The holmium:YAG laser has been the gold standard intracorporeal lithotripter for ureteroscopy for approximately the last 20 years. Its ability to fragment stones of all compositions coupled with a wide margin of safety led to its rapid adoption after its introduction. Refinements over the years including higher pulse frequency settings, the ability to increase the pulse duration and pulse modulation have helped extend the life of the platform. However, inherent limitations of the technology related to the high power requirements and extensive cooling systems appear to have placed a ceiling on future significant improvements.

Figure. Soltive™ dusting settings.

The introduction of the super pulse thulium fiber (SPTF) laser (Soltive™, Olympus Surgical, Southborough, Mssachusetts) to the North American and European markets has resulted in a true viable alternative to the holmium:YAG platform for stone and soft tissue treatment. The SPTF laser is a simplified design compared to the multirod holmium:YAG systems. It consists of a thulium doped fiber that is activated by a diode laser. It emits at a 1,920 nm wavelength that is even more highly absorbed in water as compared to the 2,140 nm wavelength of the holmium:YAG. The laser is small and portable, but perhaps more critically it uses standard electrical power and can be plugged into a standard electrical outlet. This is in contrast to the high power holmium:YAG systems, which require dedicated 20 to 50 amp service depending on the model. The 1,920 nm wavelength of the SPTF laser may be a more efficient wavelength to treat stones, and it can be used with laser fibers with core diameters as small as 50 microns. The multimodal holmium:YAG beam does not couple well with fibers with core sizes less than 240 microns, thereby limiting the ability to use smaller fibers. While these properties of the SPTF laser position it well as a successor to the holmium:YAG laser, in endourology the biggest advantage it has over existing holmium:YAG systems is its ability to deliver the laser pulses at an ultrahigh frequency of up to 2,400 Hz.

Early holmium:YAG systems were limited to pulse frequencies of 40 Hz. Later development allowed the most advanced systems to reach 80 to 100 Hz. As pulse frequency capabilities improved, the concept of performing laser lithotripsy with “dusting settings,” where low pulse energy delivered at high pulse frequency, became in vogue (see figure). Low pulse energy allows for the creation of smaller stone fragments but increases the time it takes to break up the entire stone since such small pieces are chipped off the stones. Higher pulse frequency settings will speed the process but the upper limit of the holmium:YAG is quickly reached. The SPTF laser is not limited by the pulse frequency setting. While 0.2 to 0.3 J pulse energy settings at 50 to 80 Hz (10 to 24 watts) are typically used with the holmium:YAG for “dusting,” with the SPTF laser pulse energy can be set lower such as at 0.05 Hz,with the goal to create very tiny dust-like fragments. The pulse frequency can be increased to compensate for the low pulse energy. For example, the pulse frequency can be increased to 300 Hz, 3 times greater than the most advanced holmium:YAG systems, while still maintaining a wide margin of safety with only 15 W of power output. The reality is that 300 Hz is just scratching the surface of what the system is capable of, with the Soltive Premium maxing out at 2,400 Hz.

Many have speculated that there are diminishing returns with higher frequencies. At this time I would simply say “maybe.” The SPTF laser is being used with endoscopes and other equipment that were designed for the holmium:YAG era. We must now begin to think about how we can make our other tools better to leverage the capabilities of the SPTF laser. It should be an exciting decade ahead as we see this develop.