Optimal thulium fiber laser parameters for non-impacted stone lithotripsy: an in-vitro and ex-vivo evaluation.

Optimal parameter settings for thulium fiber laser (TFL) lithotripsy remain controversial, particularly regarding the balance between ablation efficiency and stone retropulsion in non-impacted stones. To address this, we evaluated TFL performance across a wide range of energy–frequency combinations (10–30 W) using an in-vitro BegoStone model to quantify mass loss, retropulsion distance, and fragment-size distribution. Findings were subsequently validated under clinically relevant conditions by fragmenting human struvite stones in an ex-vivo porcine kidney model at 30 W, assessing ablation efficiency, fiber repositioning time, and thermal safety under varying irrigation rates. In-vitro results indicated that pulse energies of 0.3–0.5 J combined with repetition rates of 20–100 Hz consistently produced the highest mass loss and lowest retropulsion, with > 90% of fragments measuring < 250 μm. Conversely, energies > 1 J or frequencies > 100 Hz caused marked increases in retropulsion and reduced efficiency. Ex-vivo validation confirmed that the 0.5 J × 60 Hz setting yielded the greatest ablation efficiency and significantly shortened fiber repositioning time. Furthermore, thermal monitoring revealed that at high-power settings (30 W), irrigation rates of ≥ 30 mL/min were required to maintain intra-renal temperatures below the safety threshold (37.1 °C), whereas low flow (10 mL/min) carried a high risk of thermal injury. In conclusion, TFL lithotripsy performs optimally at 0.3–0.5 J and 20–100 Hz for non-impacted stones, balancing energy deposition with laser-induced hydrodynamic forces. Additionally, adequate irrigation is critical during high-power lithotripsy to ensure thermal safety.