title: Calculating the number of shock waves, expulsion time, and optimum stone parameters based on noncontrast computerized tomography characteristics.
abstract: OBJECTIVE
  To define the parameters that accompanied a successful extracorporeal shock wave lithotripsy (ESWL), namely the number of shock waves (SWs), expulsion time (ET), mean stone density (MSD), and the skin-to-stone distance (SSD).
  
  
  METHODS
  A total of 368 patients diagnosed with renal calculi using noncontrast computerized tomography had their MSD, diameter, and SSD recorded. All patients were treated using a Siemens lithotripter. ESWL success meant a stone-free status or presence of residual fragments <3 mm, ET was the time in days for the successful clearance of stone fragments. Correlation was performed between the stone characteristics, number of SWs, and ET. Two multiple regression analysis models defined the number of SWs and ET. Two receiver operating characteristic curves plotted the best MSD cutoff value and optimum SSD for a successful ESWL.
  
  
  RESULTS
  Three hundred one patients were ESWL successes. A significant positive correlation was elicited between number of SWs and stone diameter, density and SSD; between ET and stone diameter and density. Multiple regressions concluded 2 equations: Number of SWs = 265.108 + 5.103 x1 + 22.39 x2 + 10.931 x3 ET (days) = -10.85 + 0.031 x1 + 2.11 x2 x1 = stone density (Hounsfield unit [HUs]), x2 = stone diameter (mm), and x3 = SSD (mm). Receiver operating characteristic curves demonstrated a cutoff value of ≤ 934 HUs with 94.4% sensitivity and 66.7% specificity and P = .0211. The SSD curve showed that a distance ≤ 99 mm was 85.7% sensitive, 87.5% specific, P <.0001.
  
  
  CONCLUSIONS
  Stone disintegration is not recommended if MSD is >934 HUs and SSD >99 mm. The required number of SWs and the expected ET can be anticipated.
authors.affiliation: Department of Urology, College of Medicine, University of Alexandria, Alexandria, Egypt. Electronic address: mkfoda@hotmail.com.
authors.forename: Khaled
authors.initials: K
authors.lastname: Foda
authors.forename: Hussein
authors.initials: H
authors.lastname: Abdeldaeim
authors.forename: Mohamed
authors.initials: M
authors.lastname: Youssif
authors.forename: Akram
authors.initials: A
authors.lastname: Assem
mesh_terms: D019540:Area Under Curve; D006801:Humans; D007669:Kidney Calculi / Q000000981:diagnostic imaging* / Q000628:therapy*; D008096:Lithotripsy / Q000379:methods*; D011446:Prospective Studies; D012372:ROC Curve; D012044:Regression Analysis; D012680:Sensitivity and Specificity; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods*; D016896:Treatment Outcome