Optimizing Fragmentation while Minimizing Thermal Injury Risk with the Thulium Fiber Laser in Ureteral Stone Lithotripsy: An In Vitro Study.

Objective: To optimize thulium fiber laser (TFL) settings for effective stone fragmentation although minimizing thermal injury in confined ureteral spaces using a three-dimensional ureter model. Materials and Methods: A hydrogel-based ureter model was maintained at 37.2 ± 0.5°C, with a cylindrical BegoStone (10 × 10 mm, 1.00 ± 0.07 gm) occluding the ureter. Ureteroscopy was performed using a 150 µm TFL fiber for 3 minutes with room temperature irrigation and differing rates (0, 20, 40 mL/min) and power settings (6.4 to 20 W). Maximum sustained temperature (MST) and cumulative thermal dose (cumulative equivalent minutes at 43°C) were assessed against a 120-minute safety threshold. We also evaluated the effects of ureter volume and irrigation temperature. Stone mass treated was calculated by subtracting the mass of residual fragments >3 mm from the initial mass. Results: At 6.4 and 10 W, MSTs were below body temperature, and thermal doses were under 1 minute, indicating minimal thermal risk. At 20 W with 20 mL/min irrigation, MST exceeded 43°C within seconds, and thermal doses surpassed 120 minutes. Treatment efficiency was highest at 20 W (1.58 mg/s), followed by 10 W (1.15 mg/s) and 6.4 W (0.78 mg/s). Among 10 W settings, 1.0 J/10 Hz was more efficient than 2.0 J/5 Hz and 3.0 J/3 Hz. Safe settings produced 95.5% fine dust, whereas high-energy pulses 2-3 J produced significantly more fragments (1-3 mm) compared with settings with pulse energy 0.5-1.0 J. Increasing irrigation to 40 mL/min or using 15°C irrigation effectively reduced MST and improved efficiency, particularly at 20 W. Conclusion: Our study demonstrates the risk of thermal injury with 20 W TFL treatment. Conversely, 10 W settings at 2.0 J/5 Hz are safe and effective for fragmentation. Future research will focus on validating these optimal settings for human stone treatment.

Duke Scholars

Author Arpit Mishra  

Author Jodi Antonelli Urology

Author Robert Medairos Urology

Author Michael Eric Lipkin Urology

Author Glenn Michael Preminger Urology

Author Pei Zhong Thomas Lord Department of Mechanical Engineering and Materia ...