Category: New Technology: Stones

MP5-9 - Comparison of high power Holmium:YAG and Thulium fiber lasers for dusting of calcium oxalate monohydrate stones

Fri, Sep 21
10:00 AM - 12:00 PM

Introduction & Objective :

The Thulium fiber laser (TFL) is being studied as an alternative to Holmium:YAG laser for lithotripsy.  TFL advantages include more flexible operating parameters, use of smaller fibers, and higher stone ablation rates.  This laboratory study compares stone ablation rates and fragment sizes between Holmium and TFL for dusting stones using high power settings.


Methods :

Holmium laser (λ = 2120 nm) and TFL (λ = 1940 nm) were compared, using 200-µm optical fibers.  Three laser settings (G1, G2, G3) were chosen, based on pulse energy / pulse rate / power, including 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.  Five calcium oxalate monohydrate stones were used for each setting, and 15 stones for each laser, with average initial stone mass ranging from 216 to 297 mg.  The experimental setup consisted of 1 x 1 cm cuvette with 1 mm sieve and inflow / outflow ports connected to saline pumps.  A separate 0.5 mm sieve collected fragments passing through 1 mm sieve.  Stone ablation rate (mg/s) was calculated by subtracting final stone mass from initial stone mass and dividing by time, with continuous laser operation time limited to ≤ 5 min.  Percentage of stone fragments < 0.5 mm, 0.5 - 1.0 mm, and > 1.0 mm were also compared for each laser and setting.  


Results :

For all three settings, TFL ablation rate was higher than for Holmium laser (G1:  0.8 ± 0.2 vs. 0.3 ± 0.2, p = 0.01; G2:  1.0 ± 0.4 vs. 0.6 ± 0.1, p = 0.04; G3:  1.3 ± 0.9 vs. 0.7 ± 0.2 mg/s. For 32 W (G3), results were not statistically significant, due to strong stone retropulsion effects observed.  For all settings combined, 9 out of 15 (60%) stones treated with TFL were fragmented in ≤ 5 min, while only 1 out of 15 (7%) stones treated with Holmium laser were fragmented in ≤ 5 min.  TFL also produced a greater percentage of smaller stone fragments (< 1 mm) than Holmium laser for each setting, although this was not statistically significant for all groups.  Percentages of stone fragments < 0.5 mm were:  G1:  73 ± 14 vs. 34 ± 16;  G2:  78 ± 12 vs. 71 ± 8;  G3:  86 ± 4 vs. 73 ± 10 %.  Percentages of stone fragments between 0.5 - 1.0 mm were:  G1:  4 ± 4 vs. 2 ± 1;  G2:  11 ± 5 vs. 4 ± 2;  G3:  14 ± 4 vs. 10 ± 7 %.  Percentage of stone fragments > 1.0 mm were:  G1:  23 ± 17 vs. 65 ± 17;  G2:  11 ± 16 vs. 25 ± 9;  G3:  0 vs. 17 ± 14 %. 


Conclusions :

These preliminary studies show that Thulium fiber laser is a promising alternative laser for lithotripsy in dusting mode, resulting in higher ablation rates and smaller stone fragments than Holmium laser.  Future clinical studies to evaluate TFL are warranted.

Viktoriya Andreeva

Engineer
Moscow Engineering Physics Institute
Moscow, Moskva, Russia

Viktoriia Andreeva
Engineer, National Research Nuclear University Moscow Engineering Physical Institute

Luke Hardy

Graduate Student
University of North Carolina at Charlotte
Charlotte, North Carolina

Nathaniel Fried

Professor
University of North Carolina at Charlotte
Charlotte, North Carolina