Yuta Matsunaga

This study evaluated fetal-region doses and dose distributions for X-ray pelvimetry (Guthmann and Martius methods) using exposure conditions from a nationwide survey in Japan and compared them with those of a low-dose computed tomography (CT) protocol using a realistic late-pregnancy phantom. A pregnancy model phantom combining an anthropomorphic phantom with a custom-made abdominal phantom was used. Real-time dosimeters were placed at 18 sites across three abdominal levels. The low-dose CT protocol showed a nearly uniform fetal-region dose distribution, whereas the X-ray methods showed heterogeneous distributions depending on beam direction and irradiation field. The reported mean fetal-region doses were 1.16 mGy for Guthmann, 4.05 mGy for Martius, 5.21 mGy for the combined X-ray examinations, and 0.69 mGy for low-dose CT. These results indicate that the low-dose CT protocol evaluated in this study produced a lower fetal-region dose than the Guthmann and Martius methods evaluated in this study.

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.

This study aimed to assess fetal radiation exposure in pregnant women undergoing computed tomography (CT) and rotational angiography (RA) examinations for the diagnosis of pelvic trauma. In addition, this study aimed to compare the dose distributions between the two examinations. Surface and average fetal doses were estimated during CT and RA examinations using a pregnant phantom model and real-time dosemeters. The pregnant model phantom was constructed using an anthropomorphic phantom, and a custom-made abdominal phantom was used to simulate pregnancy. The total average fetal dose received by pregnant women from both CT scans (plain, arterial and equilibrium phases) and a single RA examination was ~60 mGy. Because unnecessary repetition of radiographic examinations, such as CT or conventional 2D angiography can increase the radiation risk, the irradiation range should be limited, if necessary, to reduce overall radiation exposure.