Laser technology is one of the most significant novelties that has been introduced in endourology. Since its introduction in the late 1980s, the holmium (Ho):YAG laser has gained popularity among urologists and has been considered the gold standard laser for lithotripsy for the last 30 years, thanks to its capabilities and safety profile.¹

Similar to most technological developments, laser lithotripsy has also improved with recent advancements in terms of power, pulse modulation, and new laser technologies. As a result, the use of high-power Ho laser machines has increased, with new generation systems that allow the selection of several parameters, such as pulse energy, frequency, pulse width, and modulation that can optimize and improve the efficiency of laser lithotripsy.²

On the contrary, the thulium fiber laser (TFL) has recently emerged as an alternative in laser lithotripsy,³ with an ever-growing dissemination among the urological community because of its supposed better dusting capability that has led some clinicians to regard it as a game changer, even though robust clinical evidence is still lacking.

Several in vitro studies have demonstrated superiority of TFL over Ho:YAG lasers, being more efficient and faster in terms of stone ablation.⁴ Anyway, recently, it has been shown that the Virtual Basket emission mode increased Ho:YAG ablation rates, reaching similar results to those of TFL in certain modalities.⁵

In truth, when TFL was introduced in the clinical scenario, the outstanding expectations about TFL were, at least in part, disregarded. The initial settings using very low energies and very high frequencies, evaluated in in vitro studies, were not as efficient in vivo as previously postulated, leading urologists to shift to clinical TFL settings almost similar to those used for Ho:YAG laser.

Probably, as supposed by Ghani, experiments with TFL, which is a contact laser, were performed in an optimal environment for its physical features with the fiber always in contact with the phantom stones and with the laser continuously activated.⁶ This is completely different in real life where it is really challenging to be always in contact with the stone. In addition, the laser firing may be intermittent because of impaired vision due to the presence of huge amounts of floating dust and in order to minimize the intrarenal temperature. In contrast, stone ablation with Ho:YAG laser can occur at 1-2 mm away from the tip, overcoming the aforementioned difficulties during lithotripsy.⁷

In a randomized clinical trial, Ulvik et al demonstrated the higher efficacy and safety of TFL compared to Ho:YAG laser for the treatment of ureteral and renal stone.⁸ But some biases are present in this study, such as surgeons’ variability, unusual laser settings used, and, most importantly, the comparison with low-energy old Ho:YAG laser. As said in my previous editorial on this issue, it is like comparing a Tesla Roadster with a Fiat Panda instead with a Ferrari to demonstrate the superiority of an electric engine over a thermic one: it is quite counterintuitive!⁹

Conversely, in another recent randomized clinical study that finally compared advanced high-powered pulse-modulated Ho:YAG laser vs TFL, Haas et al suggested no significant clinical advantage of one laser technology over the other. They stated that surgeon and institutional preference are the best approach when selecting one or the other.¹⁰

Surely, TFL has better results in reducing stone retropulsion. As reported by Traxer¹¹ and Ventimiglia¹² et al, this can be clarified by different laser pulse shapes, prolonged peak power levels, and higher water absorption that lead to minimum turbulence in the field. The TFL has a lower peak power than the Ho:YAG laser. This is advantageous in stone retropulsion reduction, but it is less useful in fragmentation, especially in minipercutaneous nephrolithotomy, whose quintessence is benefiting from the vacuum cleaner effect that perfectly works in tandem with the stone fragmentation.

Controversial are the laboratory results on intrarenal temperatures generated by the TFL in comparison with the Ho:YAG laser at the same power settings.¹³ Nevertheless, no clinical data are available on this issue, and this is a concern that really deserves more investigations to better define the safety profile of both lasers.

TFL generates a more uniform and focused laser beam that can be transmitted by smaller core diameter laser fibers (50–150 μm), whereas Ho:YAG laser can only safely use fibers with a core diameter >200 μm. This translates to better irrigation through the working channel, better scope deflection, and possible further scope miniaturization in favor of TFL.¹⁴

In addition, there is no doubt about the superior ergonomics of TFL. The TFL’s machines are smaller, lighter, cheaper, more environmentally friendly, durable, and noiseless than the Ho:YAG lithotripters.⁴ Moreover, TFL laser becomes essential when 2 lasers are needed during simultaneous bilateral surgery such as mini-simultaneous bilateral endoscopic surgery, as usually only 1 single high-amperage plugging system per operating room is available.¹⁵

With that said, endourologists should also keep in mind that, according to the famous adage by Spider-Man, “With great power comes great responsibility.” This huge power should be delivered carefully and not always entirely used only because it is available; otherwise, inevitable consequences may develop in all stone-containing organs.¹⁶ In other words, if on one hand these huge advancements in laser technology are supposed to improve outcomes of retrograde intrarenal surgery and to broaden indications to this endoluminal approach, on the other hand, being that complete dusting of big stones is still far away from real practice, it would be a great mistake to use these newer technologies to deliver the misleading concept that retrograde intrarenal surgery is a sort of panacea for all stones including big staghorn ones in order to abandon the more invasive but also more effective percutaneous nephrolithotomy for this subset of patients.

Tailored surgery is still here to stay, always offering the best solution for every patient and stone. Accurately planning the procedure preoperatively is of uttermost importance, but likewise, it is crucial to always be ready to change the endourological strategy along the way if needed without having to always choose flexible ureteroscopy because of the super efficiency of the available laser, or worse, because of the lack of percutaneous nephrolithotomy skill as frequently happens around the world. Mini-invasiveness is real progress only when it matches with similar outcomes and safety.

In conclusion, the topic is really intriguing and the level of our distinguished opponents is so high that this debate is a real, not to be missed event worth attending live. Please join us in great numbers and you won’t regret it!

Conflicts of Interest

Dr Giusti is a consultant for Rocamed and Quanta System.