When long pulse is not enough: inferior dusting efficiency of pulsed thulium:YAG compared with Ho:YAG and thulium fiber laser in a standardized in vitro renal model.

Pulsed thulium: YAG (p-Tm: YAG) and thulium fiber laser (TFL) differ in pulse architecture despite similar wavelengths. We asked whether long-pulse p-Tm: YAG achieves ablation efficiency and thermal behaviour comparable to holmium: YAG (Ho: YAG) and TFL under standardized low-power dusting settings. Fifty-four BegoStone phantoms were treated in an in vitro renal collecting system model, 18 per platform, at 0.8 J and 25 Hz through a 7.5 Fr single-use flexible ureteroscope with gravity irrigation and no access sheath. Pulse duration was not standardized: Ho: YAG and p-Tm: YAG were long-pulse, TFL short-pulse. Ablated dry mass, laser-on time, delivered energy, temperature every 10 s and thermal dose (CEM43, per run) were recorded. p-Tm: YAG ablated 0.099 g versus 0.138 g (Ho: YAG) and 0.140 g (TFL) (p = 0.005), a 29% reduction, despite delivered energy indistinguishable from Ho: YAG (5.61 versus 5.62 kJ; p = 1.000). Energy efficiency was 0.0176 versus 0.0248 and 0.0242 g·kJ⁻¹ (p = 0.007). Both thulium platforms heated more than Ho: YAG (ΔT 18.8 and 18.9 versus 12.8 °C; p = 0.001) but did not differ from each other. Temperature exceeded 43 °C in 17 of 36 thulium runs (peak 51.7 °C); mean per-run CEM43 was 24.4 and 14.5 min. For equivalent delivered energy, long-pulse p-Tm: YAG was associated with lower ablation efficiency than Ho: YAG or short-pulse TFL. Because pulse duration was confounded with platform, these findings implicate pulse architecture rather than intrinsic inferiority. Frequent excursions above 43 °C with both thulium platforms warrant attention.