Introduction: To evaluate stone free rate (SFR) with low dose computed tomography-Kidney Ureter Bladder (CT-KUB) after retrograde intrarenal surgery (RIRS) and compare the relation of stone clearance with stone volume and Hounsfield Unit (HU).

Materials and Methods: The prospective observational study was conducted in Bir Hospital from January 2019 to January 2020 . A total of 42 patient with renal stone up to 20 mm size included. Lithotripsy was performed using Holmium laser utilizing High frequency Low Power Energy (HiFrLoPE). Stone clearance was reassessed using low dose CT KUB at 1 month who were stone free on X-ray and ultrasound scan at 2 weeks. Patients were categorized as complete stone free, clinically insignificant Residual Fragment (CIRF) <4 mm and CIRF > 4 mm.

Results: The mean stone volume and HU were 553.37±338.10 and 1063.5±378.07 respectively. Complete SFR was 59% and 35.7% with stone volume <500 and 500-1000 mm3 (P<0.05) respectively. Similarly, Complete SFR was 66.67% and 33.34% with HU<500 and >1500 (P<0.05) respectively. We achieved complete stone clearance in 18 patients (42.85%), whereas 16 patients (38.09%) had CIRF < 4mm and 8 patients (19.04%) had CIRF > 4mm.Low dose CT KUB detected stones in 57.25% patients who were considered stone free based on X-ray and USG KUB findings.

Conclusion: SFR in RIRS is high for renal stones with lower stone volume and low HU. Low dose CT KUB allows more accurate detection of residual fragments than X-ray and USG KUB during follow up of patients after RIRS.


Keywords: Computed Tomography, scope, Kidney Stone, Holmium Laser