Radiation exposure for planning deformity corrections with hexapods: comparison of conventional X-ray, standard CT, and ultra-low-dose CT.

INTRODUCTION: Hexapod systems are among the most accurate devices for correcting complex bone deformities. Postoperative planning is carried out using web-based software solutions based on at least two X-ray images in orthogonal planes. Recent studies have shown that inaccuracies in determining mounting parameters and the spatial relationship between the reference ring and the bone may lead to measurement errors. Computed tomography images potentially offer greater accuracy in this regard, but are associated with increased radiation exposure. The aim of this study was to compare radiation exposure from conventional radiography (X-ray), standard computed tomography (CT), and ultra-low-dose CT (ULD-CT) in the context of planning deformity corrections using a hexapod system and to evaluate suitability and comparability of these imaging modalities for treatment planning. MATERIALS AND METHODS: Between March 1, 2022, and August 31, 2024, 28 patients were treated with a hexapod system for post-traumatic deformities at a Level I trauma center. All patients for whom standardized radiographs (anteroposterior and mediolateral views), conventional CT scans, and ULD-CT scans were available were included in this retrospective analysis. The study population thus comprised n = 18 patients. The effective radiation dose (µSv) was calculated separately for each examination. The values were compared using descriptive statistics and inferential analysis (repeated-measures ANOVA; p < 0.05). RESULTS: The mean effective dose was 1.41 µSv (min 0.66 µSv, max 2.53 µSv, SD ± 0.6 µSv) for conventional X-rays, 4.61 µSv (min 2.97 µSv, max 6.68 µSv, SD ± 1.00 µSv) for ULD-CT, and 150.8 µSv (min 94.85 µSv, max 224.6 µSv, SD ± 35.81 µSv) for standard CT. ULD-CT showed significantly lower radiation exposure than standard CT while offering sufficient image quality for treatment planning. Although the radiation dose of ULD-CT was higher than that of X-rays, but in relation to the measurement precision achieved, there was a clear reduction in dose compared to standard CT. CONCLUSION: ULD-CT provides image quality suitable for treatment planning comparable to standard CT with significantly reduced radiation exposure. Given the significantly improved planning quality and acceptable dose, ULD-CT can be recommended as a favorable balance between precision and radiation protection. In conclusion, ULD-CT represents a valuable imaging option for obtaining the most accurate determination of the distance between two points, particularly when defining mounting parameters.