evaluate its anatomical realism and applicability for fetal dose assessment during pelvic radiography.

METHODS: The developed phantom comprised an anthropomorphic phantom, a whole-body fetal phantom, acrylic components, and water-filled plastic bags. The fetal phantom was fabricated using three-dimensional printing technology and incorporated bone-equivalent and soft-tissue-equivalent materials. Fetal presentations could be adjusted to cephalic or breech presentations by repositioning the fetal phantom within the abdominal phantom. Computed tomography (CT) images were acquired to measure CT numbers of the fetal brain, thorax, abdomen, pelvic bone, and surrounding water-filled regions. Absorbed doses were measured using real-time dosimeters placed at five locations in the fetal head and three locations in the fetal abdomen. Dose measurements were performed during pelvic radiography and compared with those obtained using a conventional homogeneous pregnancy phantom.

RESULTS: The mean CT numbers of the fetal brain, thorax, abdomen, pelvic bone, and water-filled regions were 2.1, -0.8, -0.4, 323.8, and 1.6 HU, respectively. These values were within the expected ranges for soft tissue and bone and were comparable to those of a conventional homogeneous phantom. During pelvic radiography, the mean absorbed doses measured using the adjustable fetal-presentation phantom were 1.34 mGy in the fetal head and 0.07 mGy in the fetal abdomen for the cephalic presentation, and 0.05 mGy and 1.67 mGy, respectively, for the breech presentation. In comparison, the mean absorbed dose measured in the fetal region of the conventional homogeneous phantom was 2.05 mGy. The findings demonstrated substantial differences in regional fetal dose distribution according to fetal presentation. In particular, the fetal head dose in the cephalic presentation was lower than that measured using the conventional phantom. This difference may be partly attributable to attenuation by the fetal skull; however, the comparison should be interpreted with caution given differences in phantom geometry, internal materials, and dosimeter locations between the two phantoms.

CONCLUSION: A novel pregnant phantom with adjustable fetal presentation was successfully developed. The phantom reproduced anatomically relevant structures using realistic bone-equivalent and soft-tissue-equivalent materials and enabled direct dose measurements in specific fetal anatomical regions. Compared with a conventional homogeneous phantom, the developed phantom provided a more detailed assessment of fetal dose distributions and allowed evaluation of the effects of fetal presentation on radiation exposure during pelvic radiography.