AUA 2024: Investigating Optimal Settings and Thermal Injury Risk of the Thulium Fiber Laser in an Anatomical Kidney Model

( At the AUA 2024 in San Antonio, Dr. Ezra Margolin presented an engaging study that sought to optimize the utilization of the Thulium Fiber Laser (TFL) in stone treatment. Noting the lack of consensus on how to optimize TFL’s clinical application, a comprehensive evaluation to determine the ideal settings for maximum efficacy while minimizing the risk of thermal injury during stone dusting was performed.

Dr. Margolin detailed the utilization of an anatomic hydrogel kidney model derived from human CT imaging, in which stone treatment scenarios were simulated. Cylindrical soft Bego stones, measuring 6 x 6 mm, were strategically positioned in the upper pole calyx of the model. TFL lithotripsy was then performed using a 200 µm fiber inserted through a flexible ureteroscope, with continuous flow irrigation. Various parameters, including pulse energy (Ep), frequency (F), and power settings (W), were systematically adjusted to assess their impact on stone ablation speed and the risk of thermal injury. Temperature changes were monitored using six thermocouples placed near the tissue boundary, while the cumulative equivalent minutes at 43°C (CEM43°C) were calculated to evaluate the risk of tissue injury.
A wide range of TFL settings ranging from 10W to 30W were tested.

Of note, within each power level, as pulse energy increased, and frequency decreased an improvement in efficiency was observed. Dr. Margolin highlighted the contrast from Holmium laser settings which favor low energy and high frequency.
treatment efficiencythermal dose
High-power settings demonstrated the fastest ablation speed, particularly when combined with increased pulse energy. However, it was noted that high-power settings, particularly at 20 W and 30 W, posed a considerable risk of ureteral thermal injury. Conversely, lower pulse energy combined with high frequency resulted in faster temperature increases, potentially reaching levels indicative of thermal tissue injury more rapidly. 10W was considered to give a safe thermal dose and 20W edged close the safety threshold. At 30W high temperature increases that pose significant risk for thermal injury were observed.

The study concludes that optimal efficacy in stone dusting using TFL is achieved with high pulse energy and low-frequency settings, which minimize the risk of passing a safe dosage of thermal energy. However, caution is advised with high-power settings due to the associated risk of thermal injury. The findings underscore the importance of further research to fully understand the implications of different parameter combinations, especially concerning the size of dust particles generated during ablation across various urinary stone types.

At the conclusion of the presentation Dr. Michael Grosso, one of the sessions moderators, emphasized how Dr. Olivier Traxer cited this study in emphasizing that 20W should not be exceeded when operating with TFLs. In agreeance, Dr. Margolin elucidated, “temperature changes are going to be very strongly correlated with your irrigation…with less irrigation, which many of us use in our practice, I’d argue that 20W may be a little bit too high”. Dr. Zachary Tano of UCI Urology posed a follow-up question concerning the model used, specifically whether the heat sync (perfusion) was accounted for during testing. Dr. Margolin concluded that “this is a nonperfused model…we are currently working on a pig model that will hopefully account for that”.

It was certainly an interesting study and presentation by Dr. Margolin that increases anticipation for further in-vivo models to simulate clinical applications more closely.

Presented by: Ezra J. Margolin, MD, Clinical Associate, Department of Urology, Duke University, Durham, North Carolina

Written By: Mark Sarwat Hana, Assistant Research Specialist, Department of Urology, University of California Irvine, at the 2024 American Urological Association (AUA) Annual Meeting, May 3 - 6, 2024, San Antonio, Texas