Soft Tissue Safety Assessment of Pulsed Solid-State Thulium:YAG Versus Holmium:YAG Lasers

OBJECTIVESLaser lithotripsy carries an inevitable risk of collateral tissue injury. This study compared the safety profiles of pulsed Holmium:YAG and Thulium:YAG lasers by examining their effects on soft tissue under laser settings relevant to lithotripsy, using ex vivo porcine kidney models.

METHODSDirect laser impacts were applied to porcine renal parenchyma and pelvis at constant fiber movements and clinical laser settings (0.2-3.5 J, 10-40 Hz, 2-40 W), with high-power extensions for the Thulium:YAG laser up to 80 W/200 Hz. From 560 histological sections, coagulation and cutting depths were measured and clustered.

RESULTSAt equivalent power, the Thulium:YAG laser operated with longer pulses than Holmium:YAG, reducing pulse energy per time (pulse power ≤ 3362 vs. ≤ 7777 W). Holmium:YAG laser produced deeper lacerations up to 9.3 mm in renal parenchyma, compared to 5.0 mm with the Thulium:YAG laser. In renal pelvis, maximal cut depth was 3.6 mm with Holmium:YAG-twice as that observed with the Thulium:YAG. While pulse power was a primary determinant for soft tissue damage, high frequencies (100-200 Hz) did not elevate it. Cluster analysis identified laser-specific damage profiles: Thulium:YAG favored coagulative damage at limited depths, whereas Holmium:YAG induced deep lacerations with limited coagulation and tissue detachment.

CONCLUSIONSoft tissue safety and complication risk depend on laser parameters and choice of technology. Reduced pulse powers maximize safety, instead pulse frequency seems safe to elevate for improved efficiency. At power levels beyond 20 W, Thulium:YAG benefited from longer pulses showing safer profiles, with shallower penetration and more reliable coagulation compared to Holmium:YAG.

Abstract from PubMed