Two categories of lasers can be distinguished in urology: continuous lasers and pulsed lasers. While continuous lasers are used exclusively for tissue applications, pulsed lasers, which are more versatile, can be used both for tissue applications and for lithotripsy.¹ The pulsed lasers currently used for the latter indication are Ho:YAG, thulium fiber laser (TFL), and pulsed Tm:YAG (pTm:YAG).

Among Ho:YAG lasers, low-power lasers (30 W) can be distinguished from high-power lasers (>100 W). These lasers have the same energy levels and therefore the same effects during lithotripsy, but differ in their ability to reach high frequencies (50-80 Hz) with high-power systems. Finally, laser pulse modulations have appeared in order to improve Ho:YAG performance (Moses Technology, Virtual Basket, Vapor Tunnel, Bubble Blast, and Magneto).

Four questions can be asked in order to determine which laser is the best for lithotripsy:

1. Which one provides the best efficacy for ureteroscopy, percutaneous nephrolithotomy (PCNL), and cystolithotripsy?
2. Which one is the best for dusting/fragmentation?
3. Which one has the lowest retropulsion?
4. Which one is safer?

Which One Provides the Best Efficacy for Ureteroscopy, PCNL, and Cystolithotripsy?

When the 3 pulsed lasers are compared in in vitro lithotripsy testing, TFL and pTm:YAG appear to have similar efficacy, whereas Ho:YAG shows lower performance.^2,3 However, does this translate into clinical practice? This is what we will address.

Ureteroscopy

The meta-analysis by Uleri et al,⁴ comparing TFL and Ho:YAG during retrograde intrarenal surgery, found a significant advantage in favor of TFL for the treatment of renal stones in terms of stone-free status (odds ratio [OR] = 3.14 [1.69, 5.86]) and zero residual fragments (OR = 2.99 [1.50, 5.97]). However, this difference disappeared when Moses Technology was used with Ho:YAG laser. For ureteral stones, no difference between the 2 lasers was observed. Finally, operative time favored TFL (OR = −3.71 [−7.40, −0.03]). Regarding pTm:YAG, a single nonrandomized clinical study compared it with TFL during retrograde intrarenal surgery and found a similar stone-free rate but a better zero residual fragments rate in favor of TFL.⁵

PCNL

For PCNL, the meta-analysis of Uleri et al⁴ demonstrated similar stone-free rates between TFL and Ho:YAG.

Cystolithotripsy

An in vitro study compared procedure times between TFL and Ho:YAG lasers (low and high power, with and without Moses Technology) for 4-cm synthetic stones. High-power Ho:YAG (120 W) with Moses Technology achieved the shortest lithotripsy time (68.3 minutes), whereas TFL took 261.4 minutes and low-power Ho:YAG (30 W) took 297.5 minutes.

Which One is the Best for Dusting/Fragmentation?

In vitro studies, using synthetic stones, showed that TFL produces 4 times more dust, defined as stone fragments < 250 µm, than Ho:YAG using Moses Technology.⁶ These findings were confirmed by another in vitro study by Chew et al.⁷ This study further reported that Moses Technology produced a trend toward smaller fragments compared with long-pulse Ho:YAG. Finally, a study showed that TFL was capable of producing stone dust from all human stone types.⁸ Similarly, pTm:YAG was shown to produce stone dust from all human stone types, with a low count of particles > 250 µm. However, a limitation of this study is that it was not comparative.

Although the dusting technique is becoming increasingly prevalent in ureteroscopy, fragmentation regimens remain important when

• Performing laser stone treatment for kidney stones during standard PCNL and mini PCNL.
• Ureteroscopic management of impacted large ureteral stone burden is needed.
• Cystolithotripsy for bladder stones is needed.

For these indications, Ho:YAG remains the reference laser.

Which One Has the Lowest Retropulsion?

Ventimiglia et al⁹ showed in an in vitro study that TFL has the lowest retropulsion compared with Ho:YAG, regardless of pulse duration (short or long pulse) or the use of Moses Technology. Another study comparing Ho:YAG and pTm:YAG demonstrated an advantage for pTm:YAG regarding retropulsion.¹⁰ Unfortunately, this laser has not yet been compared with TFL.

Which One Is Safer?

Recent concerns have been raised regarding the safety of lasers and the potential risk of ureteral stricture following ureteroscopy.¹¹ Ureteral strictures have been reported in up to 3% of patients after the procedure. One of the mechanisms underlying stricture formation is thermal injury caused by the laser. Such injury can induce inflammatory processes within the ureteral wall, ultimately leading to stricture formation.

Thus, the influence of laser technology on the risk of ureteral stricture has been investigated. Studies have shown that, regardless of the laser type used (Ho:YAG, TFL, or Tm:YAG), similar temperature increases occur when equivalent power settings are applied. Therefore, the key determinant appears to be the average power delivered by the laser generator rather than the laser type itself.

In conclusion, each laser modality has its own advantages and limitations, and none currently provides a unanimous answer to all questions addressed in this article. As is often the case, the choice ultimately represents a balance between performance criteria. Whether future technological developments will lead to the emergence of a truly universal and polyvalent laser remains uncertain—only time will tell.