More efficient vaporization by the 200-W Thulium laser system than by the GreenLight high-performance system (HPS) 120-W system

by the system GreenLight Abstract Aim: We retrospectively compared and evaluated the postoperative complications in the ThuVAP group than in the HPS-PVP group (13.9% vs. 23.6%, P = 0.030). Conclusion: Both procedures are safe and useful for BPH obstruction. Based on shorter operating and hospitalization times, fewer complications, and more efficient tissue removal, ThuVAP is a more favorable and effective treatment than HPS-PVP.


INTRODUCTION
Transurethral resection of the prostate (TURP) is still the gold standard surgical treatment for benign prostatic hyperplasia (BPH). However, it is associated with a number of perioperative complications, including bleeding requiring transfusion, hyponatremia, and long-term indwelling urethral catheterization. Furthermore, this procedure requires the operator to be skilled, and its outcomes are dependent on the skill of the operator.
Laser vaporization for BPH, as typified by photoselective vaporization of the prostate (PVP), was initially performed in the 1980s to overcome the complications associated with TURP and is now conducted worldwide. Previous studies demonstrated that laser vaporization, particularly GreenLight laser vaporization, of the prostate was as safe and as efficient as TURP [1,2] .
A high-powered Thulium laser was initially introduced for the treatment of BPH in 2005 [3] . Since the thulium laser is strongly absorbed by water (abundant in all tissues), its cutting and vaporization speeds remain relatively constant during procedures regardless of tissue vascularization. Furthermore, its wavelength achieves an extremely low penetration (0.1-0.2 mm), efficient tissue ablation, and effective hemostasis [4] . Several techniques using the Thulium laser have been described for laser prostatectomy, including Thulium vapoenucleation, Thulium laser resection of the prostate (the 'tangerine' technique), and Thulium laser enucleation [5][6][7] . Although the Thulium laser is well suited for vaporization, the safety and efficacy of 200-W Thulium laser vaporization of the prostate (ThuVAP) have only recently been reported [8] . Therefore, we herein compared the efficacy and safety of ThuVAP and GreenLight 120-W highperformance system (HPS) photoselective vaporization of the prostate (HPS-PVP).

METHODS
In this single institutional retrospective study, we collected data on 137 men who underwent ThuVAP ( 200-W Cyber TM) for BPH between February 2019 and December 2021 and 233 men who underwent HPS-PVP between October 2014 and April 2019. Twenty-two out of 137 patients in the ThuVAP group and 54 out of 233 in the HPS-PVP group received anticoagulant therapy, and all underwent surgery without the cessation of this treatment.
We utilized a Storz 23Fr laser resectoscope. Both procedures were initiated under general anesthesia, and a cavity similar to that of TURP was formed in the prostatic urethra. Hemostasis was confirmed with an emptied bladder and the removal of any tissue pieces or clots. The bladder was then re-filled, an 18F 2-way catheter was gently introduced, and its balloon was inflated with 20 cc of saline.
Prostate-specific antigen (PSA) levels, International Prostate Symptom Scores (IPSS), quality of life (QOL) scores, overactive bladder symptom scores (OABSS), post-void residual (PVR), maximum flow rates (Qmax), and prostate volumes (PV) were assessed in all patients before surgery. Eighty-two out of 137 patients in the ThuVAP group and 198 out of 233 in the HPS-PVP group underwent a pressure flow study (PFS) before surgery. Patients were followed up 1, 3, 6, and 12 months after surgery.
Complications were prospectively described in the present study and included OABS, stress urinary incontinence, dysuria, urinary tract infection, urinary retention, hematuria, and urethral stricture. Complications were categorized according to the Clavien-Dindo classification [9] .
All data are shown as the mean ± standard deviation. The Mann-Whitney U test was performed to analyze the significance of differences. Significance was defined as a P value < 0.05. All statistical analyses were performed using EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), which is a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria). More precisely, it is a modified version of R commander designed to add statistical functions frequently used in biostatistics.
Twenty-two patients were receiving anticoagulant therapy at the time of surgery in the ThuVAP group, and no significant differences were observed in the length of the catheter time, length of the hospital stay, or decreases in serum hemoglobin levels between those treated with or without anticoagulants. In contrast, 54 patients were receiving anticoagulant therapy at the time of surgery in the HPS-PVP group, and a significant difference was noted in the length of the catheter time between those treated with or without anticoagulants (39.9 and 30.9 h, P = 0.001) [ Table 4].   Functional outcomes were reported before and 1, 3, 6, and 12 months after surgery [ Table 5]. In the ThuVAP group, the mean values for IPSS, QOL, OABSS, Qmax, and PVR were 23.2, 5.4, 7.0, 6.9 mL/s, and 107.0 mL, respectively, before surgery and 4.1, 1.2, 2.4, 22.5 mL/s, and 6.6 mL, respectively, 1 year after  surgery. In the HPS-PVP group, the mean values for IPSS, QOL, OABSS, Qmax, and PVR were 22.1, 5.1, 6.3, 7.6 mL/s, and 102.1 mL, respectively, before surgery and 4.7, 1.3, 2.4, 17.6 mL/s, and 8.0 mL, respectively, 1 year after surgery. All functional outcomes significantly improved from baseline and appeared to be maintained during the follow-up period. Mean changes in PSA levels from baseline were 3.6 and 2.9 in the ThuVAP and HPS-PVP groups, respectively.
Complications categorized according to the Clavien-Dindo classification are listed in Table 6. Two (1.5%) patients in the ThuVAP group and nine (3.9%) in the HPS-PVP group were treated for stress urinary incontinence 1 month after surgery. Furthermore, two (1.5%) patients in the ThuVAP group and 19 (8.2%) in the HPS-PVP group had urinary retention 1 month after surgery, which required treatment with urinary catheterization for a few days. In addition, hematuria was detected in three (2.2%) and one (0.9%) patients in the ThuVAP group 1 and 3 months after surgery, respectively, and in seven (3.0%) and one (0.4%) in the HPS-PVP group 1 and 12 months after surgery, respectively, which required treatment with a hemostatic agent. Regarding bladder pain, three (2.2%) patients in the ThuVAP group developed pelvic pain that was exacerbated by bladder filling 1 month after surgery. Two patients in the ThuVAP group and seven in the HPS-PVP group had a confirmed diagnosis of bladder neck contracture by cystoscopy within 6 and 12 months of surgery, respectively, which required transurethral incision. Nineteen patients (13.9%) in the ThuVAP group and 55 (23.6%) in the HPS-PVP group (P = 0.030) developed at least one complication.
In the ThuVAP group, a multivariate analysis of risk factors for postoperative complications identified preoperative balloon catheter placement as a significant risk factor (OR: 8.270, P = 0.012) [ Table 7]. Conversely, no significant risk factors for postoperative complications were identified in the HPS-PVP group by univariate or multivariate analysis.

DISCUSSION
The Thulium laser (2013 nm) is strongly absorbed by water and may be operated in a continuous wave; therefore, a coagulated layer easily forms in tissue and the hemostatic power of the laser is high. Since the Thulium laser is a direct-injected fiber, it may be used for a number of purposes, such as enucleation, resection, and vaporization [10] . Furthermore, it is reusable and has a high energy limit; therefore, it is costefficient and effective for large BPH. In recent years, there have been a number of conference presentations on the use of the 200-W high-powered Thulium laser for ThuVAP.
ThuVAP is associated with a low risk of bleeding and its safety has been demonstrated; therefore, it may be performed on very elderly and high-risk patients receiving anticoagulant therapy. Although the Thulium laser is commonly used for vapoenucleation or resection of the prostate, limited information is currently available on ThuVAP. In vapoenucleation or resection of the prostate using the Thulium laser, 0.6%-7.1% of patients required perioperative blood transfusions. However, it remains unknown whether a perioperative blood transfusion is needed for ThuVAP [5,6,11] .
In 2014, Pariser et al. reported the short-term outcomes of 150-W (CyberTM) thulium laser vaporization of the prostate (150-W ThuVP) over a period of 3 months [8] . Fifty-nine patients with a mean PV of 57 ± 30.2 mL underwent 150-W ThuVP; 47% were receiving anticoagulants. The majority (78%) of patients were discharged on the same day of surgery. Although a significant change was observed in hemoglobin levels from baseline (13.1-12.4 g/dL), no patients received blood transfusions.
In comparison with HPS-PVP, the present results demonstrated the safety of ThuVAP. Mean PV in the ThuVAP group was 77 ± 36.6 mL and 16% of patients were receiving anticoagulants. Average postoperative catheterization and hospitalization times were 34.2 h and 4.9 days, respectively, and no significant differences were observed in these times between patients treated with and without anticoagulants. Although a significant change was noted in hemoglobin levels from baseline (14.2-13.5 g/dL, P < 0.001) in the present study, no patients received blood transfusions and no significant differences were detected in  this decrease between patients treated with and without anticoagulants.
Vargas et al. reported the outcomes of 150-W ThuVP in 52 patients without anticoagulants (mean PV of 42.5 ± 17.4 mL) in a 6-month follow-up [12] . Significant improvements were observed in mean IPSS (reduction of 17 points) and Qmax (mean improvement of 9.33 mL/s). In the present study, preoperative IPSS was 23.2 points, with 21% of patients exhibiting urinary retention at the time of surgery. A marked reduction was noted in IPSS 1 month after surgery (mean 8.3 points), and it continued to gradually decrease until 12 months (mean 4.1 points). This result suggests immediate improvements in obstructive urinary symptoms, whereas the attenuation of bladder storage symptoms was slower. IPSS was 82.3% (19.1 points) in the 12-month follow-up, which was lower than the baseline. Regarding urodynamic parameters, improvements were observed in mean Qmax (6.9-22.5 mL/s) and PVR (107.0-6.6 mL) from preoperative parameters. Although the average PV (77.0 ± 36.6 mL) in the present study was significantly larger than those in two previous 150-W ThuVP studies, the results obtained were similar. We suggest that an improved Thulium laser output (previous studies: 150-W, our study: 200-W) resulted in similar surgical outcomes for large BPH.
A reduction in PSA levels is associated with the holmium laser enucleation of the prostate as a surrogate marker for BPH adenoma removal, and is a useful parameter for evaluating the success of other BPH obstruction surgeries. In the present study, mean PSA levels decreased to 3.6 and 2.9 ng/mL from baseline after three months in the ThuVAP and HPS-PVP groups, respectively. ΔPV were 50.4 and 27.8 mL (P < 0.001) in the ThuVAP and HPS-PVP groups, respectively, while mean ΔPV/laser times (vaporization efficiency) (mL/min) were 1.1 and 0.5 (P < 0.001), respectively. Hueber et al. reported that HPS-PVP retreatment rates were significantly higher for prostates > 100 cc [13] . Due to the limited energy use of the fiber in HPS-PVP, which may only be used once, this procedure may increase the reoperation rate during the long course of residual adenoma in large BPH. In contrast, 200-W ThuVAP is characterized by a high fiber output and increased energy availability, the vaporization efficiency of which is more than 2-fold higher than that of the GreenLight HPS 120-W system and allows for the sufficient vaporization of large BPH.
In the present study, overall complication rates were 13.9 and 23.6% (P = 0.030), while major complication rates were 1.5 and 3.0% in the ThuVAP and HPS-PVP groups, respectively, and a multivariate analysis identified anticoagulant therapy and preoperative balloon catheter placement as risk factors for complications in the ThuVAP group. Although anticoagulant therapy was a risk factor in the ThuVAP group, no significant differences were observed in the length of the catheter time or hospital stay between those treated with or without anticoagulants. Preoperative balloon catheter placement has been identified as a risk factor for postoperative febrile urinary tract infections (fUTIs). We performed urine cultures before surgery and administered antibiotics to patients with a positive culture one day before surgery. Although preoperative balloon catheter placement is a risk factor for postoperative fUTIs, the present results will facilitate the prevention of postoperative fUTIs in the future.
In the present study, overall complication rates were significantly lower in the ThuVAP group than in the HPS-PVP group. This result may have initially been attributed to the introduction of the HPS-PVP system, and then to the ThuVAP system after we gained experience performing vaporization.
However, based on our experience of HPS-PVP and ThuVAP, we recognize that ThuVAP has contributed to marked improvements in vaporization efficiency while retaining the safety of previous vaporization systems, such as HPS-PVP. ThuVAP is a relatively new surgical procedure and since limited information is currently available on its outcomes, further studies are warranted.
The results obtained on 137 patients who underwent 200-W Cyber TM ThuVAP with a 1-year follow-up in the present study confirmed very few complications and improvements in IPSS, QOL scores, OABSS, Qmax, and PVR from 1 to 12 months after surgery. It is important to note that the ThuVAP group had significantly fewer postoperative complications than the HPS-PVP group and vaporization efficiency was more than two-fold higher.
There are some limitations that need to be addressed. The present study included a small sample size and had a short follow-up period. It was also a retrospective analysis of a prospectively maintained database of one institution. Despite these limitations, the present results support the safety, utility, and costeffectiveness of 200-W Cyber TM ThuVAP, which is beneficial not only for patients, but also for medical personnel.
In conclusion, HPS-PVP and ThuVAP are both safe and useful surgical procedures for patients with BPH. Based on shorter operating and hospitalization times, fewer complications, and more efficient tissue removal, ThuVAP is a more favorable and effective treatment than HPS-PVP. The 200-W Thulium laser is suitable for vaporization of the prostate, which may be completed by vaporization alone even if it is very large.

Authors' contributions
Conception and design of the study and performed: Shinohara M, Hirao Y Data analysis and interpretation: Shinohara M, Hirao Y, Fujimoto K, Saka T

Availability of data and materials
All data generated or analyzed during this study are included in this published article.

Financial support and sponsorship
None.

Conflicts of interest
All authors declare that there are no conflicts of interest.

Ethical approval and consent to participate
The present study was performed in accordance with the ethical principles of the Declaration of Helsinki. The protocol was approved by the Ethics Committee of Osaka Gyoumeikan Hospital (IRB approval number: 21-0017).