Kim JK et al, 2016: Clinical Nomograms to Predict Stone-Free Rates after Shock-Wave Lithotripsy: Development and Internal-Validation.
Kim JK, Ha SB, Jeon CH, Oh JJ, Cho SY, Oh SJ, Kim HH, Jeong CW.
Department of Urology, Seoul National University Hospital, Seoul, Korea.
Department of Urology, Seoul National University Bundang Hospital, Seongnam, Korea.
Department of Urology, Seoul National University Boramae Medical Center, Seoul, Korea.
PURPOSE: 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.
MATERIALS AND METHODS: 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.
RESULTS: 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.
CONCLUSIONS: 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.
PLoS One. 2016 Feb 18;11(2):e0149333. doi: 10.1371/journal.pone.0149333. eCollection 2016. FREE ARTICLE
Nomograms with the purpose of predicting stone-free rates in patients treated with SWL for stones in the kidneys and ureters, might be of some value not only for selecting the best treatment for a defined clinical problem, but also because it is one way to summarize the effects of different factors responsible for success with this treatment modality.
Kanao et al  published 2006 a simple nomogram in table-form based on the number of stones, stone diameter and location. Another approach was used by Wiesenthal et al 2011  in which stone surface area, age, BMI, stone density and stone-to-skin (STS) distance were added to the stone location. Both methods had the aim of predicting the stone-free rate after 3 months. In the latter approach curves were constructed from formulas derived separately for stones in the kidneys and ureters. In the present publication by Kim and co-workers four different nomograms are presented for patients with or without a CT-examination as well as for predicted success after one or after 2-3 SWL sessions.
In a simple attempt to evaluate and compare the messages obtained from these different nomograms I considered one renal and one ureteral stone in a 45 year old man with BMI of 27. The renal stone was located in the lower calyx and had a diameter of 15 mm, STS 100 mm and a radio-density of 650 Hounsfield units (HU). The stone in the mid ureter measured 10 mm, had a density of 800 HU, with STS 120 mm. There was no hydronephrosis. To fit into the different nomogram designs it was necessary to assume that the 15 and 10 mm stones had short diameters of 9.8 and 6.5 mm (65% of the large diameter; an average recorded in a large number of stones) The approximate surface areas were thus 115 and 51 mm2.
The very approximate predicted stone-free rates are shown in the table below:
It is obvious that the variation is considerable. It is not possible to conclude which prediction that is most accurate or reasonable. The different nomograms are based on different prerequisites, but none of them includes auxiliary procedures and in nomograms  and  re-treatments were not considered. In order to get more information the results of ureteral stone treatments previously published  were analysed with the three nomograms. The stones were located in the proximal, mid and distal ureter for which stone-free rates after one session were 73%, 67% and 83%. The auxiliary procedures in these subgroups is unknown but was theoretically estimated to about 10%.
With addition of 10-15% auxiliary procedures the different nomograms apparently give reasonably similar predictions.
Nomograms like this might be of theoretical interest, but I have difficulties to imagine the use of this device in the clinical routine. Transformation to a computerized version can possibly increase their usefulness. I find the process both complicated and time-consuming and the general impression is that no nomogram can replace personal experience. Not included in any of the nomograms are the skill of the operator, the handling of the lithotripter, anatomical features and how well the patient cooperates during the procedures.
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