Abstract and Introduction
Purpose of Review: To present the evidence of latest developments of lasers for the surgical treatment of benign prostatic hyperplasia (BPH). We focused on recent advancements in Ho:YAG laser such as Moses technology, the Thulium Fiber Laser (TFL), the blue diode laser, and hybrid laser.
Recent Findings: Laser enucleation of prostate techniques using either Ho:YAG laser with the Moses technology and Moses 2.0, or TFL seem efficient and safe compared with the standard enucleation using Ho:YAG laser. Only in vitro studies evaluated the blue diode laser and hybrid laser (combination of a continuous wave TFL and blue diode laser). Blue diode laser showed intermediate incision depth and minimal coagulation depth compared with Ho:YAG laser and Super Pulse TFL. Hybrid laser showed deep incision depth and small coagulation area compared with Ho:YAG laser and continuous wave TFL.
Summary: Surgical treatment of BPH using Moses technology, Moses 2.0, and TFL shows encouraging results comparable to the standard enucleation using Ho:YAG laser. Only in vitro data are currently available for blue diode laser and hybrid laser. Future well-designed studies comparing these technologies and evaluating them on specific risk groups of patients as well as the long-term durability of outcomes are needed.
Lasers are currently integral part of the armamentarium in endourology and can be used for many indications such as lithotripsy, ablation, vaporization, resection and enucleation of prostate, treatment of urothelial tumors, endopyelotomy, incision of ureteral strictures.[1–3] Since its introduction in the 1990s, the Holmium: yttrium aluminum garnet (Ho:YAG) laser, which emits at a wavelength of 2120 nm, became the reference of lasers in urology because of its versatility, and efficiency.[3,4] Since then, refinements and other laser technologies have emerged. Currently, laser technologies play a prominent role in modern endoscopic management of benign prostatic hyperplasia (BPH). Holmium laser enucleation (HoLEP) has been the most widely used treatment option for decades.[3,5,6] Recently, increasing variety of lasers with different wavelengths and optical power have been developed and applied in BPH surgery. In this review, we aimed to provide evidence of latest developments of lasers for the surgical treatment of BPH. We focused on recent advancements in Ho:YAG laser such as Moses technology, the Thulium Fiber Laser (TFL), the blue diode laser, and hybrid laser.
Holmium: Yttrium Aluminum Garnet Laser and Moses Technology
Use of the Ho:YAG laser in prostate surgery was first described in 1996 for holmium laser resection of the prostate, and has become nowadays a standard tool in BPH surgery.[3,5–8] The Ho:YAG laser operates at a wavelength of 2120 nm in a pulsed mode. At this wavelength, the water optical absorption coefficient is 25 cm−1, which is near its absorption peak. This means laser energy is highly absorbed in water.[9–11] Thus, the tissue penetration depth is 0.4 mm and leads to a high energy density delivery at the tissue surface. Whereas most advancements in Ho:YAG laser technology were focused on increase in power output, a pulse modulation technology, called "Moses Technology", was introduced in 2017. The laser pulse with Moses technology is divided into two parts: the first one is only used to create a vapor bubble to separate the water between the laser tip and the target, whereas the second directly delivers the rest of energy through this vapor bubble toward the target. This increased energy delivery has been hypothesized a better enucleation efficiency, with more tissue ablation and separation, allowing an easier surgical plane dissection due to the pulse shape, and a better hemostasis. Recent clinical studies evaluated the results of Moses technology during BPH surgery.
In a retrospective study, Whiles et al. compared the results of holmium laser ablation of the prostate (HoLAP) with or without the use of Moses technology. The authors reported that ablation time was similar between groups but ablation efficiency (grams ablated/minute) was increased with the use of Moses technology (0.91 ± 0.54 g/min without vs 1.77 ± 1.41 g/min with Moses technology). Catheterization time, length of hospital stay, and short-term postoperative complications or reoperation rates were similar between groups. Both groups had comparable improvements in functional outcomes (IPSS, quality of life (QoL), and postvoid residual volume (PVR)) at 3 months.
In a prospective double-blind, randomized controlled trial, Kavoussi et al. compared the outcomes of HoLEP with and without Moses technology. They included patients with prostate volumes larger than 80 mL. Mean enucleation and hemostasis times were 12 and 11 min shorter with the use of Moses technology. Postoperative change in hematocrit was significantly less for the Moses technology group. The authors did not report any difference in intraoperative energy utilization, estimated blood loss, nor prostate tissue removed. Catheterization time, length of hospital stay were similar between groups. Both groups had comparable improvements in functional outcomes (IPSS, QoL, uroflow measurements, and PVR) as well as change in PSA, and complication rates. A prior retrospective study found comparable outcomes.
Recently, the second generation of Moses technology, called "Moses 2.0" has been released. According to the manufacturer, this Moses 2.0 is an optimized Moses pulse and allows the use of high frequencies > 80–120 Hz, which was not the case with the previous version (80 Hz maximum). This new pulse modulation was developed with the intent to optimize HoLEP with a better cut and hemostasis. However, currently there is no in vitro data comparing the Moses technology and Moses 2.0 on their technical characteristics (pulse duration, vapor bubble shape) and tissue effects.
In a prospective double-blind, randomized controlled trial, Nevo et al. compared the outcomes of HoLEP with and without Moses 2.0. During HoLEP, the Moses 2.0 was used for one prostate lobe enucleation, and the second lobe was performed with a standard mode. The authors did not report any difference between the right and left lobe with respect to enucleation time, enucleation efficiency, total energy, enucleation laser energy, and hemostasis laser energy used. In a subgroup analysis, the use of Moses 2.0 resulted in shorter enucleation time (21 vs 36.7 min) and higher enucleation efficiency (1.75 vs 1.05 g/min) than the standard mode when procedures were performed by experts. A shorter hemostasis laser time was found with the use of Moses 2.0 when procedures were performed by trainees.
In a retrospective study, Nottingham et al. reported a shorter hemostasis laser time when HoLEP were done with Moses 2.0 compared to a standard mode. Postoperative functional outcomes as well as complications were comparable between groups at 3 months. Due to a better hemostasis observed with the use of Moses 2.0, the authors changed their practice and moved to a same day discharged surgery in 70% of cases of HoLEP performed with this new technology.
Thulium Fiber Laser
The TFL, which must not be confounded with the continuous wave Thulium:YAG laser, operates at a wavelength of 1940 nm in a continuous wave or pulsed mode with a front-firing laser fiber. Recently, the Super Pulse TFL was introduced on the market. At this wavelength, the water optical absorption coefficient is 120 cm−1 (four times higher compared to Ho:YAG laser), which is its maximum absorption peak.[9–11] The theorical consequence of this is that more energy from TFL is absorbed by cells, and consequently results in a better ablation. Thus, the tissue penetration depth is 0.2 mm. In vitro studies reported higher incision and coagulation depths in continuous wave mode in comparison to the pulsed one.[20–22] At the same power output, a pronounced carbonization was reported in continuous wave mode. According to these results, Super Pulse TFL is presumed to have lower coagulation properties than to the continuous wave one. The studies included in this review report results with the continuous wave TFL only. Currently, no clinical study evaluated the new Super Pulse TFL.
Thulium fiber laser enucleation (ThuFLEP) was first described in 2018 in a retrospective study comparing three enucleation techniques: HoLEP, ThuFLEP, and monopolar enucleation of prostate (MEP). The authors reported that enucleation times were shorter with the laser techniques than MEP. Catheterization time and hospital stay were significantly shorter, and blood loss significantly lower, after laser enucleation techniques than MEP. For the three techniques, functional outcomes (IPSS, QoL, Qmax, and PVR) were comparable at 6 months. Except postoperative bleeding requiring prolonged bladder irrigation after MEP compared with laser enucleation techniques, complication rates were similar. This study concluded that ThuFLEP had similar outcomes than HoLEP and was an alternative to HoLEP. A randomized study focusing on learning curves of these three techniques found similar results.
In a prospective randomized study, Enikeev et al. compared ThuFLEP to monopolar TURP for the treatment of prostates < 80 mL. Operative time was significantly higher in the ThuFLEP group than the TURP one (46.6 ± 10.2 vs 39.9 ± 8.6 min). Catheterization time was significantly shorter after ThuFLEP than after TURP (1.4 vs 2.4 days). Hemoglobin decrease was significantly lower in the ThuFLEP group than in the TURP group (1.01 vs 1.8 g/dL). Both groups had comparable improvements in functional outcomes (IPSS, QoL, Qmax, and PVR) as well as complication rates at 12 months.
Since surgical treatment of men with prostates larger than 80 mL was classically limited to open prostatectomy, the same group compared in a retrospective study ThuFLEP with open prostatectomy for prostates larger than 80 mL. Catheterization time and hospital stay were significantly shorter, and blood loss and the need for blood transfusions significantly lower after ThuFLEP than the open prostatectomy. Functional outcomes (IPSS, QoL, Qmax, and PVR) were comparable.
The largest single-centre experience encompassing 1413 patients treated with HoLEP, ThuFLEP, or MEP within a time span of 5 years reported no significant different rates of complications intraoperatively, postoperatively, and at 6 months follow-up.
Since erectile function may be affected by BPH surgical treatment, Enikeev et al. compared in a retrospective study the postoperative changes between ThuFLEP and monopolar transurethral resection of prostate (TURP). The erectile function following ThuFLEP remained stable in 56%, improved in 26%, and impaired in 18% of patients. There was not de novo erectile dysfunction in patients treated by ThuFLEP. Erectile function following TURP remained stable in 43%, improved in 21%, and impaired in 36% of patients.
Many studies reported HoLEP as technically challenging with a steep learning curve. For this reason, a randomized study compared the learning curves with ThuFLEP, HoLEP, and MEP associated to a mentorship for the treatment of patients with prostate volume < 80 mL. The authors found that ThuFLEP tended to be associated with a shorter learning curve than HoLEP and MEP.
Blue Diode Laser
The diode lasers are semiconductor lasers. Currently, there are different diode lasers, operating in a continuous mode at different wavelengths. The blue diode laser operates at a wavelength of 450 nm at which the energy of the laser is strongly absorbed by hemoglobin, melanin, but not by water. Indeed, blood has a maximum absorption spectrum at 430 nm. Hemoglobin optical absorption coefficients at 532 nm green spectrum and at 450 nm blue spectrum are similar, in a range about 200 cm−1. Moreover, blue light tissue penetration depth is lower than infrared lasers. Thus, blue diode laser could be an alternative for green laser in soft tissue ablation and coagulation. First described in 2015 in dental surgery to reduce bacterial colonization, to coagulate, and cut soft tissue, this laser was a low power one (2W).[32,33] Currently, there is no clinical study evaluating the blue diode laser in Urology. Only in vitro studies investigating the laser-tissue interactions of blue diode laser were published.[22,34,35] Jiang et al. evaluated the effect of a 30W blue diode laser on bladder tissue vaporization and coagulation through incisions.[34,35] They reported, at 1 mm working distance with a 760 μm laser fiber, incision depths and widths of 1.67 mm and 1.62 mm at 1.0 mm/s of laser fiber displacement, and 1.89 mm, 2.37 mm, at 1.5 mm/s. The coagulation depth was about 460 ± 70 μm in contact mode. The authors found a higher incision depth with this new laser compared with a 532 nm green spectrum laser, but a thinner coagulation layer. Another in vitro study by Taratkin et al., with a comparable design than Jiang et al., compared a 60W blue diode laser with Ho:YAG laser, continuous wave TFL, and Super Pulse TFL. They found an incision depth of 0.7 ± 0.1 mm with a coagulation depth of 0.3 ± 0.1 mm, at 1 mm working distance with a 600 μm laser fiber and a 2.0 mm/s speed of laser fiber displacement. These results showed that incision depth with blue diode laser was intermediate between the Ho:YAG laser (higher values) and Super Pulse TFL (lower values), whereas coagulation depth was minimal with blue diode laser compared with these two other lasers. Evidence on blue diode laser remains limited, and further studies are needed.
The hybrid laser combines two lasers with different wavelengths: one has its maximum absorption in water and the other one has its maximum absorption with hemoglobin. Currently, this hybrid laser is still a prototype, and combines a continuous wave TFL (1940 nm) to a blue diode laser (450 nm). The objective of such laser is to combine the cutting abilities of the TFL and the coagulation properties of the blue diode laser. Indeed, laser energy is absorbed by the tissue via its relevant chromophores, which in the prostate are water and hemoglobin. In an in vitro study, Becker et al. compared this laser to a Ho:YAG laser and a continuous wave TFL on laser-tissue interactions through incisions on fresh nonfrozen porcine kidney samples. They reported that the hybrid laser had the deepest incision depth among the lasers tested with 7.3 ± 0.1 mm at 2 mm/s of laser fiber displacement. The coagulation zone was smaller compared to the other lasers. Microscopic analysis showed deep and narrow incisions with sharp margins with minimal carbonization. Similarly to the blue diode laser, evidence remains limited, and further studies are needed.
Curr Opin Urol. 2022;32(4):438-442. © 2022 Wolters Kluwer Health, Inc.