High power holmium:YAG versus thulium fiber laser treatment of kidney stones in dusting mode: ablation rate and fragment size studies

Objectives The experimental Thulium fiber laser (TFL) is currently being studied as a potential alternative to the gold standard Holmium:YAG laser for lithotripsy. Recent advances in both Holmium and TFL technology allow operation at similar laser parameters for direct comparison. The use of a "dusting" mode with low pulse energy (0.2-0.4 J) and high pulse rate (50-80 Hz) settings, is gaining popularity in lithotripsy due to the desire to produce smaller residual stone fragments during ablation, capable of being spontaneously passed through the urinary tract. Methods In this study, Holmium and TFL were directly compared for 'dusting' using three laser 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. Holmium laser pulse durations ranged from 200 to 350 mu s, while TFL pulse durations ranged from 500 to 1,000 mu s, due to technical limitations for both laser systems. An experimental setup consisting of 1 x 1 cm cuvette with 1 mm sieve was used with continuous laser operation time limited to <= 5 minutes. Calcium oxalate monohydrate stone samples with a sample size of n = 5 were used for each group, with average initial stone mass ranging from 216 to 297 mg among groups. Results Holmium laser ablation rates were lower than for TFL at all three 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). The TFL also produced a greater percentage by mass of stone dust (fragments <0.5 mm) than Holmium laser. For all three settings combined, one out of 15 (7%) stones treated with Holmium laser were completely fragmented in <= 5 minutes compared to nine out of 15 (60%) stones treated with TFL. Conclusions These preliminary studies demonstrate that the TFL is a promising alternative laser for lithotripsy when operated in dusting mode, producing higher stone ablation rates and smaller stone fragments than the Holmium laser. Clinical studies are warranted. Lasers Surg. Med. 51:522-530, 2019. (c) 2019 Wiley Periodicals, Inc.