The laser has become the preferred energy source for treating urinary stones, particularly in conjunction with ureteroscopy. Advances in laser technology over the past several years has allowed urologists to more efficiently and effectively fragment or dust stones. High powered holmium lasers with or without pulse modulation and the introduction of the thulium fiber laser (TFL) have allowed urologists to treat larger and more complex stones with laser lithotripsy. The question still remains, which should be the preferred energy source for laser lithotripsy?

The introduction of high-powered holmium lasers, generally defined as ≥ 60 W, has allowed for a greater variety of settings, most importantly for dusting, and increased frequency. With the holmium laser, lower energy settings have been demonstrated to produce the smallest fragments allowing for dusting.¹ High-powered holmium lasers can have energy settings as low as 0.2 J and frequencies as high as 100 Hz. The higher frequency on high-powered holmium lasers allows for faster dusting. When comparing dusting efficiency between a 120 W holmium laser and a 20 W holmium laser, Mekayten and colleagues found a greater than 50% reduction in lasing time with the 120 W laser.² The advent of pulse modulation for holmium lasers has further improved efficiency in laser lithotripsy. Pulse modulation, including Moses Technology available on the Boston Scientific P120 laser system (Boston Scientific, Marlborough, Massachusetts) and Vapor Tunnel and Virtual Basket available on the Quanta Litho 150 (Cook Medical, Bloomington, Indiana), allows for decreased stone movement and improved dusting efficiency. Both clinical and benchtop studies have demonstrated improved efficiency when compared to standard holmium pulse widths.^3,4

More recently, the TFL lasers have been introduced to the market. These lasers provide an even greater variety of laser settings, with energies as low as 0.05 J and frequencies as high as 2,000 Hz. Benchtop studies have shown that the TFL laser produces finer dust and is more efficient at creating dust than holmium lasers, with or without pulse modulation.^5,6 This effect is likely due to the longer pulse duration and lower peak power seen with TFL lasers. In addition to improved dusting efficiency in vitro, there are other potential advantages of the TFL laser over high-powered holmium. The units are generally smaller, quieter, and do not require special power outlets.

Clinical studies have demonstrated improved outcomes for the TFL compared to the holmium laser. Most recently, Ulvik and colleagues performed a prospective, randomized trial comparing a THL laser with a 30 W holmium laser for the treatment of intrarenal stones and ureteral stones.⁷ This trial utilized a dusting technique for intrarenal stones and fragmenting for ureteral stones. The stone-free rate was determined with noncontrast computed tomography at 3 months. For intrarenal stones, TFL performed significantly better than holmium, with a stone-free rate of 86% vs 49%. However, for ureteral stones both lasers had a 100% stone-free rate. They reported reduced mean surgical time with the TFL laser as well, 49 minutes vs 57 minutes. The primary limitation in this trial is it utilized a low-powered holmium laser, which is a disadvantage when it comes to dusting intrarenal stones. High-powered holmium lasers have been shown to be more efficient at dusting stones than lower-powered holmium lasers.

Ultimately the debate regarding holmium lasers vs TFLs may be similar to the debate regarding lithotripsy technique, dusting vs basketing. Studies have demonstrated similar clinical outcomes whether intrarenal stones are treated with dusting or fragmentation with basket extraction.⁸ Each technique has its advantages and disadvantages. The discussion has turned from which technique is better to what is the right way to approach each stone, given stone-related factors and patient-related factors. For most urologists, both dusting and fragmentation with extraction each have a role in their practice. The same will likely be true for holmium and TFL. Early evidence suggests TFL is more efficient at dusting, but there is evidence to suggest holmium is more effective and efficient at fragmentation.⁹ This is due to the shorter pulse width and higher peak power of the holmium laser.

It will be incumbent on urologists to determine what the optimal scenarios to utilize holmium vs TFL lasers are in the future. It may be that if the preferred treatment is to dust, for instance with larger intrarenal stones, the TFL laser will be preferred (Figure 1). In cases where fragmentation and extraction are preferred or indicated, the holmium laser may be preferred (Figure 2). In order to take the best care of our patients it may be that urologists will need access to both lasers in the future.