OUTCOME AND SAFETY OF THULIUM FIBER LASER FOR URINARY STONE DISEASES - A CROSS-SECTIONAL STUDY

Thulium ﬁber laser (TFL) was introduced into the urological armamentarium as an alterna�ve to Ho:YAG as an energy source. This study aims to assess the outcome and safety of RIRS using TFL in pa�ents with proximal ureteric and renal stone requiring interven�on.


INTRODUCTION
Nephrolithiasis is a global problem affec ng all geographical regions with prevalence of 3-5% and the life me prevalence is 15-25%. Nephrolithiasis has propensity to recur in most of the pa ents. Recurrence rates of renal stone are about 10% per year, 50% over a period of 5-10 years and 75% over 20 1 years period . The rate of recurrence of renal calculi in pa ents a er 1st me occurrence is 14% at 1st year, 35% in th 2 5th year and 52% in 10 year. In our set up, about 50% of our outpa ents are of urinary stone disease. Symptoma c pa ents with urinary stone disease require treatment and the op ons are conserva ve management, endourological management, laparoscopic surgery or open surgery. Endourological procedures are the most commonly performed procedure in the urinary stone treatment depending upon the size, loca on and density and available armamentarium either in the form of ureteroscopy and lithotripsy (URSL), percutaneous nephrolithotomy (PNL) or retrograde intrarenal surgery (RIRS) using flexible scope and 3 laser as energy source . Currently, Holmium:YAG and thulium fiber laser (TFL) are most commonly used lasers in urology for stone disease. Thulium fiber laser is a pulsed laser with wavelength of 1940nm was introduced into the 4 urological prac ce in 2018 . It came as an alterna ve to Ho: YAG. Emi ng pulsed infrared light at a wavelength of 1940 nm, which is close to the water absorp on peak, a fourfold higher absorp on coefficient is achieved with TFL compared to Ho:YAG, corresponding to a low threshold for ssue abla on and stone lithotripsy . Cavita on bubble dynamics also differ from Ho:YAG, and TFL produces a stream of bubbles smaller than those seen with Ho:YAG use . TFL is therefore expected to be very efficient at disintegra ng 5,6 stones in clinical prac ce . Compared to Ho:YAG, TFL has the ability to func on at very low energies and extremely high frequencies making it more versa le. In vitro study has shown that TFL works 4-5 mes faster, produces finer dusts, has hemosta c proper es and produces less fiber burn back 7 compared to Ho: YAG . The RIRS usingHo:YAGis a common procedure in our prac ce for proximal ureteric and renal stones but we introduced TFL in our ins tu on in the July 2022. This study aims to assess the outcome and safety of RIRS using TFL in pa ents with proximal ureteric and renal stone diseases requiring minimally invasive interven on at Birat Medical College-Teaching Hospital. We included adult pa ents with stone size up to 20 mm. We excluded pa ents with ac ve urinary infec on, coagulopathy, stone size > 20mm.

METHODOLOGY
Pa ents were evaluated preopera vely as per ins tu onal protocol. All pa ents were presented using 6F, 26 cm double J (DJ) stent and they received prophylac c an bio cs as per ins tu onal protocol or culture sensi vity report. The procedure was done either in general or spinal anesthesia. Semirigid ureteroscopy using 6.5/7 Fr ureteroscope from Karl Storz was done in all pa ents before introduc on of ureteral access sheath (10.7/12.7 Fr, Cook Medical) or 7.5Fr flexible scope (BioradMedisys, India). Calculus was dusted, fragmented or popcorned using 60W laser machine (UROLASE SP+, IPG, Russia) and 200-micron laser fiber with energy and frequency range of 0.2-1.2J and 50-125Hz respec vely. At the end of procedure, 6F 26cm DJ sten ng was done in all pa ents and they received an bio cs, proton pump inhibitor, analgesics and alpha-blocker (Tamsulosin 0.4mg po HS). X-ray KUB was done next morning & pa ents were discharged on oral an bio cs and other symptoma c treatments unless any complica on occurred. Pa ents' demography, stone status (loca on, size, volume and density), opera ng me, hospital stay and complica ons recorded. DJ stent removal was done @ 2weeks. Stone clearance was assesed @6 weeks postopera vely via Ultrasound, any residual fragment >2mm was considered significant (CSRF). Sta s cal analysis was performed using SPSS Sta s cs version 27 (IBM, Armonk, NY). Con nuous and ordinal variables were expressed as mean ± standard devia on and nominal variables were expressed as frequency and percentage. Comparison of propor ons was done by chisquare test and con nuous data by t-test. P values of < 0.05 were considered as sta s cally significant.

RESULTS
We included the ini al 50 cases. The baseline characteris cs are men oned below.

DISCUSSION
This study was designed to assess the outcome and safety of RIRS using TFL as an energy source in the clinical prac cein pa ents with proximal ureteric and renal stonebeing inspired by the results of preclinical studies. In this study, mean age of the pa ents was 40.02± 13.97 years with male predominance ( 66%) and majority of the calculus were on right side ( 58%). In this study, mean age of the pa ents was 40.02± 13.97 years with male predominance (66%)and majority of the calculus were on the right side (58%). This is comparable with the study of Vaddi et al where mean age of the pa ents was 45.04±12.30 years with 8 male predominance (60.3%) and right sided loca on (59%) . The mean stone size in this study was 14.45±3.36mm (range 9mm-20mm). This similar to the studies conducted in India and Russia where the mean stone size was 15.19±4.52 mm and 8,9 16.5 ± 6.8 mm respec vely. Similarly, the mean stone density was 1046.96±236.88 HU in the current study. This was slightly higher than the study of Vaddi et al where it was 985.82±302.57 HU and the study of Enikeev et al where it 8,9 was 880 ± 381 HU. But it was lower than the study of 7 Corrales et al with median density of 1200 (750-1300) HU. Since HU is a rela ve measurement, it can vary across the centres depending upon mul ple factors which explains the varia ons in the stone density in the studies. The mean 3 stone volume in our study was 534.46±209.53 mm. This volume is lower than the study of Corrales et al ( median- respec vely. The lower volume in our study can be due to the manual calcula on of the volume by the repor ng Radiologist as volume es ma on so ware was not available in the CT scan available in our centre. The mean flexible ureteroscopy on me in our study was 16.32±5.18 minutes. This is less than other similar study 8 (33.21±16.05 minutes. This difference can be because of difference in turning on of flexible scope. In the current study, the scope was introduced on fluoroscopic guidance and a er entering into the pelvicalyceal system it was turned on. Further, it was turned off soon a er the abla on was completed. Other similar studies have not commented [9][10][11] upon the scope on me. A er 6 weeks post procedure, complete stone clearance was achieved in 46 cases (92%). It was comparable with other studies in similar se ngs with stone free rate of 8,9,11 93.6%, 89% and 92.5% respec vely. However, they assessed stone clearance at 3 months a er surgery with CT scan. The stone clearance with TFL was higher than Ho:YAG using either regular or mosses technology with 83.3% and 12 88.4% clearance respec vely for each technology. It indicates superiority of TFL over Ho:YAG. The CSRF was seen in 4 of our cases (8%) and they all opted for conserva ve approach. Complica on occurred in our 6 cases (12%) and they all were post procedure urosepsis and recovered a er DJ stent removal (Clavien IIIa

CONCLUSION
The TFL as a newer energy source is safe and effec ve for lithotripsy during RIRS with acceptable complica ons.

RECOMMENDATION
We recommend further clinical studies to ensure op mal comparison with conven onal Ho:YAG lithotripsy.

LIMITATION OF THE STUDY
This study is limited by being single centre study, shorter follow up dura on and not using CT scan to assess stone clearance. The efficiency of TFL can be evaluated by laser efficacy and abla on speed which was not used here. Further, we did not compare its efficacy with respect to stone density and volume which can be another limita on of this study.