Predicting Effectiveness of Extracorporeal Shockwave Lithotripsy by Stone Attenuation Value

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Abstract
Purpose: The aim of this study was to evaluate the effect of stone attenuation value on the effectiveness of extracorporeal shockwave lithotripsy (SWL) for upper urinary tract stones. Methods: In this prospective study, 99 patients underwent SWL for solitary renal and upper ureteral stones from January 2007 to March 2009. All patients underwent CT scan before SWL. The mean attenuation value of stones in our study was 1213.3 ± 314.5 Hounsfield units (HU). Group A consisted of 42 patients with stones of attenuation value 1200 HU. Stone size, location, requirement of number of shockwaves, shock intensities (power), retreatment rate, complication rate, auxiliary procedure rate, and effectiveness quotient (EQ) ratio were studied. Results: The mean total number of shocks required to fragment the stones in groups A and B were 1317.1 ± 345.3 and 1646.5 ± 610.8, respectively (p = 0.001), with a mean shock intensity of 12.2 ± 0.7 and 12.4 ± 0.5 kV, respectively (p = 0.03). Retreatment was not required in patients of group A, but 14.03% patients in group B required retreatment (p < 0.0001). Clearance rate in group A was 88.1%, whereas in group B it was 82.5% (p = 0.35). Auxiliary procedure rates were 9.5% and 10.5% in groups A and B (p = 0.22), respectively. EQ was 80.4% and 66.2% in groups A and B (p = 0.03), respectively. Complication rates were similar with 2.4% and 3.5% in groups A and B, respectively (p = 0.37). Significant correlation was recorded for total number and intensity of shocks with stone attenuation value. Conclusions: The EQ of SWL for upper urinary tract stones was significantly better for stones with lower attenuation value. The number and intensity of shocks required to fragment these stones with lower attenuation value were also significantly lower.

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