JU INSIGHT Comparative Analyses and Ablation Efficiency of Thulium Fiber Laser by Stone Composition

By: Jeffrey Johnson, MD, Weill Cornell Medicine, New York, New York; Justin Lee, MD, Columbia University Irving Medical Center, New York, New York; Miyad Movassaghi, MD, Columbia University Irving Medical Center, New York, New York; David Han, MD, Columbia University Irving Medical Center, New York, New York; Srinath-Reddi Pingle, MD, Columbia University Irving Medical Center, New York, New York; James Williams, PhD, Indiana University School of Medicine, Indianapolis; Michael Schulster, MD, Columbia University Irving Medical Center, New York, New York; Prakash Gorroochurn, PhD, Columbia University, New York, New York; Yinming Shao, PhD, Columbia University, New York, New York; Ojas Shah, MD, Columbia University Irving Medical Center, New York, New York | Posted on: 18 Mar 2024

Johnson J, Lee J, Movassaghi M, et al. Comparative analyses and ablation efficiency of thulium fiber laser by stone composition. J Urol. 2024;211(3):445-454.

Study Need and Importance

The thulium fiber laser (TFL) has rapidly become the laser of choice at many centers secondary to its ability to treat stones efficiently. Although discoveries are occurring rapidly with regards to its safety and efficacy, little is known regarding TFL lithotripsy by varying stone composition.

What We Found

We ablated 7 different common human stone types with 13 different laser settings ranging from 6 J × 2 Hz to 0.02 J × 2500 Hz including different pulse widths.

Across all settings and stone types 0.05 J × 1000 Hz, was the most effective ablation setting in s/mg/W. We then selected for safer clinical settings between 10 and 20W for renal stone settings. For these settings, calcium oxalate monohydrate ablated with the best numerical efficiency at 0.4 J × 40 Hz, short pulse; calcium oxalate dihydrate, cystine, and struvite at 0.2 J × 100 Hz, short pulse; uric acid and carbonate apatite at 0.3 J × 60 Hz, short pulse; brushite at 0.5 J × 30 Hz, short pulse (Figure).

Figure. Ablation efficiency of laser settings (y-axis) to stone composition (x-axis). Efficiency is represented in s/mg/W. Cell color within columns represent the numerically most efficient (green) to least efficient (red) settings. The bold, black borders represent the numerically most efficient ablation settings within clinically relevant settings of 10 to 20 W (bordered) for renal stones. Gray cells represent inadequately ablated specimens. CaPhos indicates calcium phosphate; COD, calcium oxalate dihydrate; COM, calcium oxalate monohydrate.

Electron microscopy analysis of cavities with char demonstrated a porous, melted microscopic structure. Fourier-transform infrared spectroscopy of charred stone types except brushite demonstrated wave numbers consistent with pre-ablation analysis; however, brushite demonstrated a chemical composition change to amorphous calcium phosphate.

Limitations

Several limitations of our study include its ex vivo design which may not extrapolate to in vivo conditions, and we only tested 13 laser settings (further study may elucidate a more optimal setting).

Interpretation for Patient Care

A practical application of these data could be to include TFL presets including 0.2 J ×100 Hz, short pulse, and and/or 0.4 J × 40 Hz, short pulse, as these 2 settings would provide the optimal laser settings for the most common stone types. We recommend using short pulse width in TFL lithotripsy to minimize charring and inadequate ablation.