(UroToday.com) The 2022 World Congress of Endourology and Uro-Technology (WCET) annual meeting included a moderated poster presented by Andrew Afyouni from the University of California, Irvine Department of Urology investigating differences between the efficacy and effectiveness of the superpulse thulium fiber laser versus the conventional holmium fiber laser for ureteroscopic dusting of renal stones.
For the longest time, percutaneous nephrolithotomy, or PCNL, has reigned as the “go-to” therapy for treatment of renal stones greater than 2 centimeters. However, more recently, there have been significant technological advancements in how surgeons perform ureteroscopy, opening the door to the possible treatment of renal stones two centimeters and larger. One such advancement has been the advent of the Superpulse Thulium Fiber Laser, which has quickly 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 Thulium Fiber Laser has been shown to operate at a wavelength of 1940 nanometers, which corresponds with the peak wavelength for energy absorption by water. Furthermore, the Thulium laser has been shown to be effective at very low energies due to its ability to achieve very high repetition rates, equating to rates upwards of 2000 firings per second. This arrangement of low power and high repetition rates has been shown to favor finer fragmentation, or what is known as “dusting” of stones.
In this study, Andrew Afyouni evaluated differences in performance between the thulium and holmium laser in an in-vivo porcine model with canine calcium oxalate stones. To achieve this end, Afyouni and colleagues first randomized and then implanted stones of known stone density and volume into the renal pelvis of 24 kidneys from 12 juvenile female Yorkshire pigs via an open pyelotomy. Stones were further advanced within an upper pole calyx and sutures were subsequently closed. (Figure 1) Following this, the team performed retrograde flexible ureteroscopy via a 9.9 French Wolf dual lumen ureteroscope and a 14 French, 35-centimeter ureteral access sheath.
The team was meticulous to also monitor temperature changes in the renal calyces and pelvis during lithotripsy by inserting two percutaneously placed K-type thermocouples. 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 200-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.
To extract all residual stones left following lithotripsy and accurately assess the extent of stone fragmentation, they were sure to not perform any stone basketing or attempt to aspirate any fragments during each procedure. Stone extraction was achieved by first ligating the ureteropelvic junction (UPJ) to ensure no fragments escaped and kidneys were then bi-valved and irrigated to collect any residual fragments. The collected fragments were dried, then weighed, and finally measured with an optical laser particle size.
The results of the study were multifold. First, it was determined that there were no differences between the Thulium and Holmium groups with regard to the volume or density of the implanted stones. Temperature readings of the K-type thermocouples further demonstrated that 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, thus showing that neither laser exceeded the established threshold of renal parenchymal damage typically seen at temperatures of 44 degrees Celsius or higher. (Figure 2)
Next, the authors showed that stones treated with Thulium laser lithotripsy were ablated three times faster than with the Holmium laser, with ablation times of 9 minutes versus 27 minutes, respectively. Furthermore, the Thulium laser was found to use three-fold less energy to ablate the calcium oxalate stones with an average energy output of 8 kilojoules versus 26 kilojoules for the Holmium laser. Additionally, Thulium lithotripsy was shown to have a higher stone clearance rate of 73% versus 45% for the Holmium laser and also 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. (Table 1)
Finally, it was determined that, after Thulium lithotripsy, 77% of the residual fragments were less than 1 millimeter, versus only 17% for the Holmium laser. It was also found that 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. (Table 2)
Overall, Afyouni and colleagues were able to show that the Superpulse Thulium Fiber Laser resulted in significantly greater stone clearance rates, shorter ablation times, greater lithotripsy efficiency, and smaller stone fragments in this in-vivo porcine model.
Presented by: Andrew S. Afyouni, BS, Medical Student, Department of Urology, University of California Irvine
Written by: Andrew S. Afyouni, BS, Medical Student, Department of Urology, University of California Irvine, @AndysheaAfyouni on Twitter during the 39th World Congress of Endo urology and Uro-Technology (WCET), Oct 1 - 4, 2022, San Diego, California.