Thulium versus holmium: Which is safer for the removal of entombed stents?

Introduction: Removal of entombed ureteral stents can be technically challenging, particularly if the stent were to fragment during removal. The purpose of this study was to compare the therapeutic suitability of the thulium fiber laser (TFL) and the holmium laser (HL) in the treatment of entombed stents. Methods: In this benchtop study, first, the time taken for each laser to transect the stent was recorded in 10 experiments/laser. Next, the force required to break the stent following 5 s of laser contact was measured in 15 randomized experiments/laser. Finally, seven experiments of simulated ureteroscopy on entombed stents were performed per laser. Lasers were operated at 0.8 J, 12 Hz with 270 μm fibers, and 6 Fr stents were utilized. Endpoints included time to release the stent, laser energy, and stent damage. Results: The stent transection time was shorter with the TFL compared to the HL (22.02 vs. 61.46 s; P < 0.001). After 5 s, the TFL transected the stent with lesser force compared to the HL (5.34 vs. 15.24 N; P = 0.004). Both required lesser force to break the stent compared to the baseline (33.8 N; P < 0.001). On simulated lithotripsy, the lithotripsy time (12.7 vs. 8.5 min; P = 0.11) and laser energy (4.7 vs. 2.7 kJ; P = 0.09) were similar between the TFL and HL. The mean stent damage score was higher when using the TFL compared to the HL (36.9 vs. 15.7; P = 0.017). Conclusions: The TFL resulted in faster stent transection, reduced breakage force, and greater stent damage. Urologists should be cautious when releasing entombed stents using the TFL as the laser may significantly weaken the stent, increasing the risk of fracture during removal.