Clinical Nomograms to Predict Stone-Free Rates after Shock-Wave Lithotripsy: Development and Internal-Validation

<div><p>Purpose</p><p>Shock-wave lithotripsy (SWL) is accepted as the first line treatment modality for uncomplicated upper urinary tract stones; however, validated prediction models with regards to stone-free rates (SFRs) are still needed. We aimed to develop nomograms predicting SFRs after the first and within the third session of SWL. Computed tomography (CT) information was also modeled for constructing nomograms.</p><p>Materials and Methods</p><p>From March 2006 to December 2013, 3028 patients were treated with SWL for ureter and renal stones at our three tertiary institutions. Four cohorts were constructed: Total-development, Total-validation, CT-development, and CT-validation cohorts. The nomograms were developed using multivariate logistic regression models with selected significant variables in a univariate logistic regression model. A C-index was used to assess the discrimination accuracy of nomograms and calibration plots were used to analyze the consistency of prediction.</p><p>Results</p><p>The SFR, after the first and within the third session, was 48.3% and 68.8%, respectively. Significant variables were sex, stone location, stone number, and maximal stone diameter in the Total-development cohort, and mean Hounsfield unit (HU) and grade of hydronephrosis (HN) were additional parameters in the CT-development cohort. The C-indices were 0.712 and 0.723 for after the first and within the third session of SWL in the Total-development cohort, and 0.755 and 0.756, in the CT-development cohort, respectively. The calibration plots showed good correspondences.</p><p>Conclusions</p><p>We constructed and validated nomograms to predict SFR after SWL. To the best of our knowledge, these are the first graphical nomograms to be modeled with CT information. These may be useful for patient counseling and treatment decision-making.</p></div

Baseline characteristics of the total cohort and each development cohort.

<p>Baseline characteristics of the total cohort and each development cohort.</p

Calibration plots for nomograms predicting stone-free rates after the first and within the third session of SWL with and without CT information.

<p>(A) Total-development cohort, (B) CT-development cohort.</p

Study flowchart for patient selection.

<p>Study flowchart for patient selection.</p

The concordance index (c-index) yielded by AUC to evaluate the predictive discrimination of the nomograms.

<p>The concordance index (c-index) yielded by AUC to evaluate the predictive discrimination of the nomograms.</p

Multivariate logistic regression models in the development cohorts.

<p>Panel A represents stone-free after the first session of Shock-wave lithotripsy (SWL) and panel B shows stone-free within the third session of SWL.</p