Effect of CT Attenuation–Stratified Stone Volume on Treatment Outcomes of Shock Wave Lithotripsy for Ureteral Stones

Objectives: Recent advances in three-dimensional (3D) imaging enable precise evaluation of stone characteristics. We investigated predictors of shock wave lithotripsy (SWL) outcomes using CT attenuation–stratified stone volume. Methods: We retrospectively analyzed 313 patients who underwent SWL for ureteral stones between August 2020 and January 2025. Stone-related parameters were measured using 3D imaging software (SYNAPSE VINCENT®), stratifying each stone into seven CT attenuation categories (<1000 HU; 1000–1500 HU in 100-HU increments; ≥1500 HU). A derivation cohort of 259 patients treated with Piezolith® (August 2020–July 2023) determined optimal cutoff values, which were validated in 54 patients treated with Compact Sigma® (August 2023–January 2025). The primary endpoint was conversion to ureteroscopy (URS). Results : Overall, 274 patients (87.5%) achieved SWL success, while 39 (12.5%) required URS. In the validation cohort, predictors of conversion included maximum stone length ≥8.7 mm (OR 7.8, P = 0.02), maximum CT value ≥1487 HU (OR 5.3, P = 0.07), mean CT value ≥535 HU (OR 13.2, P = 0.008), total stone volume ≥152 mm³ (OR 13.2, P = 0.008), and volumes of stone components with CT attenuation ≥1000-1500 HU. Among these, the volume of components ≥1200 HU (21.5 mm³) demonstrated the highest predictive performance (OR 17.7, P = 0.002). Conclusions: CT attenuation–stratified stone volume, particularly components ≥1200 HU, is a strong predictor of SWL failure requiring conversion to URS. Incorporating attenuation-based volumetric analysis into pre-treatment evaluation may improve patient selection and optimize treatment strategy for ureteral stones.