Geometric agreement in pedicle morphometrics and screw planning between tin-filtered ultra-low-dose CT and standard-dose CT: an exploratory cadaveric study

Patient-specific guides improve pedicle screw placement in pediatric deformity surgery, but the preoperative CT entails radiation. Tin-filtered ultra-low-dose CT reduces dose, yet its effect on vertebral segmentation and pedicle screw planning remains unknown. This study therefore assesses geometric agreement between tin-filtered ultra-low-dose CT and standard-dose CT. Five ultra-low-dose and five standard-dose CT scans of one human cadaver were obtained. Vertebrae T2, L2 and S1 were segmented to quantify within- and between-protocol variability of pedicle morphometrics. For planning analysis, screws (T2-S1) were planned on the first standard-dose scan and transferred to the ultra-low-dose segmentations (fixed screw positions). Accuracy was evaluated using the Gertzbein-Robbins scale and screw-to-cortex distances. Pedicle morphometrics differed by ≤ 0.5 mm between protocols, with higher variability on ultra-low-dose CT (CV < 5% for both protocols). After transfer of planned screws from standard-dose to ultra-low-dose segmentations, all remained Gertzbein-Robbins grade A. Ultra-low-dose CT yielded larger screw-to-cortex clearances, with mean absolute differences of 0.14 mm to the medial cortex, 0.21 mm to the superior cortex, and 0.71 mm from screw tip to anterior cortex. Tin-filtered ultra-low-dose CT reduced radiation by > 75%, while preserving sub-millimeter agreement in pedicle morphometrics and screw-to-cortex clearances, suggesting minimal impact on the pedicle screw planning.