FANS vs Standard Ureteral Access Sheath in fURS

Inclusion Criteria: 1. Participant is willing and able to provide written informed consent before any study-specific procedures are performed. 2. Male or female, aged 18 years or older. 3. Diagnosed with renal calculi ≥5 mm in diameter, confirmed by imaging, and eligible for fURS with laser lithotripsy according to European Association of Urology (EAU) guidelines. 4. In stable general health and fit for elective endoscopic surgery under general anesthesia. 5. Willing and able to comply with all study-related procedures, including follow-up imaging and clinical assessments. \- Exclusion Criteria: 1. Solitary kidney (monorenal patients). 2. Untreated positive urine culture or ongoing urinary tract infection not resolved with appropriate antibiotic therapy prior to surgery. 3. Known anatomical abnormalities of the urinary tract that may interfere with ureteroscopic access or device placement (e.g., ureteral stricture, congenital malformations). 4. Pregnancy or breastfeeding at the time of enrollment or planning pregnancy during the study period. In all female patients, a Gravindex test is performed on the day of admission; contraceptive measures are not required 5. Concomitant ureteral stone 6. Ureteral stenosis 7. Known allergy or hypersensitivity to materials used in the investigational or control ureteral access sheath. 8. Any severe comorbid condition (e.g., uncontrolled cardiovascular disease, severe coagulopathy, active malignancy) that in the opinion of the investigator would interfere with study participation or increase procedural risk. 9. Any psychological, cognitive, or social condition that may limit the ability to provide informed consent or comply with follow-up procedures.