In the clinical settings, factors like stone composition and location, lasering technique, retropulsion, precision, among many others affect the lithotripsy effectiveness. Instead, the in vitro studies allow a controlled environment for testing specific features. Evidently, outcomes from in vitro studies are not to translate into the clinical use but can certainly provide useful insight. The ablation rate, calculated as the mass of stone loss (mg) divided by the exposure time (s), is a practical estimate of effectiveness in vitro, where all other affecting factors are controlled as aforementioned. In this study,2 we analyzed the ablation rates of both TLF and Ho:YAG lasers using different setting combinations.
Flat disk-shaped BegoStones were lasered by a stepper motor bearing a 272 mm laser fiber conducting a preset computed spiral pattern. All experiments were conducted in a water container under continuous flow. Different combinations of frequency, pulse, and pulse width, for a total energy output of ~12 Watts (W) were compared between both Ho:YAG and TFL lasers. This was chosen based on the common settings used in clinical practice for ureteroscopy. Similarly, further 25 W combination for TFL were tested to analyze higher energy frequencies, one of the advantages attributed to the TFL.
The highest ablation rates were found when using 0.3 Joules (J), 40 Hertz (Hz), and Virtual Basketä emission mode with Ho:YAG and 0.3 J, 40 Hz and long pulse with TFL (114.35 [88.30 - 126.40] vs 143.40 [137.40 – 146] mg/min, p=0.057). Moreover, in the matching comparison for 1 J and 12 Hz, Ho:YAG and TFL showed comparable ablation rates for short pulse, otherwise the TFL outperformed Ho:YAG. Similarly, TFL outperformed Ho:YAG in the matching comparison using 0.3 J and 40 Hz. Of note, the Virtual Basketä emission mode significantly increased the Ho:YAG effectiveness, reaching ablation rates comparable to those of TFL. Further experiments were run to describe the ablation rate using higher frequencies and a total power output of 25 W with TFL. The highest ablation rate was found using 0.05 J and 500 Hz (155 [126 – 162] mg/min). Interestingly, even higher frequencies (1000 Hz) significantly dropped the ablation rate.
Overall, in this in vitro experiment, it seems as though TFL outperformed Ho:YAG using similar settings and total power outputs. Nevertheless, when using the Virtual Basketä emission mode in Ho:YAG, similar ablation rates to those of TFL were reached. Given the controlled scenario of in vitro studies, may be reasonable to hypothesized that the wavelength of TFL itself could be more efficient than the Ho:YAG and similar to that of the Ho:YAG with Virtual Basketä emission mode in vitro. Nonetheless, many other factors affect the effectiveness in the clinical scenario, and we must emphasize that this study is to provide insights into the ablation rates of both lasers and not to lead clinical decisions. Furthermore, a recent randomized controlled trial compared Ho:YAG modulated pulse laser to TFL and found no differences in the stone-free rate.3
As laser technology is advancing for both the Ho:YAG and the newer TFL, some surgeons might either jump into the hype of the newest TFL or stick to the well-known Ho:YAG, but we think one should be impartial, critical and evidence-based driven. Experienced surgeons may feel more comfortable with the Ho:YAG, that not only has been around for many years but has proven efficiency and safety and still ongoing improvements, however, the TFL has gained terrain and pushed the limits of laser lithotripsy technology, reporting great and faster dusting. Hence, both lasers are currently excellent choices for stone lithotripsy, and we are yet to understand their best role from warranted clinical trials.
Written by: Mario Basulto-Martínez1,2 Silvia Proietti2,3 Guido Giusti2,3
- Dept. of Urology, Hospital Regional de Alta Especialidad de la Península de Yucatán, Mexico.
- European Training Centre in Endourology, Milan, Italy
- Division of Urology, San Raffaele Hospital, Milan, Italy
References:
- Giusti G, Pupulin M, Proietti S (2022) Which Is the Best Laser for Lithotripsy? The Referee Point of View. Eur Urol Open Sci 44:20–22.
- Basulto-Martínez M, Proietti S, Pavia MP, et al (2023) Understanding the ablation rate of Holmium:YAG and thulium fiber lasers. Perspectives from an in vitro study. Urolithiasis 51:32.
- Haas CR, Knoedler MA, Li S, et al (2023) Pulse-modulated Holmium:YAG Laser vs the Thulium Fiber Laser for Renal and Ureteral Stones: A Single-center Prospective Randomized Clinical Trial. J Urol 209:374–383.