Comparison of Superpulse Thulium Fiber Laser vs. Holmium Laser for Ablation of Renal Calculi in an In Vivo Porcine Model - Andyshea Afyouni
August 26, 2022
Andyshea (Andrew) Afyouni, MD Candidate, Department of Urology, University of California, Irvine
Andrew Afyouni: Percutaneous nephrolithotomy, or PCNL, has long been the gold standard for the treatment of renal stones greater than 2 centimeters. Recently, there have been significant technological advancements in ureteroscopy, opening the door to the possible treatment of renal stones two centimeters and larger. Specifically, the Superpulse Thulium Fiber Laser has emerged as a competitor to the holmium laser, given its promise of a superior ability to render a stone into spontaneously passable dust fragments. The Superpulse Thulium Fiber Laser operates at a wavelength of 1940 nanometers, which corresponds with the peak wavelength for energy absorption by water. Additionally, the Thulium laser is effective at very low energies due to its ability to achieve very high repetition rates, upwards of 2000 firings per second. This arrangement of low power and high repetition rates may favor finer fragmentation or dusting of stones.
In this study, we sought to evaluate the effectiveness and efficiency of the Superpulse Thulium Fiber Laser versus the standard Holmium laser for ureteroscopic dusting of renal stones in an in vivo porcine model. 24 kidneys from 12 juvenile female Yorkshire pigs were randomized to either Holmium or Thulium treatment groups. Canine calcium oxalate stones were scanned with a CT scanner to calculate stone volume and stone density. The stones were randomized and implanted into each renal pelvis via an open pyelotomy. Stones were further advanced within an upper pole calx and sutures were subsequently closed. Retrograde flexible ureteroscopy was performed within 9.9 French Wolf dual lumen ureteroscope via a 14 French, 35-centimeter ureteral access sheath.
Two percutaneously placed K-type thermocouples were passed into the kidney, one in the stone-bearing calyx and one in the renal pelvis. Laser lithotripsy was performed with both the Holmium and the Thulium laser at 16 Watts. For the Holmium laser, the setting was 0.4 joules and 40 Hertz transmitted via a 272-micron fiber. For the Thulium laser, the setting was 0.2 joules and 80 Hertz transmitted via a 200-micron fiber. Lithotripsy was performed through the dual lumen ureteroscope with the laser fiber passed via one channel and irrigation flowing via the second channel. Lithotripsy continued until it was agreed upon by two urologists that no fragments over 1 millimeter remained. No stone basketing or attempts at aspiration of fragments was performed.
Next, the ureteropelvic junction, or UPJ, was ligated and the kidneys were bi-valved and irrigated to collect any residual fragments. The collected fragments were dried, after which they were weighed and then measured with an optical laser particle size.
There were no differences between the two groups with regard to the volume or density of the implanted stones. Of note, maximum temperature reached during lithotripsy in the renal pelvis and in the stone-containing calyx was 37 and 40 degrees Celsius respectively. This was similar for both the Holmium and Thulium laser. Stones treated with Thulium laser lithotripsy were ablated three times faster than with the Holmium laser, 9 minutes versus 27 minutes respectively. The Thulium laser used three-fold less energy to ablate the stones, 8 kilojoules versus 26 kilojoules for the Holmium laser. Thulium lithotripsy had a higher stone clearance rate of 73% versus 45% for the Holmium laser. Furthermore, the Thulium laser had a three-fold greater stone dusting efficiency, with an average of 53 millimeters-cubed per minute versus 17 millimeters-cubed per minute for the Holmium laser.
After Thulium lithotripsy, 77% of the residual fragments were less than 1 millimeter, versus only 17% for the Holmium laser. Finally, 23% of residual stone fragments created by Thulium lithotripsy were in the 1 to 3-millimeter range and only 1% of fragments were greater than 3 millimeters, versus 68% and 15% respectively for Holmium laser lithotripsy.
In conclusion, in an in vivo porcine model with canine-derived calcium oxalate stones of similar volume and density, the Superpulse Thulium Fiber Laser resulted in significantly greater stone clearance rates, shorter ablation times, greater lithotripsy efficiency, and smaller stone fragments. Thank you.