Impact of focal zone size on treatment outcomes and renal injury subsequent to extracorporeal shockwave lithotripsy for renal calculi

A recent study showed that the standard narrow focal zone (FZ) demonstrates similar safety and superior treatment efficacy when compared to the extended FZ during extracorporeal shockwave lithotripsy (SWL) for renal stones. This study’s findings were published in Journal of Endourology.

In this prospective randomized study, 276 patients diagnosed with renal stones were assigned to receive SWL using either standard or extended FZ. The treatment was administered using a Modulith SLX-F2 lithotripter, delivering a maximum of 3000 shocks at a frequency of 1.5 Hz. The primary outcome of the study assessed the success of the treatment 12 weeks after a single SWL session, which was determined by the absence of a stone or stone fragment smaller than 4 mm on computed tomography. Secondary outcomes included the incidence of the stone-free rate (SFR), perinephric hematoma, and changes in the levels of acute renal injury markers in the urine.

Similar baseline parameters were observed in both groups. The standard FZ group achieved a significantly higher treatment success rate (74.3%) than the extended FZ group (59.3%). Additionally, standard FZ exhibited a significantly better SFR (Grade-A, 36.8% vs. 23.0%,) and lower post-treatment pain levels. Both groups had comparable rates of perinephric hematoma formation, changes in urinary acute renal injury markers, and unplanned hospital admissions.

The above results demonstrated that the standard narrow FZ shows comparable safety and improved treatment efficacy in comparison to the extended FZ in extracorporeal SWL for renal stones.