Thulium versus holmium for in situ lower pole laser lithotripsy.

During in situ lower pole laser lithotripsy, the dependent location may result in increased challenge fragmenting stones and a risk for stone regrowth if residual fragments remain. The purpose of this study was to compare the thulium fiber laser (TFL) with the holmium laser (HL) for in situ lower pole lithotripsy.In a 3D printed kidney benchtop model, sixty 1 cm BegoStones were placed in the lower pole and fragmented in situ until fragments passed through a 2 x 2 mm mesh. Laser lithotripsy was performed using twelve energy, frequency and fiber size combinations and residual fragments were compared. In addition, laser fiber diameters and subsequent ureteroscope deflections and flow rates were compared between fibers.The TFL resulted in decreased residual fragments compared to the HL (11% vs. 17%, p < 0.001) and the three settings with least residual fragments were all TFL. Compared to the 150 µm TFL (265° deflection), there was a loss of 9° and 34° in the 200 µm TFL and 272 µm HL fibers, respectively. The measured fiber sizes were greater than manufacturer specified fiber size in every instance. Irrigation rates inversely correlated with fiber size.The TFL resulted in 35% less residual stone fragments, up to 34° additional deflection, and an increased irrigation rate when compared to the HL. Optimal fragmentation settings are identified to further improve lower pole lithotripsy. The combination of reduced residual fragments, improved deflection, and better flow rates make the TFL advantageous for in situ lower pole lithotripsy.