Factors determining stone-free rate in shock wave lithotripsy using standard focus of Storz Modulith SLX-F2 lithotripter.

OBJECTIVES: To calculate the efficiency quotient (EQ) of the latest mobile Storz Modulith SLX-F2 lithotripter and to identify the factors determining the stone-free rate.

METHODS: A retrospective review of a prospectively collected database of the first consecutive 533 patients undergoing shock wave lithotripsy (SWL) from June 2009 to February 2010 was performed. A total of 16 patients with radiolucent stones and 43 patients with incomplete follow-up were excluded. The patients were followed up with plain radiography to assess the stone-free status. Univariate and multivariate analyses were performed to identify the factors determining the stone-free rates.

RESULTS: Follow-up was complete for 474 patients, with a mean age of 54.2 ± 14.5 years. The success rate after a single SWL session was 82.7% (renal 82.2% and ureteral 83.3%; P = .81). The retreatment rate was 14.7% (renal 15.2% and ureteral 14.2%; P = .79). The stone-free rate was 77% (renal 74.1% and ureteral 80.9%; P = .10). Of the 474 patients, 43 had pre-SWL ureteral stents, and 13 required post-SWL ureteral stenting; 35 patients required post-SWL curative procedures. The EQ was 0.66, and the modified EQ was 0.62. On multivariate analysis, the stone-free patients had a smaller stone size (9.5 vs 10.3 mm, P = .02), younger age (53.1 vs 58.0 years, P = .002), right-sided stones (83.6% vs 71.0% P = .001), and the absence of a ureteral stent (78.7% vs 64.3%; P = .001).

CONCLUSIONS: The mobile Storz Modulith SLX-F2 lithotripter has an acceptable EQ of 0.66. In the present study, smaller stones (<10 mm), younger age, right-sided stones, and the absence of ureteral stents were associated with significantly greater stone-free rates.