The purpose of this study is to compare two laser technologies that are routinely used during ureteroscopy for the treatment of kidney stones. Specifically, this study will compare a pulsed Thulium:YAG laser to a pulse-modulated Holmium:YAG laser (Moses technology) to evaluate how effective and safe they are when used to break kidney stones.

Primary endpoints include stone-free rate and the zero stone-free rate at a standardized postoperative. Secondary endpoints include total operative time, lasing time (s), laser energy expended (J), efficiency (laser energy expended/stone volume; stone volume/lasing time). These endpoints aim to provide a comprehensive assessment of the clinical effectiveness and procedural efficiency of the two laser systems.

Inclusion Criteria:

• Solitary renal stone 7 to 20 mm in size or in the case of multiple stones the conglomerate diameter (additive maximal diameter of all stones on axial imaging of computed tomography) of 7-20 mm is required
• Must be a suitable operative candidate for flexible ureteroscopy per American Urological Association guidelines
• Must be 18 years or older
• Must be able to give consent
• Bilateral ureteroscopy will be permitted , but only the side(s) where the FANS access sheath was used (per surgeon discretion) will be included in the study, however can include both sides as separate units. Subjects will be enrolled only once in the study. No subject will be enrolled more than a single time. For patients undergoing bilateral ureteroscopy, each kidney will be considered a separate unit for stone-related assessments. Peri-patient measures, such as operative time, will be recorded at the patient level. Bilateral cases will be clearly identified and handled consistently to ensure accurate and appropriate interpretation of study outcomes.
• Must be a patient of one of the surgeons participating in this study.

Exclusion Criteria:

• Concomitant stones in the ureter
• Prior radiotherapy to the abdomen or pelvis
• Neurogenic bladder or spinal cord injury
• Pregnancy
• Untreated urinary tract infection (UTI)
• Anatomical abnormalities (including, but not limited to, bifid system, pelvic kidney, horseshoe kidney)
• Prior ipsilateral upper urinary tract reconstructive procedures or history of ipsilateral ureteral stricture

The de-identified participant data from the final research dataset will be shared to achieve aims in the approved proposal beginning 9 to 36 months after publication or as required by a condition of awards or supporting agreements, provided the requesting researcher provide a methodologically sound proposal and executes a data use agreement with NYU Langone Health. This instance of data sharing will also require separate IRB review as well as review from NYU Langone's Data Sharing Strategy Board (DSSB). Requests should be directed to: esteban.emilianisanz@nyulangone.org. The protocol and statistical analysis plan will be posted on Clinicaltrials.gov only as required by federal regulation or supporting awards and agreements.

Beginning 9 months and ending 36 months following article publication or as required by a condition of awards and agreements supporting the research.

Researchers who provide a methodologically sound proposal will be granted access to achieve aims in the approved proposal. Requests should be directed to esteban.emilianisanz@nyulangone.org. To gain access, data requestors will need to sign a data access agreement. This instance of data sharing will also require separate IRB review as well as review from NYU Langone's DSSB.

The case coordinator will inform the operating surgeon of the assigned laser before the procedure begins. Study participants will remain blinded to the laser assignment. Outcome assessments, including imaging based evaluation, will be performed by personnel who are blinded to treatment allocation.