Method for predicting effectiveness of extracorporeal shock wave lithotripsy of solitary kidney stones

Abstract

FIELD: urology; radiation diagnostics.SUBSTANCE: used to predict the effectiveness of extracorporeal shock wave lithotripsy (ESWL) of single renal stones smaller than 20 mm. Based on the data of multispiral computed tomography (MSCT), the size of the calculus in the axial, frontal and sagittal planes is determined, and the volume of the calculus is calculated using the maximum values obtained using the triaxial ellipsoid formula. Using the bone density window, the zone of maximum density of the calculus is determined in all planes by selecting the area of interest in such a way that the value of the standard deviation from the average in this area does not exceed 50±5 HU. The dimensions of the maximum density zone are measured in the specified planes and, taking into account the maximum values obtained, the volume of the maximum density zone is calculated using the triaxial ellipsoid formula. The ratio of the volume of the zone of maximum density to the volume of the calculus is determined as a percentage, and if its value is 5% or less, the effectiveness of ESWL is predicted.EFFECT: method ensures increased accuracy and objectivity of preoperative prediction of the effectiveness of ESWL due to a three-dimensional assessment of the spatial structure and volume of the densest part of the calculus, which ensures a personalized choice of treatment tactics and eliminates obviously ineffective interventions.1 cl, 2 dwg, 2 tbl, 2 ex

Description

[0001] The invention relates to medicine, in particular to urology, and can be used in clinical practice to predict the effectiveness of remote shock wave lithotripsy of single renal stones less than 20 mm in size in patients with nephrolithiasis.

[0002] Extracorporeal shock wave lithotripsy (ESWL) is one of the surgical treatment options for patients with urolithiasis and intrarenal stones ranging in size from 10 to 20 mm. The leading criterion for the effectiveness of ESWL is the complete destruction of the stone after a lithotripsy session to fragments smaller than 4 mm, verified by radiographic imaging methods 3 months after surgery [Khasigov A.V., Khazhokov M.A., Ilyash A.V., Glukhov V.P., Naboka Yu.L., Gudima I.A. Efficiency and safety of extracorporeal shock wave lithotripsy of simple renal pelvic stones. Bulletin of urology. 2017; 5 (3): 39-48]. The predictive factors for the success of the chosen treatment method include the individual anatomical and physiological characteristics of the patient and the characteristics of the calculus.Multispiral computed tomography of the retroperitoneal space (MSCT RP) is the “gold standard” for diagnosing nephrolithiasis. It allows one to determine the location, size, area, minimum, average and maximum density (in Hounsfield units, HU) of the stone at the preoperative stage, assess the anatomy of the renal collecting system and the condition of the underlying urinary tract, and measure the distance from the skin to the stone.

[0003] Today, in addition to the maximum calculus size (less than 20 mm), MSCT parameters such as the average calculus density (less than 1000 HU) and the distance from the skin to the stone (less than 100 mm) are widely used in clinical practice to predict the effectiveness of extracorporeal shock wave lithotripsy of nephroliths [Zeng G., Zhong W., Chaussy CG, et al. International Alliance of Urolithiasis Guideline on Shockwave Lithotripsy. Eur Urol Focus. 2023;9(3):513-523]. In recent years, a number of domestic and foreign publications have been aimed at finding additional MSCT factors for predicting the success of an ESWL session. It is important to understand that the largest diameter refers to a two-dimensional dimension and cannot fully describe the actual size of a stone, which is a stereoscopic figure. The prognostic significance of calculating the stone volume as a predictor of a successful outcome of a ESWL session is substantiated.In an analysis of 312 patients undergoing extracorporeal shock wave lithotripsy, the authors found a significant relationship between complete stone disintegration in one crushing session and its volume (p < 0.001) [Langenauer J., Betschart P., Hechelhammer L., et al. Advanced non-contrasted computed tomography post-processing by CT-Calculometry (CT-CM) outperforms established predictors for the outcome of shock wave lithotripsy. World J Urol. 2018 Dec;36(12):2073-2080]. Similarly, another study demonstrated that lithovolume determination is a significant predictor of effective stone elimination by ESWL (p < 0.001) [Bandi G., Meiners RJ, Pickhardt PJ, et al. Stone Measurement by Volumetric Three-dimensional Computed Tomography for Predicting the Outcome After Extracorporeal Shock Wave Lithotripsy. BJU Int. 2009;103(4):524-8].The authors of the following study demonstrated a statistically significant prevalence of the influence of calculating the stone volume on the success of lithotripsy compared to determining its two-dimensional characteristics (maximum size and area) [Cui HW, Tan TK, Christiansen EE, et al. The Utility of Automated Volume Analysis of Renal Stones Before and After Shockwave Lithotripsy Treatment. Urolithiasis. 2021;49(3): 219-226].

[0004] At the same time, an analysis of numerous publications indicates great interest in the depsitometric CT parameters of the stone and their interpretation as a prognostic factor for the upcoming effective elimination. The closest to the proposed invention is the method for determining the prognosis of the results of extracorporeal shock wave lithotripsy based on computed tomography scanning data, proposed by Bobylev D.A. et al. (patent for invention No.: 2737335, 01.06.2018). The predictive ability of this method was based on calculating the ratio of the average area of ​​​​high homogeneity to the average area of ​​​​the calculus. This method involves assessing the two-dimensional characteristics of the nephrolith (the area of ​​​​the stone and the area of ​​​​the zone of its maximum density) and does not take into account its three-dimensional geometric shape, which reduces the prognostic accuracy.

[0005] The objective of the proposed invention is to develop a method for predicting the effectiveness of extracorporeal shock wave lithotripsy of solitary kidney stones, taking into account their stereoscopic characteristics. This will allow for a personalized approach and selection of the most effective treatment method, while reducing the number of unsuccessful procedures. The method consists of the following: in accordance with clinical recommendations, the patient undergoes a native computed tomography scan before a ESWL session. The stone size is assessed in three mutually perpendicular planes, and the maximum values ​​obtained are recorded. The stone volume is calculated using the triaxial ellipsoid formula recommended by the European Association of Urologists: l * a * b * c * 0.167, where a is the length, b is the width, and c is the height.Using the bone density window, the zone of maximum density is determined in all planes by defining a region of interest (ROI) such that the standard deviation (SD) from the mean in this area does not exceed 50±5 HU, indicating high densitometric homogeneity of this zone. The dimensions of the zone of maximum density are then measured in three mutually perpendicular planes. Taking into account the largest obtained values, the volume of the zone of maximum density is calculated using the triaxial ellipsoid formula described above. The percentage ratio of the volume of the zone of maximum density to the volume of the nephrolith is considered a volumetric indicator predicting the success of lithotripsy. If this indicator is 5% or less, then disintegration and complete passage of the nephrolith are highly likely to occur after a single fragmentation session.If the volumetric index is more than 5%, then one session of ESWL will be ineffective and the patient should consider alternative surgical options for removing the stone from the renal pelvis and calyces: percutaneous nephrolithotripsy with lithoextraction or transurethral nephrolithotripsy.

[0006] The study involved 112 patients who underwent extracorporeal shock wave lithotripsy between September 1, 2024, and August 6, 2025, in the Urology Departments No. 1, No. 2, and No. 3 of the S. R. Mirotvortsev University Clinical Hospital No. 1, V. I. Razumovsky Saratov State Medical University of the Ministry of Health of the Russian Federation. The patients' ages ranged from 20 to 74 years, including 60 (53.6%) men and 52 (46.4%) women.

[0007] In order to evaluate the effectiveness of the ESWL session, all patients underwent multispiral computed tomography of the retroperitoneal organs 3 months after the operation.

[0008] The inclusion criteria for the study were: the presence of urolithiasis confirmed by the results of preoperative MSCT of the RP, age over 20 years and < 75 years, the presence of a single renal stone measuring 10 to 20 mm. The exclusion criteria were: extrarenal stones, multiple nephroliths, active infection at any location, decompensated comorbidity. Multispiral computed tomography of the retroperitoneal space in native mode was performed on a single-energy CT Optima 540 system (GE Healthcare). At the preoperative stage, the following nephrolith characteristics were assessed: location, average density (HU), stone size (in three mutually perpendicular planes), size of the zone of maximum density, lithovolume, and volume of the zone of maximum density.

[0009] Extracorporeal shock wave lithotripsy was performed using a Sonolith i-sys (EDAP TMS) extracorporeal lithotripter. The number of pulses delivered per session ranged from 2,000 to 4,000, and the generator power ranged from 12.5 to 16.5 kV.

[0010] The statistical parameters were calculated using the TIBCO® Statistica 14.0.0.15 software package. Statistical estimates of the studied parameters are presented as the median (Me) ± standard deviation (o). The normality of the distribution of values ​​was tested using the Kolmogorov-Smirnov test. Since the distribution in the sample differed from normal, nonparametric statistics methods (Spearman's R-test) were used to assess the presence and strength of the correlation between the volume indicator and the effectiveness of the ESWL procedure. Differences were considered reliable at a significance level of p < 0.01. ROC (receiver operator characteristic) analysis was used to determine the sensitivity and specificity of the studied parameters. The information content was assessed by the AUC (area under curve) value.

[0011] All examined patients were divided into two groups matched for gender and age. The first group included patients (n=57) whose treatment strategy was based on standard MSCT stone characteristics—maximum size and average stone density (HU). The second group consisted of patients (n=55) for whom indications for ESWL were determined based on the volumetric indicator, predicting its effectiveness. In both groups, patients were divided into two subgroups based on the number of sessions required for complete elimination of the nephrolith: subgroup I—patients who required one ESWL session; subgroup II—patients who underwent two or more ESWL sessions. Complete disintegration of the stone as a result of one session was considered effective lithotripsy.

[0012] The relationship between the number of ESWL sessions and the localization of stones in the renal cavitary system in patients with nephrolithiasis is presented in Table 1.

[0013] Localization of stones Number of patients treated with ESWL

[0014] First group (n=57) Second group (n=55) Subgroup I Subgroup II Subgroup I Subgroup II Abs. % Abs. % Abs. % Abs. % Pelvis 18 1,6 12 21,05 18 32,7 9 16,4 Upper group of cups 3 5,3 1 1,75 7 12,7 0 0 Middle group of cups 6 10,5 5 8,8 8 14,6 2 3,6 Lower group of cups 8 14,0 4 7,0 9 16,4 2 3,6 Total 35 61,4 22 38,6 42 76,4 13 23,6

[0015] MSCT characteristics of renal stones are shown in Table 2.

[0016] Stone parameter Number of patients treated with ESWL First group Second group Subgroup I Subgroup II Subgroup I Subgroup II Maximum size (mm), Me±o 13,7000 ± 1,5522 12,3000±1,5927 13,6500±0,9617 13,1000± 1,5925 Average density of pephrolite (HU), Me±o 701,0000±152,0243 750,0000±99,0078 678,0000±149,4986 679,0000±110,7599 Volumetric index (%), Me±o 1,6548 ± 1,2359 5,4994±3,8731 2,2231±1,4159 5,5952 ±2,2062

[0017] In a retrospective analysis of the results of postoperative CT studies of patients, the volumetric indicator in the first subgroup was 1.6548 ± 1.2359 (%), and in the second - 5.4994 ± 3.8731 (%). The results of the ROC analysis demonstrated high sensitivity and specificity of this parameter: the area under the ROC curve, corresponding to the relationship between the prognosis of effective nephrolith elimination after 1 session of ESWL and the volumetric indicator, was 0.877 ± 0.0499 (95% CI: from 0.763 to 0.949). The correlation analysis of the obtained data when determining the Spearman R-criterion revealed statistically significant relationships between the measured indicators. An inverse, reliable and significant (p=0.6442, at p<0.0001, 95% CI: from 0.7747 to -0.4610) relationship was found between the volume indicator and the probability that one session of extracorporeal shock wave lithotripsy would be required for the successful removal of a renal calculus.

[0018] For patients in the second group, the extracorporeal shock wave lithotripsy procedure was prescribed based on the volumetric indicator. If the volumetric indicator was 5% or less, ESWL was used; if it was greater than 5%, percutaneous nephrolithotripsy with lithoextraction or transurethral nephrolithotripsy was performed. In the first group, the number of patients who required only one extracorporeal shock wave lithotripsy session to successfully remove stones was 35 (61.4%), while in the second group, the number was 42 (76.4%). Thus, taking our proposed indicator into account when planning patient management tactics increased the rate of successful lithotripsy by 15%.

[0019] The method is illustrated with clinical examples.

[0020] Example 1.

[0021] Patient F., 63 years old. According to the MSCT of the left kidney, a calculus was found in the middle calyx of the left kidney, measuring 6.8 x 4.7 x 10.9 mm, with an average density of 519 HU. The volume of the stone was 182.7 mm 3. Fig. 1 shows a MSCT image of the calculus (bone density window, Perfusion type visualization), where the zone of maximum density (1) and its maximum dimensions (2) are marked in the axial (2.5 mm) (Fig. 1a), frontal (3.1 mm) (Fig. 1b) and sagittal (2.4 mm) (Fig. 1c) projections. The volume of the zone of maximum density was 6.5 mm 3 When calculating the volumetric indicator, its value was 3.6%, which suggested effective elimination of the nephrolith after the lithotripsy session. Postoperatively, the patient reported spontaneous passage of stone fragments. Results of a CT scan of the renal pelvis three months after ESWL confirmed complete clearance of the stone and its fragments from the renal pelvic cavity.

[0022] Example 2.

[0023] Patient G., 32 years old. According to the MSCT of the right renal pelvis, a calculus was detected in the right renal pelvis, measuring 8.7 x 9.8 x 10.3 mm, with an average density of 825 HU. The volume of the stone was 460.5 mm 3. Fig. 2 shows a MSCT image of the calculus (bone density window, Perfusion type visualization), where the zone of maximum density (1) and its maximum dimensions (2) are marked in the axial (5.4 mm) (Fig. 2a), frontal (3.1 mm) (Fig. 2b) and sagittal (3.1 mm) (Fig. 2c) projections. The volume of the zone of maximum density was 40.4 mm 3 The volumetric indicator was 8.8%, which is inconsistent with the expected effective elimination of the nephrolith in a single ESWL session. Based on the obtained data, percutaneous nephrolithotripsy with lithoextraction was recommended according to the proposed prognostic method, but the patient declined. After a single shock wave session, complete disintegration of the stone was not achieved, requiring another ESWL session.

Claims

A method for predicting the effectiveness of extracorporeal shock wave lithotripsy (ESWL) for solitary renal calculi smaller than 20 mm, including measuring the size of the calculus and the zone of its maximum density using multispiral computed tomography (MSCT) data, characterized in that the size of the calculus in the axial, frontal and sagittal planes is determined using MSCT data and the volume of the calculus is calculated using the maximum values ​​obtained using the triaxial ellipsoid formula;using the bone density window, the zone of maximum density of the calculus is determined in all planes by selecting the area of ​​interest in such a way that the value of the standard deviation from the average in this area does not exceed 50±5 HU, then the dimensions of the zone of maximum density are measured in the specified planes and, taking into account the maximum values ​​obtained, the volume of the zone of maximum density is calculated using the triaxial ellipsoid formula, then the ratio of the volume of the zone of maximum density to the volume of the calculus is determined as a percentage and, if its value is 5% or less, the effectiveness of ESWL is predicted.

Images