GreenLight Laser vs Diode Laser Vaporization of the Prostate: 3-Year Results of a Prospective Nonrandomized Study

Abstract

Background and Objective:

Laser vaporization of the prostate is one of the alternatives to transurethral resection of the prostate. Short-term studies report a comparable outcome after laser vaporization with the 532 nm 120-W GreenLight high-performance system (HPS) laser and the 980 nm 200 W high-intensity diode (diode) laser. In this study, we analyzed the intermediate-term results of both techniques.

Materials and Methods:

From January 2007 to January 2008, 112 consecutive patients with symptomatic benign prostate enlargement were nonrandomly assigned to treatment with the GreenLight laser or the diode laser. Perioperative parameters, postoperative functional outcome, complications, and the reoperation rate at 3 years were analyzed.

Results:

Improvement of voiding symptoms (International Prostate Symptom Score, quality-of-life) and micturition parameters (maximum flow rate, postvoid residual volume) showed no significant difference between the HPS group and the diode group. A significantly higher reoperation rate was observed in the diode group in comparison to the HPS group (37.5% vs 8.9%, p=0.0003) due to obstructive necrotic tissue (16.1% vs 0%, p=0.0018), bladder neck stricture (16.1% vs 1.8%, p=0.008), and persisting or recurrent adenoma (5.4% vs 7.1%, p=0.70), respectively.

Conclusions:

Both lasers lead to comparable improvement of voiding parameters and micturition symptoms. Treatment with the 200 W diode laser led to a significantly higher reoperation rate, which might be attributed to a higher degree of coagulation necrosis. Thus, a careful clinical application of this diode laser type is warranted.

Introduction

Laser treatment of the prostate has emerged as an alternative to transurethral resection of the prostate (TURP). Compelling scientific evidence could be acquired for the clinical application of Holmium laser enucleation of the Prostate (HoLEP) and photoselective vaporization of the prostate (PVP) with the 532 nm GreenLight laser.^1
–3 The latest guidelines of the European Association of Urology recommend HoLEP and PVP as minimally invasive treatment alternatives to TURP.⁴

Enhanced by the promising clinical efficacy and the economic success of PVP, other types of lasers for prostate vaporization, including diode lasers, emerged. Various diode lasers with different wavelengths and power output are currently available for application in prostate vaporization. However, there are distinct differences between laser types, which may be related to wavelength of the laser and the resulting laser–tissue interaction.^1,3 Randomized and large nonrandomized trials demonstrated the safety and efficacy of PVP with the 532 nm GreenLight laser.^1,5,6 However, only limited data with a maximum follow-up of 12 months are currently available for the 980 nm high-intensity diode laser.^7

–10

The aim of the current study is to present 3-year results of a prospective nonrandomized study comparing laser vaporization of the prostate with the 532 nm 120-W high-performance system (HPS) GreenLight laser and 980 nm 200-W high-intensity diode laser (diode). Based on our previously published short-term results with the 200-W diode laser,⁸ we hypothesized that the application of the diode laser may result in a higher rate of reoperations during intermediate-term follow-up.

Materials and Methods

Study population

Between January 2007 and January 2008, 112 patients with symptomatic benign prostate enlargement were assigned to treatment with the 120-W HPS laser or the 200-W diode laser. Group assignment was up to the operating surgeon's discretion. Preoperatively, patients underwent a standard evaluation, including digital rectal examination, urine analysis, transrectal ultrasound measurement of the prostate (TRUS), ultrasound evaluation of upper urinary tract, and determination of prostate-specific antigen (PSA) value. Before surgery, patients completed the International Prostate Symptom Score and quality-of-life questionnaire (IPSS-QoL). TRUS-guided prostate biopsies were performed before surgery in case of suspicious digital rectal examination or elevated PSA level. Patients with confirmed prostate cancer or previous transurethral surgery were excluded from the study. Furthermore, patients with known neurogenic bladder disease or neurologic disorders or a known history of spinal cord injury were excluded. The use of anticoagulants or platelet aggregation inhibition and indwelling transurethral or suprapubic catheter was not a criterion for study exclusion. There were no age limitations for study inclusion. Preoperatively, all patients provided informed consent for surgery. The local ethics committee approved the study as well as data analysis. Data storage was performed in consistence with good clinical practice guidelines.

Surgical technique

Both techniques were performed with a free-beam side-firing technique as described previously.⁸

Follow-up

Patients were followed up at 6 weeks and 3, 6, and 12 months postoperatively and yearly thereafter. At every follow-up, a standard evaluation was performed, including urine analysis, determination of the PSA value, measurement of maximal flow rate (Q _max), and postvoid residual volume (PVR volume). Furthermore, patients were asked to fill out the IPSS-QoL questionnaire.

Statistical analysis

All data presented are given as mean±standard deviation. Statistical analysis was performed using the SPSS 19.0 statistical software package (SPSS, Inc., Chicago, IL). The t-test was applied to compare two groups of independent parametric numerical data; the Mann–Whitney U-test was applied to compare the two groups of independent nonparametric numerical data. The Wilcoxon test was used for statistical analysis of changes during follow-up within the groups. The chi-square test was applied to compare categorical data (complications). A two-sided p-value of <0.05 was considered statistically significant.

Results

Preoperative characteristics

Preoperative characteristics are shown in Table 1. Patients matched in age, prostate volume, preoperative PSA, and rate of patients under platelet aggregation inhibition or oral anticoagulation. The rate of patients with indwelling preoperative catheter was higher in the HPS group (39.3% vs 24.6%, p=0.32).

Table 1.

Preoperative Patient Characteristics

Parameter	120-W HPS mean±SD (range) n=56	200-W diode mean±SD (range) n=56	p-Value
Age (years)	72±10 (51–96)	72±9 (55–88)	0.97
Prostate volume (mL)	69±49 (20–250)	65±30 (20–150)	0.55
PSA (μg/L)	5.4±7.4 (0.4–29.0)	4.3±4.7 (0.2–26.8)	0.46
IPSS	21±7 (9–30)	19±8 (5–34)	0.26
QoL	4±2 (0–6)	3±2 (0–6)	0.29
Q _max (mL/seconds)	11.7±5.5 (3.6–21.0)	10.7±5.4 (3.5–28)	0.56
PVR volume (mL)	172±145 (0–500)	179±304 (0–1500)	0.89
ASS (%)	17.8	19.6	0.81
Clopidogrel (%)	3.6	3	0.62
Oral anticoagulation (%)	17.9	14	0.36
Indwelling catheter (%)	39.3	24.6	0.32

ASS=aspirin; HPS=high-performance system; IPSS=International Prostate Symptom Score; PSA=prostate-specific antigen; PVR volume=postvoid residual volume; QoL=quality-of-life; SD=standard deviation.

Intra- and perioperative parameters

Details on intra- and perioperative parameters are shown in Table 2. Operation time and lasing time were comparable. Energy application per case was significantly higher with the diode laser (305±136 kJ vs 195±133 kJ, p<0.0001). Furthermore, the amount of energy per preoperative estimated prostate volume was significantly higher in the group of patients treated with the diode laser (5.3±1.8 kJ/mL vs 3.1±1.2 kJ/mL, p<0.0001). Catheterization time was significantly shorter after treatment with the diode laser (2.3±1.0 days vs 1.8±1.2 days, p=0.02); hospitalization time remained comparable between both the groups (5.7±2.6 days vs 6.5±8.2 days, p=0.52).

Table 2.

Intra- and Perioperative Values

Parameter	120-W HPS mean±SD (range) n=56	200-W diode mean±SD (range) n=56	p-Value
Operation time (minutes)	63±36 (20–180)	56±20 (20–105)	0.23
Lasing time (mL)	34±24 (4–120)	39±16 (11–89)	0.23
Energy per case (kJ)	195±133 (18–653)	305±136 (92–757)	<0.0001
Energy per preoperative prostate volume (kJ/mL)	3.1±1.2 (0.5–5.4)	5.3±1.8 (1.2–10.6)	<0.0001
Catheterization time (days)	2.3±1.0 (1–7)	1.8±1.2 (1–9)	0.02
Hospitalization time (days)	5.7±2.6 (3–22)	6.5±8.2 (2–64)	0.52

Functional outcome

During the postoperative course of 36 months, the voiding parameter and micturition symptoms improved in both groups. No significant difference in improvement of IPSS (p=0.16), QoL (p=0.76), maximum flow rate (p=0.95), PVR volume (p=0.30), and PSA value reduction (p=0.73) could be detected between both the groups (Table 3).

Table 3.

Functional Outcome

	120-W HPS preoperative mean±SD n=56	120-W HPS 36 months mean±SD n=21	200-W diode preoperative mean±SD n=56	200-W diode 36 months mean±SD n=26	p-Value improvement HPS v diode
IPSS	21±7	7±6	19±8	10±9	0.16
QoL	4±2	1±1	3±2	2±2	0.76
Maximum flow rate (mL/seconds)	11.7±5.4	18.0±10.3	10.7±5.3	16.4±8.8	0.95
Postvoid residual volume (mL)	157±133	28±47	179±300	19±46	0.30
PSA-value (μg/L)	5.4±7.3	2.5±2.2	4.3±4.7	2.5±3.9	0.73

Complications

Table 4 shows details on perioperative complications. Impaired visibility due to intraoperative bleeding was more frequently in the HPS group (14.3% vs 0%, p=0.003). No perioperative blood transfusion or transurethral resection syndrome was observed in either group. The rate of early postoperative storage symptoms was comparable between both groups (33.3% vs 36.1%, p=0.81), whereas a persisting dysuria at the 36 month follow-up was only reported in patients after treatment with the diode laser (none vs 19.2%; p=0.03). The reoperation rate at the 36-month follow-up was significantly higher after treatment with the diode laser (8.9% vs 37.5%, p<0.001) (Table 5). The higher reoperation rate with the diode laser was due to a significantly higher rate of sloughing caused by obstructive necrotic prostatic tissue (0% vs 16.1%, p=0.002) as well as symptomatic bladder neck strictures (1.8% vs 16.1%, p=0.008).

Table 4.

Perioperative Complications

Parameter	120-W HPS No. (%) n=56	200-W diode No. (%) n=56	Clavien–Dindo classification grade	p-Value
Impaired visibility due to bleeding	8 (14.3)	0 (0)	—	0.0033
Transfusions	0 (0)	0 (0)	II	—
TUR-syndrome	0 (0)	0 (0)	—	—
Change to TURP for coagulation or resection	4 (7.1)	2 (3.6)	—	0.40
Retention during hospitalization	5 (8.9)	11 (19.6)	IIIa	0.10

TUR syndrome=transurethral resection syndrome; TURP=transurethral resection of the prostate.

Table 5.

Postoperative (≤3 Years) Complications

Parameter	120-W HPS No. (%)	200-W diode No. (%)	Clavien–Dindo classification grade	p-Value
Dysuria (<6 weeks)	11/33 (33.3)	13/36 (36.1)	II	0.81
Dysuria (3 years)	0/21 (0)	5/26 (19.2)	II	0.03
Reoperation (total)	5/56 (8.9)	21/56 (37.5)	IIIb	<0.001
Obstructive necrotic tissue	0/56 (0)	9/56 (16.1)	IIIb	0.002
Persisting/recurrent adenoma	4/56 (7.1)	3/56 (5.4)	IIIb	0.70
Bladder neck stricture	1/56 (1.8)	9/56 (16.1)	IIIb	0.008

Discussion

TURP is regarded as the reference technique for the treatment of symptomatic prostate enlargement for prostates with a volume of 30–80 mL.⁴ Despite its proven efficacy, TURP can be associated with severe complications like bleeding or blood transfusion.¹¹ To overcome the limitations of TURP, several minimally invasive alternative treatments were developed in recent years.^3,12 Ablative laser techniques, which involve vaporization of prostate tissue, play an important role as alternatives to TURP.¹ Since the first report of effective laser vaporization of the prostate with a 532 nm high-power potassium-titanyl-phosphate laser in 1998, PVP has gained wide acceptance in the urologic community.¹³ In the last decade, the technique underwent modifications of fiber design and the maximum power output of the generator was increased to 120 and 180 W, respectively.

In contrast, various types of diode lasers with different wavelengths and maximum power output are available for prostate vaporization. When discussing the application of diode lasers in prostate vaporization, it is crucial to recognize that the wavelength of the laser directly affects the tissue–laser interaction. At 980 nm, the absorption of the laser energy is high in water and in hemoglobin. Thus, it is postulated that the 980 nm diode laser combines a high tissue ablation capacity with good hemostatic properties.

In our series, both lasers lead to a comparable improvement of voiding symptoms (IPSS, QoL), micturition parameters (maximum urine flow, postvoid PVR volume), and reduction of the PSA value at the 36-month follow-up. The improvement of these parameters in the HPS group was comparable to the 36-month results from the PVP arm of a prospective nonrandomized trial and a case series of 550 patients who underwent PVP with the 120-W laser.^14,15 While symptomatic improvement is highly relevant in the treatment of lower urinary tract symptoms, the reoperation rate is specifically important when reporting longer follow-up periods.

We observed a significantly higher reoperation rate after treatment with the diode laser compared to PVP. The reoperation rate of 8.9% after PVP in our series is in the range of the reported retreatment rate at 36 months in the literature, which ranges from 0% to 18.4%.^14
–16 The reoperation rate after diode laser vaporization can mainly be attributed to a high rate of obstructive necrotic tissue and bladder neck strictures.

A higher reoperation rate of the diode laser in comparison to 120-W HPS was also observed by Chiang et al.⁹ who report a 1-year reoperation rate of 9.1% and necrotic tissue in 18.2% of the cases. The high rate of obstructive necrotic tissue in our series, which primarily appeared within the first 6 months after treatment, suggests deep tissue coagulation necrosis with the diode laser. This is supported by an observed depth of tissue necrosis of 4.18±0.41 mm for the diode laser in comparison to 0.84±0.07 mm for the 120-W HPS laser in an ex vivo blood-perfused kidney model.¹⁷ This stands in contrast to experimental data on the same model, where an average coagulation zone of 0.29±0.05 mm with a 980 nm diode laser was observed.¹⁸ Different models of 980 nm diode lasers with different maximum power output could explain the discrepancies in the observed depths of coagulation. It is important to notice that a maximum power output of 200 W was used in the study with deeper coagulation, whereas a setting of 120 W was chosen in the study with the smaller coagulation zone. Seitz et al. observed deeper tissue coagulation with increasing power output of the 980 nm diode laser in experiments on human cadaver prostates.¹⁹ Deep tissue coagulation could be confirmed by experiments in living canines with increased maximum power output near the infrared wavelength spectrum. The application of a 980 nm 150 W diode laser for prostate vaporization resulted in a necrotic zone of 6.1±1.2 mm and was associated with prostatic obstruction by necrotic tissue in six of eight dogs.²⁰ In contrast, the 120 W HPS laser showed a coagulation zone of 1.5±0.3 mm in equally performed canine experiments.²¹

Although the 980 nm diode laser is not identical to the one used in the canine experiments, the results of these in vivo experiments corroborate the assumption that the high rate of obstructive necrotic tissue is related to the wavelength of the laser. Furthermore, the high incidence of bladder neck strictures in our series appears to be associated with increased scarring of the bladder neck due to coagulation necrosis.

In contrast, a lower reoperation rate after the clinical application of a 980 nm diode laser in other patient series suggests that wavelength of the laser is not the only parameter, which potentially could be held responsible for the unfavorable results, observed in our series. In 47 patients treated with a 980 nm diode laser with a maximum power output of 132 W, recatheterization was necessary in two patients and late bleeding after 4 weeks in one patient during a follow-up of 6 months but no reoperation.²² No reintervention was necessary within the first 6 months after treatment of 96 patients with a 980 nm diode laser at 120 W maximum power output.²³ These clinical data suggest that the use of a lower power setting at diode laser vaporization of the prostate appears to lead to superior clinical outcomes. A higher amount of total energy per case used in our series (305±136 kJ) compared to published series with favorable outcomes (243±93 kJ; 126±84 kJ) supports this assumption.^20,21 This means that at a maximum power setting of 200 W, which was used in the majority of our cases, the better part of the applied energy was used for deep tissue coagulation instead of superficial tissue vaporization. A lower zone of coagulation necrosis at lower power setting in vitro clearly supports this hypothesis.¹⁹

In an effort to reduce the incidence of postoperative necrotic tissue secondary to deep coagulation, a novel type of diode laser fiber with a quartz head was introduced recently. In contrast to the fiber used in our study, the quartz concentrates the energy at the tip of the fiber, which does not emit a free beam and thus works in contact mode.²⁴ In a prospective randomized study comparing 980 nm diode laser vaporization between side fire and quartz head fiber in 113 patients, the rate of significant tissue remnants and prolonged dysuria was significantly higher in the side fire group.²⁴ These results support the assumption that in noncontact mode, the wavelength of 980 nm is associated with deep tissue penetration. However, the promising results of the quartz head fiber warrant further confirmation with a longer follow-up.

We are aware of the limitations of our study. First, it was performed in a nonrandomized manner, which may lead to a selection bias in patient allocation. Second, we experienced a relatively high rate of patients lost to follow-up. Nevertheless, we are convinced that the results of our study, which to our knowledge represent the longest available follow-up after diode laser vaporization, provide useful information on the capability and limitations of the application of laser vaporization in the treatment of symptomatic benign prostate enlargement.

Conclusions

Both laser devices lead to a comparable symptomatic improvement. The diode laser is characterized by a higher reoperation rate due to obstructive necrotic tissue and bladder neck sclerosis indicating deep tissue necrosis. Based on our clinical experience, modifications of this 980 nm diode laser are necessary to reduce deep tissue necrosis resulting in postoperative complications.

Footnotes

Disclosure Statement

A.B. is consultant for the American Medical Systems (AMS) and Principal Investigator of a study comparing Photoselective Vaporization of the Prostate with the GreenLight XPS™ laser system and transurethral resection of the prostate for the treatment of benign prostatic hyperplasia (The Goliath Study). H.P. is a study nurse and partly paid by AMS. For the remaining authors, no competing financial interests exist.

Abbreviations Used

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