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BEST OF 2019: Edited by Johannes W. Vieweg and Shahrokh F. Shariat

The changing role of lasers in urologic surgery

Enikeev, Dmitrya; Shariat, Shahrokh F.a,b,c,d; Taratkin, Marka; Glybochko, Petra

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doi: 10.1097/MOU.0000000000000695
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Abstract

INTRODUCTION

Lasers were introduced into urology over five decades [1]. However, their rapid development only began in the end of the 1990s [2]. Nowadays, lasers have become an integral part of urologic surgery, often allowing for safer interventions in patients with comorbidities, more efficient conventional treatments, and even shorter learning curves. Better awareness of laser effects and efficacy contributed to increased interest in and wide adoption of different lasers. A search for more effective approaches has continuously stimulated researchers and medical companies to research on new improved laser systems. These developments have, in turn, led to a growing number of indications and utilizations without least a two-fold increase in publications on laser surgery in the medical literature during the last decade alone.

To explore new developments in the field of laser surgery, clarify their role and discuss developing techniques, we performed a review of the current literature via PubMed–MEDLINE, Web of Science, Scopus, and Google Scholar.

Box 1
Box 1:
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BENIGN PROSTATIC HYPERPLASIA

Lasers have repeatedly shown their efficacy in benign prostatic hyperplasia (BPH) surgery as their introduction in the 1980s [3]. Current techniques of laser surgery for BPH include ablation, vaporization, resection, and endoscopic enucleation (EEP). The latest, EEP, is often considered a preferred treatment for BPH of any size [4]. Multiple devices have been proposed for EEP. Despite comparable efficacy of different EEP techniques their safety, convenience for the surgeon and learning curve need to be evaluated [5].

Holmium laser enucleation (HoLEP) has been the most widely used treatment EEP option for decades. Despite its high efficacy, the technology keeps evolving aiming for better performance. A recent addition to the Ho: yttrium-aluminium garnet (YAG) system to enhance laser performance during lithotripsy, the so-called Moses technology (delivery of two laser pulses in a short period for maximum energy delivery), is likely to improve the efficacy of HoLEP as well. Kavoussi et al.[6▪] argue that EEP with Moses technology is at least similar to regular HoLEP, with potentially better vaporization, improved hemostasis, and faster tissue separation. The authors suggest that it could optimize the incision process making the procedure easier [6▪]. Meskawi et al.[7] reported their initial experience with Moses EEP in large glands (mean volume, 82 g); however, no functional outcomes were presented. Currently, there is no published data on this technique except conference articles; therefore, further studies are necessary to understand how Moses could improve HoLEP.

One of the most intriguing additions to surgical lasers is a thulium-fiber laser (TFL). The main features of TFL distinguishing it from Ho:YAG is its wavelength of 1.94 μm (leading to four-fold increase in water absorption and lesser penetration depth of 0.15 mm) (Table 1) and pulse shape. With identical average and peak powers of 100 W, the laser does not burst tissues, allowing for clean and precise cutting instead [8]. Conversely, Ho:YAG's average power is about 100 W and its presumable peak power is around 10–15 kW. With such an outburst of energy, each pulse of Ho:YAG creates a large vapor bubble which ruptures the tissue [9▪▪].

Table 1
Table 1:
Laser properties [53–55].

TFL's efficacy in BPH surgery has already been proven to match those of conventional HoLEP and monopolar electroenucleation (MEP). Surgery times, rates of postoperative complications and short-term outcomes were comparable between HoLEP and TFL enucleation of the prostate (ThuFLEP) [10]. It has also been shown that despite comparable outcomes, ThuFLEP may have a faster learning curve. During a trial on learning curves of MEP, HoLEP, and ThuFLEP, the authors found that ThuFLEP and HoLEP had significantly better enucleation rates than MEP (1.3 versus 0.9 versus 0.8 g/min; P = 0.011) and that ThuFLEP enucleation rate was even better than that of HoLEP [11▪]. Further comparative studies on functional outcomes of ThuFLEP versus transurethral resection of the prostate (TURP) showed that TFL allowed for slight improvement in International index of erectile function-5 score (+0.72), whereas TURP decreased it (−0.24) (P < 0.001) [12]. Another study revealed improved safety of ThuFLEP over open simple prostatectomy in large-sized glands with comparable functional outcomes [13]. Despite a small number of clinical studies on ThuFLEP, the available clinical data are consistent with previously published in-vitro findings [14,15]. Therefore, TFL is a promising new modality for BPH surgery that shares advantages with other endoscopic enucleation techniques and offers promising potential improvement.

The GreenLight laser previously proved safe for vaporization with good short-term outcomes and minimum complication rates. The recently developed technique of greenlight laser enucleation of the prostate (GreenLEP) was described by Gomez Sancha et al.[16] as a promising emerging modality for large-sized glands. In recent publications, GreenLEP performed better than HoLEP with a shorter learning curve [17]. However, no data on long-term outcomes of GreenLEP are present, and the available information is mostly from retrospective series.

Moreover, relevant data on GreenLEP should be evaluated in the context of the 1470-nm diode laser. This device with peaks of absorption in both water and hemoglobin matching those of GreenLight is used for vaporization and enucleation. Vaporization with the 1470-nm diode laser was explored by Liu et al.[18] and considered an effective option for benign prostatic obstruction relief with presumably better hemostatic properties than GreenLight; however, no data on difference in blood loss between the techniques were presented. Zheng et al. conducted a prospective trial on the efficacy and safety of diode laser enucleation of the prostate (DiLEP) (with a 1470 nm diode laser) and plasma-kinetic resection (PKRP) [19]. DiLEP was found to possess functional efficacy and safety similar to PKRP, yet allowed for shorter operation time (55 versus 95 min), quicker catheter removal, and decreased hospital stay [19]. Despite these results, the 1470-nm diode laser enucleation and vaporization require further well-designed prospective studies.

BLADDER CANCER

The current standard for nonmuscle invasive bladder cancer is transurethral resection of bladder tumor (TURBT) [20]. However, over a third of the patients who undergo TURBT will experience recurrence [21–23]. It has previously been confirmed that the absence of detrusor in the specimen is associated with an increased risk of relapse [24]. Detrusor in the gross sample was present in 50–86% of cases after TURBT leading to understaging [25]. Therefore, a more effective technique is needed. Lasers have been used for bladder cancer (BCa) surgery since their invention. However, treatment approaches underwent dramatic changes over time. Development of surgical techniques and emergence of new lasers (Ho:YAG and Tm:YAG) allowed shifting from vaporization to en-bloc resection of bladder tumor (ERBT) with subsequent studies demonstrating high efficacy and safety of the new technique [26]. Among the main advantages of laser ERBT is higher rate of detrusor detection (>95%) and better quality of the specimen for pathology compared with TURBT [13]. Kramer et al.[26,27] performed studies on electrical versus Ho:YAG versus Tm:YAG laser ERBT and found no significant differences in surgery duration, catheter stay, complication rate and recurrence after 1 year. Yet, Tm:YAG could be more favorable than Ho:YAG for en-bloc resection because of its continuous mode of firing. It allows for clearer cuts, yet with prominent carbonization [28].

Emerging modalities such as TFL are still locking significant information on their efficiency. Rapoport et al.[29] presented the first trial of TURBT versus TFL-ERBT describing better safety profile of TFL-ERBT (absence of obturator reflex) and higher rate of detrusor (58.6 versus 91.6%).

Despite growing popularity of en bloc, the search for easier and safer treatment modalities for BCa continues. Hermann et al. reported the first trial on outpatient diode laser (980 nm) vaporization with local anesthesia for recurrent BCa [30]. A total of 21 cases were described with only Clavien–Dindo I complications in 30% of patients and 24% of recurrences after 12–16 months of follow-up. Only one patient experienced significant pain (seven on the visual analog scale) [30]. The authors believe that such an approach may help cut treatment costs as they are more tolerable, with a specific benefit in the frail, multimorbid elderly clientel [30,31]. Further randomized controlled trials may shed more light on the topic.

LITHOTRIPSY

Since the end of the 1960s, when the first trial on stone fragmentation with ruby laser was published, interest in lasers as lithotripters has been growing constantly [32▪]. Further development in the field allowed shifting from continuous to pulsed lasers which improved lithotripsy. Currently, the most effective laser lithotripter is Ho:YAG laser, because of its high energy absorption in water and substantial peak power (∼10 kW). Holmium laser ablates stones in two steps. First, it creates a massive outburst of energy which instantly heats the stone and leads to its chemical decomposition. Second, stone fragments are blasted away with photomechanical power of Ho:YAG [9▪▪]. Currently, Ho:YAG yields even better results than pneumatic lithotripsy with significant reduction in surgery time (weighted mean difference = −11.52, 95% confidence interval (CI) −17.06 to −5.99, P < 0.0001) and better stone-free rates (odds ratio 2.12, 95% CI 1.40–3.21, P = 0.0004) [33].

The recently added Moses technology in the new generation of Ho:YAG lasers uses two separate pulses. The first is a short, low-energy pulse which creates a vapor bubble parting the water around the fiber tip, allowing the subsequent longer, higher energy pulse to deliver a larger amount of laser energy. Two key advantages of this approach are smaller bubbles (which decrease retropulsion) and better stone ablation [34]. Winship et al.[35] evaluated Ho:YAG with Moses technology in vitro and found it superior to conventional Ho:YAG lithotripsy in both short and a long-pulse settings. Elhilali et al.[36] in their study of Moses Ho:YAG versus regular Ho:YAG reported a better in-vitro ablation rate with at least two-fold increase in efficacy and lower retropulsion rates (P < 0.05); in-vivo safety profile rivaled that of conventional Ho:YAG. Mullerad et al. published the first clinical study on Moses technology [37]. However, because of the limited amount of participants (34 in total), they were unable to find any significant differences between regular Ho:YAG and Moses Ho:YAG. Ablation rates were 58.1 and 95.8, respectively (P = 0.19) [37]. Mekayten et al. retrospectively tested a low-powered 20 W Ho:YAG laser with Moses technology and found significant surgery time reduction of 234.91 s on multivariate regression analysis (P < 0.0001) [38]. However, such decrease may be easily attributed to high power of the laser and not to the Moses technology. Therefore, further randomized studies are necessary [38].

Another emerging technology is TFL which, with its better efficiency and lower retropulsion, may rival Ho:YAG. The water absorption coefficient for TFL (Table 1) allows for absorption of laser energy that is four times that of the Ho:YAG, which theoretically leads to more efficient stone ablation [39,40]. Andreeva et al. demonstrated that TFL allows for significantly higher in-vitro ablation rates for the majority of laser settings [41▪]. Surprisingly, greater energy absorption does not convert into higher temperature rise during the procedure [41▪]. TFL is able to reach a peak power of 500 W and because of the continuous nature of the pumping diode (which substitutes Ho:YAG's flashlamps), the laser is able to maintain the peak power throughout the duration of the pulse. The prolonged peak power of the TFL separates water and delivers a significant amount of energy to the stone, whereas lower peak power results in a smaller bubble and, subsequently, decreased retropulsion (about four times less) [34,41▪]. This could possibly compete with the Moses technology. In a first in-vitro comparative study of Moses Ho:YAG and TFL by Laurian et al.[42▪], the authors found that TFL allowed for almost three times better ablation.

To date, there are no published studies on TFL clinical efficacy except conference abstracts. Traxer et al. conducted a study on 268 patients who underwent TFL lithotripsy for kidney (N = 173; mean size: 11.4 mm; density: 330–1960 HU), ureter (N = 80; mean size: 7.6 mm; density: 460–1700 HU) or bladder (N = 15; mean size: 22.2 mm; density: 860–1050 HU) calculi. Lithotripsy was well tolerated and efficient in all patients [43▪]. Mean laser on time was 24.3, 12.7, and 14.5 min, respectively. With power settings of 0.5 J, retropulsion was insignificant [43▪]. Recent data suggests that TFL seems to be at least as effective as holmium laser. However, further research into its efficacy and safety is required.

LAPAROSCOPY

One of the first attempts at using lasers in laparoscopy was made by Barzilai et al.[44] with a CO2 laser back in 1982. Since then, different lasers have been proposed as possible laparoscopy tools (Ho:YAG, KTP:YAG, 980 and 1470 nm diode lasers, Tm:YAG). However, we still face the same barriers: any laser leads to significant smoke formation, pulsed lasers such as Ho:YAG may result in blood splashing and continuous-wave lasers usually lead to extensive carbonization [45]. Drerup et al.[46] recently confirmed these facts; in their study of diode laser efficacy they found that diode laser partial nephrectomy is feasible and allows for effective bleeding control, yet results in extensive carbonization. A promising technology for this surgery may be the newly developed blue diode laser (BDL) which, according to Jiang et al., is four times more effective than a 532-nm laser (ablation rates 5.14 and 1.20 μl/s, respectively); yet it still produces a carbonization layer [47]. A possible solution for this is hybrid technology presented by Taratkin et al. – a TFL–BDL hybrid which during an in-vitro study showed deeper incisions than Ho:YAG (3–7 times deeper), TFL or BDL alone (two times deeper) [48]. Also, the hybrid was capable of making carbonization-free incisions. However, studies exploring its potential are lacking [48].

PROSTATE CANCER ABLATION

One of the first in-vivo studies of focal laser ablation (FLA) in the prostate was published by Amin et al.[49] in 1993. Despite initially successful ablation of the lesion, it relapsed during the first year. This and further failures resulted in lack of further development of focal laser ablation because of problems with targeting and suboptimal temperature mapping. Nowadays, interest in FLA has been reignited with introduction of magnetic resonance-targeting and temperature control. Currently, one of the most popular systems is Visualase which uses an magnetic resonance targeting device and 980 nm low-power diode laser. Oto et al. reported phase I results in 11 clinically low-risk PCa patients with relapse-free survival (RFS) rate of 78%. In three patients, relapse (Gleason 6) was found on magnetic resonance-guided biopsy at six months [50]. Walser et al.[49] reported similar RFS rates 12 months after surgery – 83%. In contrast to these two reports, Natarajan et al.[52] only detected no disease in three of 11 patients six months after surgery (RFS, 27%). None of the authors found any decrease in urinary or sexual function [50,51▪,52]. This makes FLA a safe, yet not adequately tested technique. Further research is necessary to measure its oncological efficacy.

CONCLUSION

Lasers are an integral part of urology that is constantly evolving. The addition of Moses technology to Ho:YAG devices have substantially increased efficacy of lithotripsy, and possibly BPH treatment. Laser en-bloc resection of BCa seems efficient, yet more dependent on the technique itself rather than the device. Despite promising results achieved in some studies, current efficacy of laser systems for prostate cancer ablation remains unclear and further research is necessary. The use of lasers in laparoscopy is currently restricted because of smoke formation and carbonization; however, emerging technologies may solve this problem. The new generation of laser devices, thulium-fiber lasers, promise to become multipurpose tools, capable of shifting the standards of BPH and BCa treatment, as well as laparoscopy and lithotripsy.

Acknowledgements

None.

Financial support and sponsorship

None.

Conflicts of interest

There are no conflicts of interest.

REFERENCES AND RECOMMENDED READING

Papers of particular interest, published within the annual period of review, have been highlighted as:

  • ▪ of special interest
  • ▪▪ of outstanding interest

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Keywords:

bladder cancer; benign prostatic hyperplasia; laparoscopy; laser; lithotripsy; prostate cancer

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