Thulium fiber laser: ready to dust all urinary stone composition types?

Purpose: To evaluate whether stone dust can be obtained from all prevailing stone composition types using the thulium fiber laser (TFL) for lithotripsy. Where applicable, stone dust was further characterized by morpho-constitutional analysis.
Methods: Human urinary stones were submitted to in vitro lithotripsy using a FiberLase U2 TFL generator with 150 µm silica core fibers (IPG Photonics ^® , IPG Medical™, Marlborough, MA, USA). Laser settings were 0.05 J, 320 Hz and 200 μs. A total of 2400 J were delivered to each stone composition type. All evaluated stones had a > 90% degree of purity (calcium oxalate monohydrate, calcium oxalate dihydrate, uric acid, carbapatite, struvite, brushite and cystine). Spontaneously floating stone particles were considered as stone dust and collected for analysis by scanning electron microscopy and Fourier transform infrared spectroscopy.
Results: Stone dust could be retrieved from all evaluated urinary stones after TFL lithotripsy. Most stone dust samples revealed changes in crystalline organization, except for calcium oxalate monohydrate and carbapatite, which conserved their initial characteristics. Mean maximal width of stone dust particles did not exceed 254 µm.
Conclusions: The TFL is capable to produce stone dust from all prevailing stone types. Morpho-constitutional changes found in stone dust suggest a photothermal interaction of laser energy with the stone matrix during TFL lithotripsy.