Holmium:YAG vs thulium fiber laser dusting of calcium oxalate monohydrate stones

Abstract

Recent advances in Holmium and Thulium fiber lasers (TFL) enable operation at similar parameters for comparison. A ‘dusting’ lithotripsy mode with low energy per pulse (0.2-0.4 J) and high pulse rates (50-80 Hz), is preferred to produce smaller residual stone fragments for natural passage through the urinary tract. Holmium and TFL were compared for dusting using three groups, G1: 0.2 J/50 Hz/10 W; G2: 0.2 J/80 Hz/16 W; and G3: 0.4 J/80 Hz/32 W. A setup with 1 x 1 cm cuvette and 1.0 mm sieve was used with total laser operation time limited to ≤ 5 min. Calcium oxalate monohydrate (COM) stones with average initial stone mass of 216-297 mg between groups were used. Holmium ablation rates were lower than for TFL at all settings (G1: 0.3 ± 0.2 vs. 0.8 ± 0.2; G2: 0.6 ± 0.1 vs. 1.0 ± 0.4; G3: 0.7 ± 0.2 vs. 1.3 ± 0.9 mg/s). TFL also produced a greater percentage by mass of stone dust (< 0.5 mm) than Holmium. For all three settings, 1/15 (7%) stones treated with Holmium were fragmented in ≤ 5 min vs. 9/15 (60%) stones treated with TFL. These preliminary studies demonstrate that TFL is a viable laser for stone dusting, producing higher stone ablation rates and smaller stone fragments than Holmium laser.