Assessment of Holmium:YAG, Pulsed-Thulium:YAG and Thulium Fiber Lasers for Urinary Stone Ablation. In Vitro Study

Abstract

Objective: To evaluate the ablation speed (AS), laser efficiency and direct thermal lesions during urinary stone lithotripsy with the current available laser technologies: Holmium:YAG (Ho:YAG), pulsed-Thulium:YAG (p-Tm:YAG) and thulium fiber laser (TFL) in vitro using different laser settings. Materials and Methods: Ho:YAG, p-Tm:YAG, and TFL laser system were used in an in vitro ureteral model with a volume of 125 mm³ Begostone. The following parameters were tested across all laser devices: 0.6J/10 Hz (6 W), 0.6 J/20 Hz (12 W), 1.5 J/10 Hz (15 W), and 1.5 J/20 Hz (30 W), employing short pulse width for all lasers and long pulse width for Ho:YAG and p-Tm:YAG. Ten participants conducted the experimental setup during 3-minutes laser on time, combining the laser technology, settings, and pulse widths, with a total of 20 different combinations. The efficiency, AS and ureteral damage resulting from each intervention were analyzed. Results: p-Tm:YAG and TFL demonstrated significantly higher efficiency compared with Ho:YAG (0.049 ± 0.02 Δgr/KJ and 0.042 ± 0.01 Δgr/KJ vs 0.029 ± 0.01 Δgr/KJ; p < 0.05). In all laser sources, as the power increases, the AS also increases (p < 0.05). Furthermore, only at high-energy settings (1.5 J) higher frequency led to increase AS (p < 0.05). Both, p-Tm:YAG and TFL exhibited higher AS compared to Ho:YAG (0.64 ± 0.33 Δgr/s and 0.62 ± 0.31 Δgr/s vs 0.44 ± 0.22 Δgr/s; p < 0.05). Regarding ureteral injuries, as the power increases, there is a higher chance of ureteral damage (p = 0.031). No differences were observed between laser technologies (p = 0.828). Conclusions: Both, p-Tm:YAG and TFL exhibited superior performances during laser lithotripsy compared with Ho:YAG, as they demonstrated higher efficiency and ablation speed. Thermal damage did not appear to be associated with specific laser equipment, but higher grades of lesions are described by increasing power.

Keywords: Holmium YAG; laser efficiency; laser parameters; laser setting; pulsed-thulium YAG; thermal damage; thulium fiber laser; urinary stones.