Introduction
Urinary tract stones are commonly treated by laser, and Ho: YAG (Holmium: Yttrium-aluminum garnet) is the standard laser used. In this article, the outcomes of a newly emerging treatment that is thulium fiber laser, are discussed.
What Is a Thulium Fiber Laser?
Thulium fiber laser uses small laser fibers. Retropulsion rates are less when compared to Ho: YAG laser, and stone ablation rates are faster. It has better safety and machine form factor.
What Are the Advantages of a Thulium Fiber Laser Compared to Ho: Yag?
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Safety: No preferred anatomic location; residual fragments are smaller, resulting in fewer basketing passes, and unintended laser damages are lesser because of better visibility. Thulium fiber laser has resistance against bending diameters. The flexible scopes have laser emission, which helps in avoiding breakage. An additional safety measure is present because of optimal and clear visibility, which helps judge a better tip position during surgery. This helps to reduce unintentional damage to the surrounding tissues. There may be issues of temperature rise, which may lead to ureteral stenosis; some authors have named it as thermal effect of thulium fiber laser. Authors have suggested that these problems arise due to inefficient irrigation, which can be compensated by better irrigation techniques, laser activation, and cooled irrigation.
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Visibility: Decreased visibility in high frequency, greater than 200 Hz. Optimum visibility in most cases.
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Laser Fibers: Energy resistant, flexible and small fibers. The laser fibers are the size of 150 μm, have lesser burnback, are resistant to bending, and are more flexible when compared to Ho: YAG laser. Thulium fiber lasers having a small diameter produce smaller stone fragments and also produce higher ablation volumes; because of the smaller diameter, there is higher energy density. It has better instrument deflection and helps tackle larger stones through retrograde intrarenal surgery. Hence thulium fiber laser helps in the enhancement of these surgeries in the removal of large kidney stones.
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Temperature Safety: No difference noted.
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Retropulsion: Retropulsion is reduced or maybe even absent according to recent clinical studies (ureteroscopy and percutaneous nephrolithotomy) and in vitro. Stone retropulsion threshold is four times higher at equal pulse energies with a thulium fiber laser. Retropulsion for thulium fiber laser is at 1 Joules pulse energy, and for Ho: YAG is around 0.2 Joules pulse energy. The reason is lower peak power and constant prolonged peak power, with longer pulse duration without any difference in ablation efficiency. Thulium fiber laser produces 95 % better visibility.
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Dust and Residual Particles: Thulium fiber laser produces a larger quantity and a finer dust quality. Dust fragments are smaller, but the quantity produced is higher than Ho: YAG. Thulium fiber lasers have a four to fivefold higher dusting rate. The particles are different from those resulting from Ho: YAG. Compared to Moses technology, it provides twice as much dust and can provide stone dust from all types of stone. The mean stone particle size is less than 1 mm to 0.5 mm. According to a study, the largest residual fragments had 116 to 254 m in size, depending on the stone composition. There is an advantage of fewer basketing passes when the particle size is small, which helps reduce complications and operating room time.
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Machine Specifications: Produces power up to 500 W and pulse frequency up to 2400 Hz. Pulse durations are smaller and lighter. Produces low pulse energies of 0.2 to 0.6 Joules. It can be connected to any standard power outlet. Thulium fiber lasers use electronically modified laser diodes, whereas Ho: YAG lasers use flash lamps. Thulium fiber laser offers a wide range of laser parameters, such as its capacity of constant and higher peak power. The laser generator produces a small core laser fiber called the gain medium, hence the fiber laser. The resonance chambers consist of laser rods in the Ho: YAG laser case. These laser rods have complex precision alignment and optical systems. The laser radiation of Ho: YAG laser is 2100 nm wavelength, and that of thulium fiber laser is 1940 nm wavelength. Thulium fiber laser has high efficiency towards any type of urinary calculi because of its high radiation absorption. It is four times higher than water.
The recent innovation of thulium fiber laser has the power of attaining a peak value of 500 W and can emit up to 6 Joules starting from small pulse energy of 0.025 Joules. Out of all these advantages, the thulium fiber laser has an extraordinary pulse frequency ranging up to 2000 Hz. The latest models show a pulse frequency up to 2400 Hz, whereas the Ho: YAG laser has a pulse frequency of 120 Hz. Ho: YAG lasers cannot work in higher frequencies, longer pulse durations, and very low pulse energies. Thulium fiber lasers can work under both long pulse durations and low pulse energies, and these hold a great advantage over Ho: YAG lasers.
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Ablation Efficiency: Fragmentation settings of thulium fiber laser ablate two times faster, and the dust settings ablate four to five times faster. Thulium fiber laser shows more efficiency towards urinary calculi and has superior lithotripsy performance three times that of Ho: YAG lasers. The better performance of the thulium fiber laser can be attributed to its four times higher performance in wavelength absorption in water and steady and prolonged power peak levels which provides humongous thermomechanical interactions and photothermal effects.
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Optimal Settings: These may be the best settings, according to some authors, for thulium fiber laser, such as 1 to 1.5 Joules and 15 to 30 Hz for fragmentation, for dusting (micro) PCNL is 50 to 100 W and 0.1 to 0.3 Joules, 0.1 to 0.2 Joules in kidney for dusting,0.2 to 0.5 Joules for 10 to 15 W for dusting and fragmentation in the ureter. For bladder stone treatment, it is 2 to 5 Joules and 5 to 10 Hz; for upper tracts, 500 Hz is given by reports suggested by authors.
Conclusion
Based on the studies conducted compared to Ho: YAG laser, thulium fiber laser shows promising results and has great potential to replace Ho: YAG lasers. The complete transition of Ho: YAG laser to thulium fiber laser may not be easy as it requires further studies about the availability and usage of thulium fiber laser machines.
