Thulium Fiber Laser vs Pulse-Modulated Holmium MOSES Laser in Flexible Ureteroscopy for the Management of Kidney Stones: A Single-Center Retrospective Analysis

Abstract

Introduction and Objective:

The study's primary objective was to compare the laser efficiency and clinical outcomes of two widely used systems, the holmium MOSES laser and the thulium fiber laser (TFL), in managing kidney stones. The secondary outcomes were to evaluate the impact of stone composition on laser efficacy.

Methods:

We conducted a retrospective review of patients who underwent flexible ureteroscopy (f-URS) for solitary renal calculi between December 2020 and August 2022 at our institution and had a 3-month postoperative CT scan. Patient demographics and stone parameters were recorded, including stone site, size, volume, and density. Intraoperative data were collected and analyzed, including total operative time, ureteroscopy time, lasing time, technique, total energy delivered, and stone composition. All patients underwent a CT scan at 3 months follow-up. We recorded the presence of residual stones and the percentage of stone volume reduction. Ablation efficiency was calculated by dividing the energy utilized (J) by the stone volume (mm³). The ablation speed was calculated by dividing the stone volume (mm³) by the lasing time (seconds). Patients with a stone size <4 mm were deemed stone-free.

Results:

The MOSES and TFL groups comprised 62 and 49 patients, respectively. There were no significant differences between groups for baseline patient demographics or stone characteristics. The two modalities had comparable total energy, laser time, efficacy, and ablation speeds. No differences were detected in stone-free rates or complications between both groups. When dealing with calcium phosphate stones, we observed that the lasing time was significantly shorter with MOSES than TFL (7.95 vs 10.85 minutes, respectively [p = 0.01]).

Conclusions:

MOSES and TFL laser systems had comparable efficacy for lithotripsy of renal calculi during f-URS; however, calcium phosphate stones had a longer lasing time with TFL. REB Number: 100210.

Introduction

Urolithiasis is a highly prevalent illness affecting 1%–13% of the global population.¹ Flexible ureteroscopy (f-URS) coupled with laser lithotripsy has emerged as a popular treatment option owing to its minimal morbidity and excellent outcomes.^2,3 Two of the most common lasers, holmium and thulium fiber laser (TFL), are among the top available tools for urologists worldwide. When selecting a laser, urologists typically consider factors such as economic viability, versatility, and efficiency, all of which are critical for achieving optimal outcomes.

The holmium:yttrium–aluminum–garnet (Ho:YAG) laser has been a pioneer in laser application for urological procedures, particularly for URS lithotripsy, and has remained the gold standard for decades.^2,3 In recent years, the holmium laser urology platform has undergone several updates, including the introduction of a revolutionary pulse modulation technology called MOSES, followed by an updated version, MOSES 2.0. Pulse modulation involves the rapid emission of two consecutive pulses, where the first pulse creates a cavity in the water, enabling the second pulse to travel through the bubble and conserve energy. The latest update provides utilization of frequencies up to 120 Hz in addition to benefits offered by the first update, such as improved energy delivery to treat the stones with the option to select the energy delivery distance at the surgeon's discretion, reduced stone migration during the procedure, and minimal collateral tissue damage.^4
–6

Recent advances in laser fiber technology have led to the development of TFL. TFL utilizes thin silica fibers, which provide several benefits, such as enhanced endoscope performance owing to easier deflection and a larger working channel space. In addition, TFL's physical attributes, including its emission of pulsed infrared light at a wavelength of 1940 nm, which is close to the water absorption peak, enable high lithotripsy efficiency, production of smaller stone fragments, and better stone dusting capabilities than the standard Ho:YAG laser, even when adjusted to the same power settings.^{6

–15}

Previous studies comparing the efficacy of TFL with Ho:YAG laser demonstrated superior results for TFL during lithotripsy.^16

–20 However, other studies showed comparable outcomes between TFL and the holmium MOSES laser.^21,22 Our study's primary objective was to compare the clinical efficiency and outcome measures of two widely used systems, MOSES and TFL, in managing kidney stones. The secondary outcomes were to evaluate the impact of stone composition on laser efficacy.

Materials and Methods

After obtaining approval from the Research Ethics Board, we conducted a retrospective study on cases of solitary CT-confirmed renal stones that were managed with f-URS and laser lithotripsy using either a 60-W SOLTIVE™ SuperPulsed thulium fiber laser (Olympus) or a MOSES technology P120 H laser system (Lumenis^®Pulse) between December 2020 and August 2022. We excluded cases that involved a bilateral or staged procedure and patients in which ureteral stones were concomitantly present.

Preoperative CT scans were analyzed to determine stone characteristics, including stone site (upper pole, middle pole, lower pole, or renal pelvis), three-dimensional size (width [W], length [L], and height [H]), and stone density. Stone volume was calculated utilizing the ellipsoid formula (π × L × W × H × 0.167).²³ The presence of hydronephrosis (HN) and preoperative ureteral stents were also documented.

All patients underwent their procedures at the same hospital and were operated on by various surgeons, including attending physicians and fellows. Procedures were conducted using either a single-use or reusable ureteroscope, and the laser fiber size used was 200 μm for MOSES and TFL. Lasing time and laser energy were recorded by the laser systems, and the type of laser, laser settings, and lasing technique (fragmentation, dusting, or combined) were documented. Operative (OR) time was defined as the time from the cystoscope introduction for guidewire insertion to stent insertion, whereas the ureteroscopy time was measured from the insertion to the withdrawal of the ureteroscope. For cases involving the insertion of a ureteral access sheath, stenting was performed at the end of the procedure. Surgeons made sure to retrieve at least one calculus piece for chemical analysis.

Laser lithotripsy efficiency was quantified by measuring lasing time, laser energy, and stone volume. Ablation efficiency was described as the amount of energy required to fragment 1 cubic millimeter (mm³) of stone material and calculated by dividing laser energy per Joule (J) by the stone volume (J/mm³). Ablation speed was calculated by determining the amount of stone fragmented per second (mm³/second).

Postoperative CT scans were carried out at 3 months follow-up to check for residual stone presence, location, and size. Residual stone volumes were calculated using the formula π × L × W × H × 0.167.²³ To determine the percentage of stone reduction, the primary and secondary stone volumes were subtracted, and the result was divided by the primary volume, then multiplied by 100. Two cutoffs were used to report the stone-free rate (SFR) as a percentage: no visible remnants (zero fragments) and fragments <4 mm in size.^24,25

Some patients with a high stone burden underwent a postoperative CT scan at 4 weeks before stent removal to assess the need for a second look ureteroscopy. The impact of each laser on different stone compositions was recorded and analyzed. In addition, postoperative complications were closely monitored over 90 days and recorded, including emergency room visits, complaints during follow-up visits, and imaging results that indicated a complication.

In our study, continuous variables were expressed as medians and ranges, whereas categorical variables were described using frequencies and percentages. Statistical analysis was carried out using IBM^® SPSS^® Software version 23. To compare differences between the two groups, the following tests were used: the chi-squared test, Fisher's exact test, and Pearson's χ² test for categorical variables, the independent sample t-test for normally distributed continuous variables, and the nonparametric Mann-Whitney U-test for non-normally distributed data. A p-value of <0.05 was considered statistically significant.

Results

Initially, 129 eligible cases were identified, of which 111 were ultimately included in the study while 18 were excluded owing to missing data. The MOSES and TFL groups consisted of 62 and 49 patients, respectively. The median patient age was 65 years in the MOSES group and 63 years in the TFL group (p = 0.22). Most patients resumed anticoagulant or antiplatelet therapy as per their cardiac risk and literature recommendations.²⁶ Eleven participants (17.7%) in the MOSES group and 8 patients (16.3%) in the TFL cohort (p = 0.84) underwent operation without stopping their anticoagulant or antiplatelet therapy. There were no significant differences in clinical characteristics between the groups. Preoperative HN was detected in 27 cases (43.5%) in the MOSES group compared with 26 cases (53.1%) in the TFL group (p = 0.32). Preoperative ureteral stenting was performed for eight patients in each group (p = 0.61) because of fever or intractable pain. The individual clinical features and preoperative stone metrics are given in Table 1.

Table 1.

Participant Clinical Characteristics and Preoperative Stone Metrics

	MOSES (62 patients)	TFL (49 patients)	p
Gender, n (%)
Male	35 (56.5)	25 (51.0)	0.57
Female	27 (43.5)	24 (49.0)
Age (years), median (range)	65 (25–94)	63 (24–80)	0.22
BMI (kg/m²), median (range)	21.75 (17–41)	22.5 (16–35)	0.77
ASA class, n (%)
I	34 (54.8)	24 (49)	0.47
II	23 (37.1)	23 (46.9)
III	5 (8.1)	2 (4.1)
Anticoagulant or antiplatelet, n (%)	11 (17.7)	8 (16.3)	0.84
Side of operation, n (%)
Right	24 (38.7)	20 (40.8)	0.19
Left	38 (61.3)	29 (59.2)
Preoperative stent, n (%)	8 (12.9)	8 (16.3)	0.61
Preoperative hydronephrosis, n (%)	27 (43.5)	26 (53.1)	0.32
Stone site, n (%)
Upper pole	7 (11.3)	5 (10.2)	0.16
Middle pole	6 (9.7)	2 (4.1)
Lower pole	27 (43.5)	16 (32.7)
Pelvis	18 (29.0)	25 (51.0)
Occupying >1 location	4 (6.5)	1 (2.0)
Stone size (mm), median (range)	11.7 (4–39)	10.9 (5–31)	0.13
Stone volume (mm³), median (range)	436.5 (19–4795)	529 (52–4326)	0.57
Stone density (HU), median (range)	667 (211–1287)	668 (218–1604)	0.48

BMI = body mass index; HU = Hounsfield units; TFL = thulium fiber laser.

Intraoperative variables

Reusable URS was used in 37 cases (59.7%) in the MOSES group and 25 cases (51%) in the TFL group (p = 0.36). MOSES lasers were mostly set at 0.4–0.5 J and 70 Hz for dusting and 1 J and 10 Hz for fragmentation, whereas TFL lasers used 0.1–0.2 J and 100–200 Hz for dusting and 1 J × 10 Hz for fragmentation. Dusting was the commonly used technique in >70% of cases. To ensure consistency among all participating urologists, the optimal laser settings for various conditions were standardized and saved as pre-sets in the machine.

Efficiency measures

The median laser energy consumed in the MOSES group was 10.9 kJ and 9.8 kJ in the TFL group (p = 0.43). The median lasing time was 6.1 minutes for MOSES and 6.2 minutes for TFL (p = 0.47), and the median OR time was 55.5 minutes for MOSES and 60 minutes for TFL (p = 0.56). The median ablation efficiency was 17 J/mm³ for both the MOSES and TFL cohorts (p = 0.36). The median ablation speed was 1.4 mm³/second for MOSES and 1.6 mm³/second for TFL (p = 0.17). No statistically significant differences were observed in efficiency-related variables between MOSES and TFL. Table 2 provides a comparison of intraoperative variables and efficiency outcomes between the groups.

Table 2.

Intraoperative Variables and Efficiency Measures

	MOSES (62 patients)	TFL (49 patients)	p
Energy (kJ), median (range)	10.9 (0.1–39.2)	9.8 (0.3–28.2)	0.43
Lasing time (minutes), median (range)	6.1 (0.2–21)	6.2 (0.1–21)	0.47
OR time (minutes), median (range)	55.5 (18–135)	60 (25–121)	0.56
Ureteroscopy time (minutes), median (range)	31.5 (11–77)	34 (14–80)	0.25
Ablation efficiency (J/mm³), median (range)	17 (0.5–171.5)	17.2 (1.92–147.4)	0.36
Ablation speed (mm³/second), median (range)	1.4 (0.15–23.4)	1.6 (0.23–9.8)	0.17
Access sheath insertion, n (%)	44 (70.9)	35 (71)	0.95
Postoperative ureteral stent, n (%)	45 (72.6)	36 (73.4)	0.91

OR time = operative time.

Clinical outcomes

The 3-month postoperative SFR, with a fragment cutoff <4 mm, was 85.5% for the MOSES group and 87.8% for TFL (p = 0.73). When using a criterion of no visible fragments, the SFR was 42% for MOSES and 36.7% for TFL (p = 0.58). The median stone reduction was 99% and 97% for MOSES and TFL, respectively. No appreciable difference was observed between the groups in terms of outcomes.

We recorded six cases of stent-related storage symptoms in the TFL group and four incidents in the MOSES group, which were managed expectantly (Clavien I). Clavien II complications included patients who presented with a urinary tract infection and were treated with oral antibiotics. There were two cases of observed ureteral injury in the MOSES group (one grade I and one grade II according to the endoscopic ureteral injury grading). In the TFL group, a single case of ureteral injury grade I was observed. All instances of suspected ureteral injury were treated with ureteral stent insertion. No significant difference in 90-day complication rates was observed between the groups. Six patients (three in each group) required retreatment and a second look ureteroscopy, all of whom had a preoperative stone size >20 mm and a high postoperative residual stone burden (>10 mm). Table 3 outlines the clinical outcomes and complications.

Table 3.

Comparison of Outcomes and Complications

	MOSES (62 patients)	TFL (49 patients)	p
Stone-free rate, n (%)	53 (85.5)	43 (87.8)	0.73
Stone-free size, n (%)
0 mm	26 (42)	18 (36.7)	0.58
>0–3.9 mm	27 (43.5)	25 (51.1)	0.43
% Stone reduction, median (range)	99 (29–100)	97 (13–100)	0.91
Complications
Clavien I	4 (6.4)	6 (12)	0.63
Clavien II	2 (3.2)	3 (6)
Clavien III	0	0
Retreatment, n (%)	3 (4.8)	3 (6.1)	0.766
Stone composition, n (%)
COM	34 (54.8)	22 (44.9)	0.35
COD	8 (12.9)	6 (12.2)
CP	10 (16.1)	10 (20.4)
Urate	4 (6.5)	9 (18.4)
Cystine	5 (8.1)	2 (4.1)
Struvite	1 (1.6)	0 (0)

COM = calcium oxalate monohydrate; COD = calcium oxalate dihydrate; CP = calcium phosphate.

Analysis of efficacy measures was conducted for each stone composition. Ten cases of calcium phosphate stones were reported in each group (16.1% and 20.4% in the MOSES and TFL groups, respectively). The analysis revealed a statistically significant difference in the lasing time between the two groups when encountering calcium phosphate stones, with a median lasing time of 7.95 minutes for MOSES and 10.85 minutes for TFL (p = 0.01). Three cases of calcium phosphate stones did not respond properly to TFL, necessitating a switch to MOSES technology. The results are presented in Table 4.

Table 4.

Stone Composition and Efficiency Measures Across Different Stone Types

Parameter	MOSES (62 patients)	TFL (49 patients)	p
COM
Stone volume (mm³), median (range)	376.5 (42–4795)	353 (52–3633)	0.73
Stone density (HU), median (range)	726.5 (215–1179)	714.5 (302–1384)	0.48
OR time (minutes), median (range)	56.5 (18–135)	57.5 (26–110)	0.93
Ureteroscopy time (minutes), median (range)	30 (11–77)	34 (17–62)	0.5
Energy (kJ), median (range)	8.6 (0.1–39.2)	6.47 (0.3–28.2)	0.42
% Stone reduction, median (range)	97.5 (29–100)	99 (13–100)	0.58
Ablation efficacy (J/mm³), median (range)	17.6 (0.5–172.5)	18.9 (2.03–551.5)	0.68
Lasing time (minutes), median (range)	4.6 (0.2–21)	4.4 (0.1–12)	0.39
Ablation speed (mm³/second), median (range)	1.4 (0.21–22.9)	1.53 (0.05–9.46)	0.29
COD
Stone volume (mm³), median (range)	595 (19–1118)	552.5 (113–3239)	0.85
Stone density (HU), median (range)	843 (211–1275)	581.5 (401–1044)	0.49
OR time (minutes), median (range)	50.5 (32–91)	59 (38–106)	0.57
Ureteroscopy time (minutes), median (range)	24.5 (15–54)	36.5 (23–56)	0.22
Energy (kJ), median (range)	10.3 (1.8–32.44)	15.7 (4.3–18.8)	0.66
% Stone reduction, median (range)	98.5 (62–100)	95 (79–100)	0.85
Ablation efficacy (J/mm³), median (range)	25.6 (12.9–95.8)	20.1 (4.7–147.4)	0.49
Lasing time (minutes), median (range)	6.4 (1–15.8)	6.15 (2–7)	0.85
Ablation speed (mm³/second), median (range)	1.19 (0.32–2.59)	1.33 (0.31–8.4)	0.66
CP
Stone volume (mm³), median (range)	881 (53–4365)	740 (271–3978)	0.99
Stone density (HU), median (range)	730 (420–1287)	837 (271–1604)	0.68
OR time (minutes), median (range)	46.5 (28–64)	60 (25–69)	0.22
Ureteroscopy time (minutes), median (range)	32 (13–43)	33 (24–42)	0.68
Energy (kJ), median (range)	11.9 (6.8–18.8)	16.3 (8.7–24.98)	0.11
% Stone reduction, median (range)	100 (78–100)	93 (25–100)	0.48
Ablation efficacy (J/mm³), median (range)	13.2 (4.3–71.5)	22.2 (5–56.38)	0.85
Lasing time (minutes), median (range)	7.95 (4–11)	10.85 (6.3–21)	0.01
Ablation speed (mm³/second), median (range)	1.47 (0.15–6.6)	1 (0.23–6.65)	0.58
Uric acid
Stone volume (mm³), median (range)	570 (227–948)	444 (256–1472)	0.71
Stone density (HU), median (range)	316.5 (256–533)	363 (218–835)	0.5
OR time (minutes), median (range)	70 (38–85)	69 (35–83)	1
Ureteroscopy time (minutes), median (range)	37.5 (20–42)	34 (14–80)	0.38
Energy (kJ), median (range)	11.95 (9.9–31)	7.23 (4.9–19.79)	0.2
% Stone reduction, median (range)	94.5 (49–100)	94 (65–100)	0.94
Ablation efficacy (J/mm³), median (range)	28.8 (10.41–46.34)	21 (10.4–42.78)	0.5
Lasing time (minutes), median (range)	5.7 (4.8–15)	3.8 (2.3–12.2)	0.11
Ablation speed (mm³/second), median (range)	1.1 (0.35–2.9)	1.95 (0.98–4.16)	0.41

Discussion

There is a growing body of literature comparing the efficacy and clinical outcomes of TFL lithotripsy vs Ho:YAG. In this retrospective study, we compared the efficiency measures and outcomes of f-URS and laser lithotripsy utilizing pulse-modulated holmium laser with either MOSES or SOLTIVE SuperPulsed TFL for renal stones. Both groups had similar baseline demographic characteristics and stone metrics. Our analysis showed no significant difference in the efficiency determinants between the two groups, including operative time, ureteroscopy time, and lasing time. Our analysis showed no significant differences in the efficiency measures, such as laser energy, ablation speed, and efficacy, between MOSES and TFL. Moreover, both lasers demonstrated comparable performance during renal calculi lithotripsy.

In a prospective randomized controlled trial, Ulvik and colleagues¹⁸ compared the efficacy of SuperPulsed TFL and 30-W Ho:YAG laser in treating renal and ureteral stones >5 mm. The study found that the median operative time was significantly longer in the holmium group (60 minutes) compared with the TFL group (49 minutes; p = 0.008). Although laser energy was the only reported efficiency measure in their study, it was comparable between the two groups (median 2 vs 1.9 kJ for holmium and TFL, respectively, p = 0.4). In addition, their study demonstrated a significantly higher SFR in TFL-treated renal stones compared with holmium, regardless of whether a 3 mm cutoff was considered (92% vs 67% in TFL vs holmium, p = 0.001) or zero fragments (80% in TFL vs 57% in holmium, p = 0.006).

Conversely, in our study, we did not observe any significant differences in OR time, laser energy, or SFR between the two laser groups. It is possible that the maximum 30-W output of the holmium laser used in Ulvik and colleagues study contributed to the contrasting results.

Haas and colleagues²² conducted a randomized trial on 108 patients who underwent ureteroscopy for renal stones <20 mm, comparing the use of TFL and MOSES technology. Identical settings of 0.8 J and 8 Hz were used for fragmentation and 0.3 J and 80 Hz for dusting for both lasers, with the energy adjusted as needed. The observed zero fragment SFR, mainly assessed by kidney, ureter, and bladder radiograph (KUB), was 68% for the MOSES group and 67% for TFL, with similar ureteroscopy and lasing times between the two groups. In addition, the ablation speed was comparable between the two lasers. However, TFL used significantly more energy to ablate a cubic millimeter of stone (median 1.8 J/mm³ in TFL vs 1.5 J/mm³ in MOSES; p = 0.009). Of interest, the surgeons' subjective evaluation of laser performance showed that TFL was perceived as better in terms of retropulsion, efficiency, and ease of fiber passage through the ureteroscope. However, there was no significant difference in perceived durability, reliability, and laser flexibility.

Patil and coworkers²¹ conducted a prospective propensity score-matched study to compare the efficacy of high-power holmium laser with MOSES technology and SuperPulsed TFL in managing renal stones <3 cm with vacuum-assisted mini-percutaneous nephrolithotomy. SFR was evaluated by KUB, ultrasound, or CT scan at 48 hours postoperatively and 1 month follow-up. The study found similar SFR at 48 hours (78.43% with MOSES and 68.63% with TFL, p = 0.17) and comparable ablation speed (4.6 vs 5.2 mm³/second in MOSES and TFL, respectively). However, TFL left a greater proportion of fragments >3 mm compared with MOSES (36% vs 22.68%, p = 0.002). In a subset analysis based on stone density, the study revealed comparable outcome and efficiency measures except for a shorter operative time with TFL (p ≤ 0.05).

A recent study conducted by Yang and associates²⁷ prospectively compared the ablation rates of TFL and MOSES in vitro and found that despite TFL's higher ablation rate because of its wavelength, recent updates to the holmium system have made it just as efficient in some cases. The study also revealed that higher frequencies achieved with TFL do not enhance its ablation speed. In addition, the authors noted that the MOSES lithotripsy effect is less reliant on the working distance (i.e., the distance between the laser fiber tip and stone surface) compared with TFL and regular high-power holmium laser.

Our study has several distinctive features. First, we relied solely on CT scans for stone remnant detection, which provided the most precise SFR outcomes compared with studies that utilized other imaging modalities such as ultrasounds and abdominal X-rays. Second, we used stone analysis to investigate the potential benefits of one laser over the other while ablating different types of stones. The evaluation of efficiency for various stone subtypes revealed that both lasers performed comparably, except in the case of calcium phosphate stones, where TFL required significantly more lasing time than MOSES.

Our study has some limitations. First, our observations were derived from a retrospective analysis with a relatively small sample size. Ideally, a randomized controlled trial involving uniform-sized stones and laser-only treatment (without basketing), until no significant residues remain, would be the optimal approach to compare the ablation efficiency measures of different lasers. However, this limitation is not unique to our data, and other researchers face similar constraints. Finally, the analysis of calcium phosphate stones was limited because of the small number of cases, leading to underpowered statistical analysis, which may restrict the generalizability of our findings.

Conclusions

Both high-power pulse-modulated holmium MOSES and TFL were similarly effective for URS lithotripsy of renal stones. Holmium MOSES demonstrated enhanced laser efficiency for calcium phosphate stones; however, there was no difference in the final operative time. Given our study's limited patient population, additional research with larger sample sizes is required to validate our findings.

Footnotes

Acknowledgment

The abstract was previously published in Canadian Urological Association 2023 Annual Meeting Abstracts, Montreal, June 25, 2023 (doi: 10.5489/cuaj.8419).

Authors' Contributions

P.N.: Data collection, statistical analysis. A.H.: Statistical analysis and article editing. M.F.: Data collection and management. A.S.Z.: Protocol/project development and article writing. W.S.: Article editing. R.A.H.: Article editing. I.F.A.: Article writing. H.A.: Article editing. L.A.: Article writing. A.A.: Project development and article editing. W.S.: Article editing. H.E.: Protocol/project development and article writing.

Author Disclosure Statement

No conflict of interest.

Funding Information

No funding was received for this article.

Abbreviations Used

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