Laser Fiber Displacement Velocity during Tm-Fiber and Ho:YAG Laser Lithotripsy: Introducing the Concept of Optimal Displacement Velocity

Abstract

Background: Endocorporeal laser lithotripsy (EL) during flexible ureteroscopy (URS-f) often uses “dusting” settings with “painting” technique. The displacement velocity of the laser fiber (LF) at the stone surface remains unknown and could improve EL’s ablation rates. This in vitro study aimed to define the optimal displacement velocity (ODV) for both holmium:yttrium-aluminium-garnet (Ho:YAG) and thulium fiber laser (Tm-Fiber). Methods: A 50W-TFL (IRE Polus®, Russia) and a 30W-MH1-Ho:YAG laser (Rocamed®), were used with 272µm-Core-Diameter LF (Sureflex, Boston Scientific©), comparing three TFL modes, “fine dusting” (FD:0.05–0.15 J/100–600 Hz); “dusting” (D:0.5 J/30–60 Hz); “fragmentation” (Fr:1 J/15–30 Hz) and two Ho:YAG modes (D:0.5 J/20 Hz, Fr:1 J/15 Hz). An experimental setup consisting of immerged cubes of calcium oxalate monohydrate (COM) stone phantoms (Begostone Plus, Begoã) was used with a 2 seconds’ laser operation time. LF were in contact with the stones, static or with a displacement of 5, 10 or 20 mm. Experiments were repeated four times. Stones were dried and µ-scanned. Ablation volumes (mm3) were measured by 3D-segmentation. Results: ODV was higher in dusting compared to fragmentation mode during Ho:YAG lithotripsy (10 mm/sec vs. 5 mm/sec, respectively). With Tm-Fiber, dusting and fragmentation OVDs were similar (5 mm/sec). Tm-Fiber ODV was lower than Ho:YAGs in dusting settings (5 mm/s vs. 10 mm/sec, respectively). Without LF displacement, ablation volumes were at least two-fold higher with Tm-Fiber compared to Ho:YAG. Despite the LF-DV, we report a 1.5 to 5-fold higher ablation volume with Tm-Fiber compared to Ho:YAG. Conclusions: In dusting mode, the ODVTm-Fiber is lower compared to ODVHo:YAG, translating to a potential easier Tm-Fiber utilization for “painting” dusting technique. The ODV determinants remain unknown. Dynamic ablation volumes are higher to static ones, regardless of the laser source, settings or LF displacement velocity.

The Optimal Combination of Scanning Speed and Fiber-to-Stone Distance for Effective and Efficient Dusting during Holmium: YAG Laser Lithotripsy

“…Under similar settings (0.5 J, 20 Hz) using another laser lithotripter with different pulse profiles, the maximum dusting efficiency could be achieved at even higher v fiber of 10 mm/s (23). However, it should be noted that slow v fiber is much easier to manipulate during clinical LL and preferable over fast scanning speeds to avoid unintentional ureteral wall injury (23).…”

“…Moreover, careful adjustment of the fiber tip to stone surface distance (or SD) has been recommended for clinical LL (5), and its influence on treatment outcome demonstrated recently in laboratory studies (19,28). Furthermore, scanning the fiber tip over the stone surface may avoid saturation in stone damage when laser pulses are delivered to a fixed spot (23,44). However, the optimal v fiber and SD have not been determined, nor has the associated mechanism of action been elucidated.…”

“…This observation is consistent with previous studies, in which a faster scanning speed (e.g., 3 mm/s vs. 1 mm/s) was found to produce higher dusting efficiency regardless of PRF in contact mode (13). Under similar settings (0.5 J, 20 Hz) using another laser lithotripter with different pulse profiles, the maximum dusting efficiency could be achieved at even higher v fiber of 10 mm/s (23). However, it should be noted that slow v fiber is much easier to manipulate during clinical LL and preferable over fast scanning speeds to avoid unintentional ureteral wall injury (23).…”

“…At E p = 0.5 J and PRF = 20 Hz, Alhoukhi and colleagues compared two clinically relevant fiber scanning speeds and found that the mass loss was much greater at 3 mm/s than at 1 mm/s (13). Using similar settings, Panthier et al demonstrated that the maximum stone damage could be produced at v fiber = 10 mm/s or 2.5 mm/s, compared to lower scanning speeds (23). Both studies used BegoStone phantoms, yet the mechanism that led to maximum efficiency in stone dusting was not investigated.…”

The Effects of Scanning Speed and Standoff Distance of the Fiber on Dusting Efficiency during Short Pulse Holmium: YAG Laser Lithotripsy

“…At E p = 0.5 J and F = 20 Hz (with a 230 mm core diameter), Alhoukhi and colleagues compared two clinically relevant fiber scanning speeds and found that the mass loss was much greater at 3 mm/s than at 1 mm/s [ 13 ]. Using similar settings (with a 272 mm core diameter), Panthier et al demonstrated that the maximum stone damage could be produced at v fiber = 10 mm/s or 2.5 mm/s, compared to lower scanning speeds [ 23 ]. Both studies used BegoStone phantoms, yet the mechanism that led to maximum efficiency in stone dusting was not investigated.…”