Abstract
OBJECTIVES: Although the thulium fiber laser (TFL, 1940 nm) efficiently fragments stones, concerns have been raised regarding heat production. Recently, a TFL with a modified duty cycle (MDC) was designed to reduce heat generation. The purpose of this study was to compare heat generation between the MDC and conventional TFL. METHODS: Ten millimeter BegoStone phantoms were placed in the proximal ureter of a kidney and ureter model. The model was submerged in a 35°C saline bath, with continuous saline irrigation (22°C) maintained at 15 mL/min through a ureteroscope. Temperature was measured using a needle thermocouple. Five trials of 60 s continuous laser activation were performed for each power setting: 3 W (0.3 J/10 Hz), 10 W (1 J/10 Hz), 20 W (1 J/20 Hz) and 30 W (0.6 J/50 Hz). Thermal dose was calculated as cumulative equivalent minutes at 43°C (CEM₄₃; injury threshold> 20). Kruskal-Wallis and Mann-Whitney U tests were used for statistical analysis with p < 0.05 being significant. RESULTS: Both lasers produced maximum temperatures (T(max)) of 27°C at 3 W. The MDC TFL generated a significantly lower Tmax than the conventional TFL at 10 W (36.9°C vs 42.1°C, p < 0.001), 20 W (38.1°C vs 44.6°C, p < 0.001), and 30 W (52.5°C vs 63.6°C, p < 0.05). CEM₄₃ for the MDC and conventional TFL at 20 W were (0.00 vs 0.90, respectively), and at 30 W (425 vs 275,919, respectively). CONCLUSIONS: The MDC TFL generated lower temperatures at 10, 20, and 30 W. Future studies are necessary to evaluate stone fragmentation efficiency of the MDC TFL.