Endourological management of urolithiasis has advanced rapidly with the introduction of new tools and technologies aimed at improving existing treatments [1]. These innovations have enabled more complete clearance of stones with shorter hospital stays, reduced need for auxiliary procedures, and fewer complications [2]. The holmium: yttrium-aluminum-garnet (Ho:YAG) laser has long been regarded as the gold standard for ureterorenoscopic (URS) lithotripsy, revolutionizing the management of urolithiasis over the past two decades because of its ability to effectively fragment all types of stones [3]. However, Ho:YAG has limitations, including bulky machine ,;size, relatively low energy efficiency, and difficulty in focusing the laser beam through small-diameter fibers. Recently, the thulium fiber laser (TFL) has been introduced as a potential alternative to Ho:YAG, offering several advantages. Operating at a wavelength of 1940 nm, close to the peak absorption of water, TFL achieves a fourfold higher absorption coefficient than Ho:YAG, resulting in a lower ablation threshold for both tissue and stone lithotripsy [4]. Unlike the solid-state Ho:YAG system, TFL employs a diode-pumped silica fiber, allowing for delivery of high-power output through smaller fibers, which increases intensity and improves the stone ablation rate [5]. In addition, the cavitation bubble dynamics differ between the two systems. TFL generates smaller bubbles compared to Ho:YAG, a feature believed to enhance the efficiency of stone disintegration [6]. Laboratory studies have suggested that TFL may ablate stones up to four times faster than Ho:YAG when equivalent energy settings are used [7]. TFL is also capable of operating at very low pulse energies and extremely high frequencies, though optimal efficiency in clinical practice is often achieved at moderate energy settings, similar to those commonly used with Ho:YAG. Despite promising preclinical data, clinical studies on TFL remain limited [8]. Whether the encouraging laboratory results translate into clinical superiority is still uncertain, and few trials have directly compared the efficacy and safety of TFL with Ho:YAG in ureteric stone management. Based on the hypothesis that TFL may yield superior outcomes, we conducted a prospective randomized clinical trial with the primary aim of comparing stone-free rates (SFRs) following URS lithotripsy using Ho:YAG and TFL for ureteral stones. Secondary objectives were to compare operative time, perioperative complications, and the rate of post-endoscopic ureteral stenting between the two laser modalities.

Study Design and Setting This was a single-center, randomized, prospective controlled trial conducted in the Department of Urology, Mamata Medical College and Hospital, Khammam, Telangana. The study was hospital-based and carried out over a duration of 24 months, from September 2022 to October 2024, after obtaining approval from the Institutional Ethics Committee. Study Population The study population consisted of patients with ureteral stones who attended the Department of Urology, Mamatha Medical College and Hospital, Khammam, Telangana, and were scheduled to undergo surgical intervention. Inclusion Criteria Patients of both sexes, aged above 18 years, with ureteral stones larger than 5 mm confirmed by abdominal and pelvic computed tomography, were included. All patients were treated with rigid ureteroscopy and underwent laser lithotripsy during the procedure. Exclusion Criteria Patients were excluded if laser was not used for lithotripsy, if they were pregnant, younger than 18 years, or refused to provide informed consent. Additional exclusions included prior upper tract reconstruction (such as urinary diversion, ureteral reimplantation, or pyeloplasty), presence of urinary tract anomalies (solitary kidney, horseshoe kidney, ectopic kidney, mal-rotated kidney, duplex collecting system, or UPJ obstruction), and those with conditions deemed unsuitable for study participation. Intervention and Randomization The intervention consisted of rigid ureteroscopy for ureteral stone lithotripsy using either holmium:YAG (Ho:YAG) or thulium fiber laser (TFL). A total of 100 patients were recruited and randomized in a 1:1 ratio into the Ho:YAG or TFL group using block randomization in blocks of four. Randomization was concealed in consecutively numbered, sealed envelopes, which were opened only after patient consent and allocation immediately prior to surgery. No blinding of patients or surgeons was feasible, as the laser platforms had clearly distinct features. However, sharing allocation details with patients was not considered to influence primary or secondary outcomes. Methodology and Data Collection After obtaining ethical clearance, informed written consent was collected from all participants. Patients were explained the purpose, implications, and outcomes of the study in their native language, and were assured that participation was voluntary and would not affect their treatment process. A structured patient data entry form was designed to capture demographic data (age, sex, weight, and height), medical history (comorbidities such as coronary artery disease, hypertension, diabetes, obesity, gout, hyperparathyroidism, prior urinary tract infections, or previous stone history), and urolithiasis details (stone laterality, number, size, burden, volume, and density in Hounsfield units). Intraoperative and Laser Parameters Data recorded during surgery included ASA score, use of ureteric dilation or access sheath, and stent details. Operative time was measured from placement of the guidewire to final stent positioning. Laser settings, including energy, frequency, power output, total energy used, laser-on time, fiber type, and changes during the procedure, were documented. Calculated measures included ablation efficiency (J/mm³) and ablation speed (mm³/s). Postoperative Data and Follow-up All patients were managed as day-care procedures unless complications warranted admission. Postoperative complications were recorded up to 30 days using the Clavien-Dindo classification. The stone-free rate (SFR) at three months was assessed by non-contrast CT scan and graded as per Endourological Society standards (Grade A: stone-free, Grade B: <2 mm fragments, Grade C: 2.1–4 mm fragments). Outcome Measures The primary outcome was the stone-free rate three months after surgery. Secondary outcomes included perioperative complications, operative time, and postoperative complications up to three months after surgery. Statistical Analysis All data were entered into Microsoft Excel and analyzed using SPSS software (trial version 23). Descriptive statistics summarized quantitative variables, with standard deviation used as a measure of variation. Qualitative variables were expressed as percentages with 95% confidence intervals. Between-group comparisons of means were performed using Student’s t-test or Mann–Whitney test where appropriate. Proportions were compared using Chi-square or Fisher’s exact test. A p-value <0.05 was considered statistically significant. Ethical Considerations The study adhered to the guidelines of the Indian Council of Medical Research (1994) and the Helsinki Declaration (modified 2000). All participants were fully informed about the aims, methodology, risks, and benefits of the study, as well as the voluntary nature of their participation. Confidentiality and privacy were maintained at all stages, with patients retaining the right to withdraw at any time without affecting their care. No treatment options were withheld, and all patients were managed according to standard departmental protocols. Informed consent was obtained from every participant, and all precautions were taken to minimize risks and ensure patient safety.

Table 1: Distribution of Subjects According to Age and Gender between Groups Variable Category Ho:YAG Group (n=50) TFL Group (n=50) Total (n=100) p-value Age < 50 years 0 (0%) 1 (2%) 1 (1%) 50–59 years 10 (20%) 12 (24%) 22 (22%) 60–69 years 31 (62%) 31 (62%) 62 (62%) ≥ 70 years 9 (18%) 6 (12%) 15 (15%) Mean ± SD 63.8 ± 5.14 62.6 ± 5.67 63.2 ± 5.42 0.619 Gender Male 17 (34%) 19 (38%) 36 (36%) Female 33 (66%) 31 (62%) 64 (64%) Total 50 (100%) 50 (100%) 100 (100%) 0.677 The study population consisted of 100 patients, evenly divided between the Ho:YAG and TFL groups. The mean age was comparable between the two groups (63.8 ± 5.14 years vs. 62.6 ± 5.67 years, p=0.619), with the majority of patients falling in the 60–69 year age range (62% in both groups). In terms of gender distribution, males accounted for 34% in the Ho:YAG group and 38% in the TFL group, while females comprised 66% and 62% respectively; the difference was not statistically significant (p=0.677). Table 2: Distribution of Subjects According to Body Mass Index (BMI) Between Groups BMI Category (kg/m²) Ho:YAG Group (n=50) TFL Group (n=50) Total (n=100) p-value < 18.5 (Underweight) 0 (0%) 0 (0%) 0 (0%) 18.5 – 24.9 (Normal) 2 (4%) 2 (4%) 4 (4%) 25 – 29.9 (Overweight) 43 (86%) 41 (82%) 84 (84%) ≥ 30 (Obese) 5 (10%) 7 (14%) 12 (12%) Mean ± SD 27.6 ± 1.62 27.5 ± 1.73 27.6 ± 1.66 0.827 Most patients in both groups were overweight (BMI 25–29.9 kg/m²), accounting for 86% in the Ho:YAG group and 82% in the TFL group. A smaller proportion were obese (10% vs. 14%), and only 4% in each group had a normal BMI; none were underweight. The mean BMI was nearly identical between the groups (27.6 ± 1.62 vs. 27.5 ± 1.73, p=0.827), indicating no significant difference in body mass index distribution. Table 3: Distribution of Subjects According to Comorbidities Between Groups Comorbidity Ho:YAG Group (n=50) TFL Group (n=50) Total (n=100) p-value Coronary Artery Disease (CAD) 0 (0%) 2 (4%) 2 (2%) 0.153 Hypertension (HTN) 8 (16%) 12 (24%) 20 (20%) 0.056 Diabetes Mellitus (DM) 8 (16%) 6 (12%) 14 (14%) 0.564 Dyslipidemia 11 (22%) 6 (12%) 17 (17%) 0.183 History of Metabolic Abnormalities 6 (12%) 8 (16%) 14 (14%) 0.571 Total 50 (100%) 50 (100%) 100 (100%) Comorbidities were observed in both groups without significant differences. Hypertension was the most common condition, present in 16% of the Ho:YAG group and 24% of the TFL group. Diabetes mellitus was reported in 16% and 12% of patients, respectively, while dyslipidemia was seen in 22% and 12%. A history of metabolic abnormalities was noted in 12% of the Ho:YAG group and 16% of the TFL group. Only two cases of coronary artery disease were recorded, both in the TFL group. Overall, comorbidity distribution was broadly similar across groups, with no statistically significant differences. Table 4: Distribution of Subjects According to History of Urolithiasis Between Groups History of Urolithiasis Ho:YAG Group (n=50) TFL Group (n=50) Total (n=100) p-value Yes 34 (68%) 31 (62%) 65 (65%) No 16 (32%) 19 (38%) 35 (35%) Total 50 (100%) 50 (100%) 100 (100%) 0.529 A past history of urolithiasis was present in the majority of patients, observed in 68% of the Ho:YAG group and 62% of the TFL group, while 32% and 38% of patients in each group, respectively, had no such history. The difference between the two groups was not statistically significant (p=0.529). Table 5: Distribution of Subjects According to Stone Characteristics Between Groups Variable Category Ho:YAG Group (n=50) TFL Group (n=50) Total (n=100) p-value Side of Stone Right 30 (60%) 22 (44%) 52 (52%) Left 20 (40%) 28 (56%) 48 (48%) 0.109 Number of Stones 1 40 (80%) 38 (76%) 78 (78%) 2 8 (16%) 7 (14%) 15 (15%) 3 2 (4%) 5 (10%) 7 (7%) 0.496 Location of Stones Upper ureter 6 (12%) 7 (14%) 13 (13%) Mid ureter 10 (20%) 13 (26%) 23 (23%) Lower ureter 34 (68%) 30 (60%) 64 (64%) 0.133 The analysis of stone characteristics showed no significant differences between the Ho:YAG and TFL groups. With respect to the side of the stone, 60% of patients in the Ho:YAG group had right-sided stones compared to 44% in the TFL group, while left-sided stones were slightly more frequent in the TFL group (56% vs. 40%, p=0.109). Regarding the number of stones, a single stone was the most common presentation in both groups (80% Ho: YAG vs. 76% TFL), with smaller proportions having two or three stones, and no significant group difference (p=0.496). For the location of stones, the lower ureter was the predominant site in both groups (68% Ho: YAG vs. 60% TFL), followed by the mid and upper ureter, again with no statistically significant difference (p=0.133). Table 6: Distribution of subjects according to Urolithiasis Characteristics comparing between groups Urolithiasis Characteristics Mean ± SD Ho:YAG Group TFL Group Total p-value Stone burden, mm 13.7 ± 1.36 14.1 ± 1.74 13.9 ± 1.57 0.650 Stone volume, mm3 689.5 ± 69.25 708.9 ± 87.72 699.3 ± 79.23 0.523 Stone density, HU 1090.2 ± 109.52 1121.03 ± 138.71 1105.6 ± 125.29 0.522 The urolithiasis characteristics were comparable between the two groups. The mean stone burden was 13.7 ± 1.36 mm in the Ho:YAG group and 14.1 ± 1.74 mm in the TFL group (p=0.650). Similarly, the mean stone volume was 689.5 ± 69.25 mm³ and 708.9 ± 87.72 mm³, respectively (p=0.523). The mean stone density also showed no significant difference, being 1090.2 ± 109.52 HU in the Ho:YAG group and 1121.03 ± 138.71 HU in the TFL group (p=0.522). Overall, both groups were well matched in terms of stone characteristics. Table 6: Distribution of Laser-related Variables and comparing between groups Laser-related Variables Ho:YAG Group TFL Group Total p-value Total Operative Time (minutes) 36.8 ± 3.68 26.0 ± 4.66 32.4 ± 4.22 0.027 Laser-ON Time (seconds) 532.8 ± 53.55 440.7 ± 62.41 486.8 ± 57.99 0.035 Total Energy (Joules) 7459.5 ± 749.3 7570.2 ± 873.67 7514.9 ± 811.6 0.658 Ablation Speed (mm3/ s) 1.0 ± 0.10 2.1 ± 0.12 1.4 ± 0.11 0.618 Ablation Efficiency (J/ mm3) 11.1 ± 1.12 5.2 ± 1.30 8.2 ± 1.21 0.020 Table 6 shows the laser-related variables distribution of the subjects comparing between groups. The mean total operative time was 32.4 ± 4.22 minutes and there was significant differences in the total operative time between the subjects of Ho:YAG and TFL groups (36.8 ± 3.68 minutes vs 26.0 ± 4.66 minutes) (p-value = 0.027). The mean Laser-ON Time was 486.8 ± 57.99 seconds and there was significant differences in the Laser-ON Time between the subjects of Ho:YAG and TFL groups (532.8 ± 53.55 seconds vs 440.7 ± 62.41 seconds) (p-value = 0.035). The mean total energy was 7514.9 ± 811.69 J and there was no significant differences in total energy between the subjects of Ho:YAG and TFL groups (7459.5 ± 749.33 J vs 7570.2 ± 873.67 J) (p-value = 0.658). The mean Ablation Speed was 1.4 ± 0.11 mm3/ s and there was no significant differences in the Ablation Speed between the subjects of Ho:YAG and TFL groups (1.0 ± 0.10 mm3/ s vs 2.1 ± 0.12 mm3/ s) (p-value = 0.618). The mean Ablation Efficiency was 8.2 ± 1.21 J/ mm3 and there was significant differences in Ablation Efficiency between the subjects of Ho:YAG and TFL groups (11.1 ± 1.12 J/ mm3 vs 5.2 ± 1.30 J/ mm3) (p-value = 0.020). Table 7: Distribution of subjects according to Complications comparing between groups Complications Ho:YAG Group TFL Group Total Intra-operative complications (p-value = 0.416) Mucosal injury (grade 1) 12 (24%) 8 (16%) 20 (20%) Ureteric perforation 0 (0%) 0 (0%) 0 (0%) None 38 (76%) 42 (84%) 80 (80%) Postoperative complications (p-value = 0.628) Grade 1 pain 6 (12%) 6 (12%) 12 (12%) Grade 2 fever with change of antibiotics 2 (4%) 1 (2%) 3 (3%) Grade 3 stent removal for fever 1 (2%) 0 (0%) 1 (1%) Grade 4 0 (0%) 0 (0%) 0 (0%) Grade 5 0 (0%) 0 (0%) 0 (0%) None 41 (82%) 43 (86%) 84 (84%) Total 50 (100%) 50 (100%) 100 (100%) Table 7 shows the complications distribution of the subjects comparing between groups. Regarding the intraoperative complications, 20 subjects had Grade 1 Mucosal injury and no other complications were documented intraoperatively. This occurrence was not significantly higher in any group (p-value = 0.416). Regarding the postoperative complications, 12 subjects had pain, 3 subjects had fever with change of antibiotics and 1 subject had stent removal for fever and no other complications were documented postoperatively.

Since its introduction in 1992, the holmium: yttrium aluminum garnet (Ho:YAG) laser has been the gold standard for ureteroscopic lithotripsy because of its proven safety, efficacy, and durability. However, drawbacks such as limited energy efficiency, larger fiber size, stone retropulsion, and impaired endoscopic vision remain challenges. In contrast, the thulium fiber laser (TFL), introduced in 2018, offers advantages including a higher water absorption coefficient, smaller penetration depth, thinner and more flexible fibers, and improved stone dusting with reduced retropulsion, making it a promising alternative to Ho:YAG. In the present study, baseline patient characteristics such as age, gender, BMI, comorbidities, ASA status, and history of urolithiasis were well balanced across groups with no statistically significant differences (p>0.05). These findings are in agreement with prior randomized and prospective studies [9, 10], suggesting that patient profiles between Ho:YAG and TFL groups were comparable and unlikely to confound outcomes. Similarly, stone-related characteristics including stone burden, stone volume, density, laterality, number, and location did not differ significantly between the two groups. Comparable findings were also reported in previous meta-analyses and trials [11]. When analyzing laser-related parameters, important differences were observed. The mean operative time and laser-ON time were significantly shorter in the TFL group, reflecting its greater ablation efficiency and faster stone fragmentation. The ablation efficiency was also significantly superior in the TFL group (p<0.05). These observations support findings from earlier trials and reviews which consistently reported that TFL achieves faster stone disintegration with shorter operative and lasering times [12]. With respect to outcomes, the stone-free rate (SFR) at 3 months was comparable between the two groups, consistent with several randomized trials [13]. However, some studies [14] have suggested higher SFRs with TFL, which may be attributed to its finer dusting capability and reduced retropulsion. In our study, intraoperative and postoperative complications were minimal and did not significantly differ between groups, which is in line with prior systematic reviews and randomized trials [15]. Postoperative stone analysis and mean hospital stay were also comparable, echoing results from earlier studies [16, 17]. Overall, the present findings add to the growing body of evidence that TFL is at least as safe and effective as Ho:YAG, with additional procedural advantages that may translate into better efficiency and surgical ergonomics.

This study demonstrates that both TFL and Ho:YAG lasers achieve comparable stone-free rates and have similar safety profiles, but TFL offers significant procedural advantages, including shorter operative time, reduced laser-ON time, and superior ablation efficiency. These findings suggest that TFL may represent a more efficient and potentially superior alternative to Ho:YAG in endourological lithotripsy. With continued refinement of laser technology and larger multicentric studies, TFL may establish itself as the preferred modality for ureteroscopic lithotripsy in the future.

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