# Evaluation of Radiation Dose and Image Quality in the Transition from Conventional Pelvimetry to Low-Dose Helical CT Pelvimetry

## TL;DR

Low-dose CT pelvimetry significantly reduces radiation exposure compared to traditional X-rays while providing sufficient image quality for diagnosis.

## Contribution

Demonstrated that low-dose CT pelvimetry reduces radiation dose by up to 75% compared to conventional methods without compromising diagnostic quality.

## Key findings

- Low-dose CT reduced pelvic radiation dose by 50% and fetal dose by 40% compared to conventional pelvimetry.
- CT provided more homogeneous dose distribution and no repeat scans were needed, unlike conventional methods.
- Maternal effective dose was lower with CT, even when accounting for retakes in conventional radiography.

## Abstract

Conventional radiographic pelvimetry remains in clinical use to assess pelvic dimensions prior to delivery; however, it often requires multiple projections and may be associated with relatively high radiation doses. As part of a planned ten-year equipment renewal cycle, we evaluated low-dose CT as an alternative approach. Using phantom measurements and patient dose data, we found that low-dose CT pelvimetry reduced pelvic and estimated fetal radiation dose by approximately 40–75% compared with conventional radiography, particularly when accounting for image retakes. Image quality was diagnostically sufficient in all CT examinations, and no repeat scans were required. These findings support the implementation of optimized low-dose CT as a safer, more reproducible, and dose-efficient method for pelvimetric assessment.

Purpose: The present study aimed to assess the radiation dose associated with low-dose (LD) CT pelvimetry compared with conventional radiography and to evaluate the adequacy of the resulting image quality. Methods: The absorbed dose was measured using thermoluminescent dosimeters positioned in an anthropomorphic female phantom, including uterine locations, to estimate the fetal dose. Conventional radiographic pelvimetry and LD-CT pelvimetry were performed using clinically implemented protocols. Effective dose was calculated using Monte Carlo–based modeling applying acquisition parameters and retrospective patient dose registry data. Image quality of LD-CT pelvimetry was independently evaluated in 14 consecutive clinical cases using a four-point ordinal scale. Results: LD-CT pelvimetry reduced the mean absorbed pelvic dose by approximately 50% compared with conventional pelvimetry (0.18 vs. 0.39 mGy) and decreased estimated fetal dose by 40% (0.21 vs. 0.37 mGy). These estimates were based on standardized single acquisitions and did not incorporate additional radiation from retakes commonly observed in conventional practice. CT demonstrated substantially more homogeneous dose distribution, whereas conventional pelvimetry exhibited marked heterogeneity with peak values up to 2.3 mGy. The maternal effective dose was lower for LD-CT (0.16 mSv) than for conventional pelvimetry (0.36 mSv); inclusion of retakes increased the conventional effective dose to 0.71 mSv. All CT examinations were diagnostically adequate, and no recalls were required. Conclusions: Optimized low-dose CT pelvimetry significantly reduces radiation dose compared with conventional radiographic pelvimetry while maintaining reliable diagnostic image quality. These results support the clinical adoption of CT-based pelvimetry as a dose-efficient and reproducible alternative to conventional techniques.