This study offers the first head-to-head comparison of intrapelvic temperature profiles generated by pulsed thulium: YAG (Tm: YAG), thulium fiber laser (TFL), and holmium: YAG with pulse modulation (MOSES 2.0) under standardized dusting parameters in an ex vivo porcine kidney model. The principal finding was that TFL produced significantly higher intrapelvic temperature elevations than both Tm: YAG and MOSES 2.0, despite using less total energy. Nevertheless, under conditions of active irrigation and unobstructed outflow using a 10/12 Fr ureteral access sheath above the ureteropelvic junction at 150 mmHg, none of the systems exceeded the commonly cited 43 °C thermal safety threshold [2,3,4] during 10 min of near-continuous activation. These findings suggest that, in settings with sufficient irrigation and drainage, all three laser platforms are capable of operating within a thermally safe range.

The greater temperature elevations observed with TFL are consistent with its emission profile and the higher water absorption coefficient at its 1940 nm wavelength [5]. Although these properties enhance vaporization efficiency, they also confine thermal deposition to a smaller intraluminal volume. By contrast, MOSES 2.0 produced the lowest temperature rise, aligning with its dual-pulse modulation intended to optimize cavitational energy transfer while limiting residual heat with a lower water absorption coefficient (2140 nm) [4]. Pulsed Tm: YAG demonstrated intermediate thermal behavior, reflecting its middle fluid absorption wavelength (2013 nm) between the TFL and holmium systems. Energy-normalized comparisons further highlight these mechanistic distinctions: on a per-kilojoule basis, TFL generated more than twice the temperature increase observed with either MOSES 2.0 or Tm: YAG. Thermal dose metrics such as cumulative equivalent minutes at 43 °C (CEM43) provide additional biological context beyond peak temperature alone. In this study, no specimen exceeded 43 °C during lithotripsy, and under these subthreshold conditions any calculated CEM43 would be extremely low and well below injury-associated thresholds. Given the use of room-temperature irrigation, which likely provided convective cooling and conservative temperature estimates, analysis focused on peak temperature change and energy-normalized heat generation, consistent with the format of prior endourologic thermal studies.

Several prior experimental studies have reported minimal or no clinically meaningful differences in intrarenal heat generation among Ho: YAG and thulium-based laser systems, and these findings should be interpreted in the context of the experimental conditions under which they were obtained. For example, Okhunov et al. demonstrated in an in vivo porcine model that TFL did not result in sustained suprathreshold intrarenal temperatures; in that study, a 12/14 Fr ureteral access sheath was used, and physiologic renal perfusion in the live animal likely provided additional convective cooling [11]. Similarly, Jiang et al. reported comparable intrarenal temperature profiles between TFL and Ho: YAG in an in vivo porcine model, with no temperatures exceeding 44 °C, again using a larger 12/14 Fr access sheath and benefiting from blood-flow–mediated heat dissipation [12]. Accordingly, the present findings should be viewed as complementary to the existing literature, reflecting relative thermal behavior under the specific experimental conditions and setup employed (10/12 Fr ureteral access sheath advanced to the ureteropelvic junction in an ex vivo environment).

The experimental model incorporated a 10/12 Fr ureteral access sheath advanced into the renal pelvis past the ureteropelvic junction and continuous pressurized irrigation (150 mmHg), both of which promote robust inflow and outflow. Accordingly, these findings may not fully translate to scenarios lacking an access sheath, to cases in which the sheath terminates below the ureteropelvic junction, or to situations with reduced irrigation. Localized environments with restricted egress—such as a calyx with a tight infundibulum. a narrow ureter, or sheath below the ureteropelvic junction—may exhibit substantially different thermal behavior. This concern is supported by an in vivo porcine study demonstrating that TFL activation without a ureteral access sheath can lead to intrarenal temperatures exceeding 44 °C under similar dusting and fragmentation settings [11]. Additionally, even the holmium laser without a ureteral access sheath has been demonstrated to generate high intrarenal temperatures (43.1 °C) in an ex vivo porcine kidney model. Thus, while all systems operated within safe thermal limits under the conditions tested, the results should be interpreted within the context of the model with ample fluid exchange (150 mmHg irrigation pressure with a 10/12 F UAS above the ureteropelvic junction). However, all this considered, the data are likely generalizable to settings with larger-caliber access sheaths (14–16 Fr) or a 10/12 Fr sheath used with higher irrigation pressures, where flow dynamics would be expected to be equal or more favorable than in the present study [12].

This study has several limitations. It was conducted ex vivo, without physiologic perfusion or urine production to provide additional convective cooling. Temperature measurements were limited to the renal pelvis and therefore may not reflect microenvironmental temperatures at the laser tip or within anatomically constrained spaces. Furthermore, heat conducted directly into the stone was not assessed; consequently, while bulk fluid temperatures remained within safe limits, the peak temperature achieved within the stone itself cannot be inferred. Despite these constraints, the use of standardized methodology, similar laser parameters, and a setup that closely approximates practical operating conditions permits a valid ex vivo comparison of relative thermal behavior among the evaluated systems for the first time in literature.

Furthermore, laser parameters were selected using manufacturer-recommended dusting settings; however, the MOSES 2.0 system has a minimum allowable pulse frequency of 60 Hz at 0.3 J, which precluded exact matching to the 50 Hz settings used for the thulium-based systems at the same pulse energy. As a result, a small difference in nominal power (15–18 W) was unavoidable. To mitigate this limitation, temperature change was additionally normalized to the exact total energy delivered, yielding consistent relative differences across platforms. Nonetheless, manufacturer-recommended settings are not necessarily optimized for thermal efficiency or safety, and future studies using fully matched power and duty-cycle conditions may further refine comparative thermal assessments. Finally, laser activation duration and firing pattern represent important determinants of intrarenal heat generation. In this study, near-continuous laser activation over a 10-minute interval was used to approximate typical clinical lithotripsy behavior rather than a fixed-duty-cycle paradigm; however, this approach may introduce inter-operator variability, particularly in a bench model involving multiple surgeons. Accordingly, this represents a limitation of the study, and future investigations incorporating both strictly controlled activation protocols and clinically simulated lithotripsy conditions may further refine comparative thermal assessments.