The goal of this prospective, multicenter, randomized controlled trial is to objectively evaluate the clinical efficacy and safety differences between superpulse thulium fiber laser (sTFL) and holmium:YAG laser (Ho:YAG) in flexible ureteroscopy (FURS) lithotripsy in adult patients aged 18-70 years with kidney stones and/or upper ureteral stones (6-20mm). The main questions it aims to answer are:

Does sTFL yield a higher stone-free rate (SFR) compared to Ho:YAG at 3 months post-FURS? Is sTFL superior to Ho:YAG in terms of operation time, complication rate, and surgeon's visual experience during FURS? Researchers will compare the experimental group receiving sTFL treatment to the control group receiving Ho:YAG laser treatment to see if sTFL demonstrates better lithotripsy efficiency, safety, and ease of operation.

Participants aged 18-70 years will:

Undergo FURS lithotripsy under general anesthesia using either sTFL (experimental group) or Ho:YAG laser (control group) based on randomization Have CT scans at 3 months post-operation to assess stone-free status Be monitored for intraoperative and postoperative complications Have surgeons rate their visual experience during the procedure in terms of visual clarity, lithotripsy efficiency, stone movement and tissue injury

Flexible ureteroscopy (FURS) has become a widely accepted minimally invasive treatment modality for kidney stones and upper ureteral stones. Holmium:YAG laser (Ho:YAG) is currently the gold standard for laser lithotripsy during FURS. However, the superpulse thulium fiber laser (sTFL) has emerged as a promising alternative with potential advantages in terms of lithotripsy efficiency and safety. This prospective, multicenter, randomized controlled trial aims to objectively evaluate the clinical efficacy and safety differences between sTFL and Ho:YAG in FURS for adult patients with kidney stones and/or upper ureteral stones (6-20mm).

The study will enroll 136 participants aged 18-70 years with confirmed diagnosis of kidney stones and/or upper ureteral stones (6-20mm) based on CT scans. Participants will be randomized in a 1:1 ratio to undergo FURS with either sTFL (experimental group) or Ho:YAG (control group). The primary outcome measure will be the stone-free rate (SFR) at 3 months post-operation, defined as residual fragments <2mm on CT scans. Secondary outcomes will include operation time, intraoperative complications (e.g., ureteral injury, bleeding, infection), postoperative complications (e.g., fever, hematuria), changes in vital signs, surgeon's visual experience, and stone recurrence rate at 6 months.

Participants will be closely monitored for adverse events and complications throughout the study period. The Clavien-Dindo classification system will be used to grade postoperative complications. Detailed safety assessments will be performed, including recording of adverse events, reporting of serious adverse events, monitoring of vital signs, and evaluation of complications.

The study will consist of the following visits:

Baseline visit (screening period): Participants will provide informed consent, undergo eligibility assessment, and have their demographic information, medical history, vital signs, and CT scans collected.

Intraoperative visit (treatment period): Researchers will record operation time, laser type used, surgeon's visual experience, and monitor vital signs and complications.

Postoperative visits (treatment period): Participants will be closely monitored for vital signs, symptoms, and complications within 24 hours after surgery.

Follow-up visits at 3 months and 6 months (follow-up period): Participants will undergo CT scans to assess stone clearance and recurrence.

Inclusion Criteria:

• Age ≥18 years old
• Diagnosis of kidney stones and/or upper ureteral stones with stone diameter ≥6mm and ≤20mm
• Plan to undergo fURS lithotripsy
• General anesthesia to complete the operation
• The latest urine culture before surgery is negative
• Signed and dated informed consent indicating that the patient or his or her legal representative has been fully informed about the study and has consented to participate

Exclusion Criteria:

• Isolated kidney
• Previous history of kidney transplantation or urinary diversion surgery
• Congenital malformations of urinary system
• Abnormal coagulation mechanism due to blood system diseases, liver diseases, etc.
• Severe heart or lung disease, malignancy and immune deficiency status
• Neurogenic bladder
• Failure to provide informed consent
• Have an untreated urinary tract infection
• The presence of known anatomic abnormalities (such as ureteral stenosis), urothelial tumors, or stones that can be removed directly without the use of laser lithotripsy
• Pregnant women
• In cases where the stone cannot be reached with a bendable negative pressure suction sheath, or in cases where the stone cannot be reached with a conventional sheath or the pyeloureteral junction
• Surgical completion under epidural anesthesia or lumbar anesthesia
• Recurrent stones due to genetic metabolic diseases

Patients aged 18-70 years who plan to undergo fURS lithotripsy for kidney stones and/or upper ureteral stones (6-20mm)