Introduction

To date Holmium (Ho) laser is one of the most popular and effective tools_x000D_ for lithotripsy. It emits very short pulses (0.1 – 1 ms) with high peak power (0.5-10 kW) that allows to efficiently fragment any type of urinary stones. Series of articles show Ho laser wavelength of 2.1 µm is significantly off the peak of water absorption, and so can negatively affect efficiency of stone fragmentation._x000D_ They also stressed that the thulium (Tm) fiber laser with diode laser pumping can improve stone fragmentation, because emission of Tm laser with wavelength 1.94 µm is 4.5 times stronger absorbed by water than that of Ho laser._x000D_ _x000D_ There is a lot of data on feasibility and efficacy of Tm laser application for stone fragmentation in vitro. _x000D_ _x000D_ Nevertheless, Thulium laser lithotripsy hasn’t been widely utilized in the clinical settings._x000D_ _x000D_ A prototype Tm fiber laser with a peak power up to 500 W were developed by NTO «IRE – Polus»

Methods

We have evaluated in vitro performance of a prototype Tm fiber laser with a peak power up to 500 W as a potentially alternative for modern Ho laser system._x000D_ The in vitro experimental setup for measuring the stone fragmentation rate (ablation rate) included a specially designed cuvette with several levels of meshes allowing for precise quantification of size distribution of stone fragments (for the modes of fragmentation and dusting). Post – surgery human stones and BegoStone phantoms were used. The laser parameters (pulse energy and average power) were identical._x000D_ Also retropulsion effect caused by a single pulse has been evaluated. Lateral shift of a stone after a single pulse of laser energy was measured._x000D_

Results

¥ Proposed experimental technique offers relatively simple and reliable method of comparing performance of laser lithotripters under controlled ex vivo conditions_x000D_ ¥ The Tm system, at identical laser parameters, produced about 2.3 and 1.3 times greater average ablation rate than the Ho system does in dusting and fragmentation modes, respectively_x000D_ ¥ The ratio of ablation rates on BegoStone phantoms correlated well with human stone data and varied between 1.6 and 2.3_x000D_ ¥ The effect of retropulsion of the Tm laser (at 500 W) was 75%, 60%, and 29% of that of the Ho laser for equal pulse energies of 1, 2, and 3 J, respectively. The retropulsion onset threshold was significantly higher for Tm laser_x000D_

Conclusions

Supported by this experimental data we assessed the clinical effectiveness of Tm fiber Urolase system with peak power of 120 W for lithotripsy. Several bladder stones with the average size about 1.9 cm were successfully destroyed. _x000D_ Further investigation in to the clinical applicability of Thulium lithotripsy is required._x000D_

Funding

none