Assessment of the Optimal Settings of TFL for Laser Lithotripsy and Associated Thermal Injury Risk

ABSTRACT Urinary stone disease (USD) is on the rise and represents the second most costly urologic condition in the United States, with a healthcare expenditure over $2 billion per year. Most notably, the landscape of ureteroscopy (URS) via laser lithotripsy (LL) - the leading treatment option for USD is experiencing a rapid and dramatic technological evolution, driven primarily by the launch of the Thulium Fiber Laser (TFL) in 2020 and its growing clinical applications, but also heightened by the introduction of the Dornier Thulio laser in 2022. However, despite the great clinical enthusiasm about these new laser technologies, there is no consensus among urologists regarding the optimal settings for TFL in LL. In addition, because the TFL is much more strongly absorbed in water than the Holmium (Ho):YAG laser, the temperature can rise rapidly, especially when treating impacted stones in the ureter. Therefore, in this new era of LL, there is a pressing need to better understand the mechanism of action for TFL, and to distinguish its similarities and differences from the Ho:YAG lasers in terms of stone ablation capability and tissue injury risk. To address these fundamental challenges/unmet clinical needs, we propose three specific aims: 1) To determine the optimal settings of TFL - in vitro studies to explore a wide range of parameters; 2) To elucidate the mechanisms of action by TFL via experimental and numerical investigations; and 3) To define the best clinical LL strategy using TFL in artificial kidney/ureter phantoms and swine model. Altogether, we strive to unravel the intricate laser-fluid-bubble-stone interactions and their interconnections that cannot be easily observed or appreciated during clinical laser lithotripsy. Through such a grand effort, we hope to develop the best treatment strategy for achieving the most desirable outcomes (i.e., the highest stone ablation efficiency, lowest heat-induced injury risk, and shortest procedure time) for urinary stone treatment using the burgeoning TFL technology. Considering the growing epidemic of USD, coupled with the rapid advance in LL technology and techniques, the proposed investigation is timely and well justified. The outcome of the project is anticipated to impact the long-term surgical management of USD and advance of future LL technology.