The authors hypothesize that the RIRS using 150-microm Tm-fiber laser is superior than fiber with larger diameters, as 200-microm Tm-fiber laser or 200-microm holmium fiber laser, in such points as follows:

• decreasing surgery time and laser-on time due to possibility of 4.3 fold ablation efficacy increase, which has been shown by Andreeva et al.;
• increasing the flexible ureteroscope tip deflection lower pole stones availability;
• decreased risk of complications and a better irrigation and visualization due to better irrigation with smaller fiber;
• increasing of lithotripsy efficacy and laser beam density by lowering of beam focal spot due to using of lesser fiber diameter

RIRS will be performed with SP TFL or Ho:YAG (100 W). The procedure is performed under general anesthesia with the patient in the dorsal lithotomy position. The bladder is entered either with a cystoscope or a semi-rigid ureterorenoscope. Guidewires (0.035") will be used to facilitate access (under fluoroscopic guidance). After access sheath (12/14) will be placed up to the kidney pelvis. Through the access sheath ureteroscope will be introduced. For nephrolithotripsy 145 mcm and 200 mcm fibers will be used. Large fragments could be extracted with nitinol basket. After the surgery ureteral stent (7 Fr.) will be placed inside the ureter for 10 to 14 days.

A 10 Fr urethral catheter can be placed in the bladder for the drainage of the bladder during the operation.

Inclusion Criteria:

• Males and Females > 18 y.o.;
• Radiologically confirmed (CT) kidney stone;
• Stone size from 10 to 20 mm.

Exclusion Criteria:

• Multiple (more than 3) kidney stones > 5 mm