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Chi-Fai Ng. et al. 2024: Effect of focal zone size on treatment outcomes and renal injury following extracorporeal shockwave lithotripsy of renal calculi: a prospective randomized study

Chi-Fai Ng, Chi-Hang Yee, Jeremy Y C Teoh, Peter Ka-Fung Chiu, Angel Wy Kong, Becky Sy Lau, Chi Ho Leung, Ka-Tak Wong, Winnie Chu
Department of Surgery, SH Ho Urology Center, The Chinese University of Hong Kong, Shatin, Hong Kong.
Department of Imaging and Intervention Radiology, The Chinese University of Hong Kong, Shatin, Hong Kong

Abstract

Background: The narrower focal zone (FZ) size of modern lithotripter was considered as one of the factors that resulted in suboptimal treatment result of extracorporeal shockwave lithotripsy (SWL). Therefore, we investigate the efficacy and safety of standard narrow or extended (FZ) sizes in SWL for patients with renal stones. Materials and Methods: In this prospective study conducted between April 2018 and October 2022, patients with renal stones were randomized to receive SWL with either standard or extended FZ. Treatment was delivered using a Modulith SLX-F2 lithotripter with a maximum of 3000 shocks at 1.5 Hz. The primary outcome was treatment success 12 weeks after a single SWL session, defined as the absence of a stone or stone fragment <4 mm on computed tomography. Secondary outcomes included the incidence of perinephric hematoma, stone-free rate (SFR), and changes in the urinary levels of acute renal injury markers. Results: A total of 320 patients were recruited, and 276 patients were randomized into the two groups. The two groups had similar baseline parameters. The treatment success rate was significantly better for standard FZ (74.3%) than the extended FZ group (59.3%) (p = 0.009). Standard FZ also had a significantly better SFR (Grade-A, 36.8% vs 23.0%, p = 0.013) and less pain after treatment. Both groups had similar perinephric hematoma formation rates, unplanned hospital admission rates, and changes in urinary acute renal injury markers. Conclusions: The standard narrow FZ has better treatment efficacy and similar safety compared with the extended FZ during SWL for renal stones. This clinical trial has been registered in the public domain (CCRBCTR) under trial number CUHK_CCRB00510.

J Endourol. 2024 Mar 14. doi: 10.1089/end.2023.0662. PMID: 38482817
DOI: 10.1089/end.2023.0662

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Comments 1

Hans-Göran Tiselius on Thursday, 04 July 2024 11:00

The importance of the size of the lithotripter’s focal zone for stone disintegration has remained difficult to explain and, in the reviewer’s opinion, still is. The outstanding achievements with the Dornier HM3 lithotripter with a large focus (90 x15 mm) and relatively low energy density has not been fully understood.
A comparison of SWL with standard and large focus (28 x 6 mm and 50 x 9 mm) in Storz Modulith SLX-2, disclosed no significant difference in results in this study or in my own experience [1]. One interesting observation from my own experience is that by using the unmodified HM3, only with analgesics and sedatives, during more than 10 years, clinically symptomatic renal hematomas were never encountered. A hematoma was not diagnosed until a small focus/ high energy lithotripter was used.
Undoubtedly, a lithotripter with small focus and high pressure has the capacity to successfully disintegrate stones, at least if the stone size is not too large. A limited increased focal zone as used in this study obviously had no significant influence on stone disintegration, at least when electromagnetic shock wave generation is used.
Why the “performance of new lithotripters has never reached that of HM3” so far remains unexplained.
Experimental studies with Eisenmengers wide-focus (180 x 18 mm) and low pressure ESWL device showed good fragmentation properties with stone-free rates of 86-97%. [2] The large focus and the low energy density favor fragmentation with squeezing. Conclusions on the importance of the focus geometry relative to stone size today is hampered by the adaptation of guidelines to how people select patients and normally use SWL.
In my own old experience with the Dornier HM3 device successful disintegration was possible to obtain with cystine, brushite and COM-stones. For some of these successfully disintegrated and relatively large stones, I would not anticipate a similar outcome with a small focus lithotripter despite much higher energy density.
So, in summary small variations in focus volumes obviously had no significant effect on disintegration of stones measuring 5-15 mm.
Given the popularity of endourology among young urologists I understand that there is little or no interest in developing lithotripters with the possibility to use a much wider focus with reduced energy density than that encountered in modern lithotripters, but it would indeed be highly interesting…
References
1. Tiselius HG. How efficient is extracorporeal shockwave lithotripsy with modern lithotripters for removal of ureteral stones?
.J Endourol. 2008 Feb;22(2):249-55.

2. Eisenmenger W, Du XX, Tang C, Zhao S, Wang Y, Rong F, Dai D, Guan M, Qi A.The first clinical results of "wide-focus and low-pressure" ESWL. Ultrasound Med Biol. 2002 Jun;28(6):769-74.

Hans-Göran Tiselius

The importance of the size of the lithotripter’s focal zone for stone disintegration has remained difficult to explain and, in the reviewer’s opinion, still is. The outstanding achievements with the Dornier HM3 lithotripter with a large focus (90 x15 mm) and relatively low energy density has not been fully understood. A comparison of SWL with standard and large focus (28 x 6 mm and 50 x 9 mm) in Storz Modulith SLX-2, disclosed no significant difference in results in this study or in my own experience [1]. One interesting observation from my own experience is that by using the unmodified HM3, only with analgesics and sedatives, during more than 10 years, clinically symptomatic renal hematomas were never encountered. A hematoma was not diagnosed until a small focus/ high energy lithotripter was used. Undoubtedly, a lithotripter with small focus and high pressure has the capacity to successfully disintegrate stones, at least if the stone size is not too large. A limited increased focal zone as used in this study obviously had no significant influence on stone disintegration, at least when electromagnetic shock wave generation is used. Why the “performance of new lithotripters has never reached that of HM3” so far remains unexplained. Experimental studies with Eisenmengers wide-focus (180 x 18 mm) and low pressure ESWL device showed good fragmentation properties with stone-free rates of 86-97%. [2] The large focus and the low energy density favor fragmentation with squeezing. Conclusions on the importance of the focus geometry relative to stone size today is hampered by the adaptation of guidelines to how people select patients and normally use SWL. In my own old experience with the Dornier HM3 device successful disintegration was possible to obtain with cystine, brushite and COM-stones. For some of these successfully disintegrated and relatively large stones, I would not anticipate a similar outcome with a small focus lithotripter despite much higher energy density. So, in summary small variations in focus volumes obviously had no significant effect on disintegration of stones measuring 5-15 mm. Given the popularity of endourology among young urologists I understand that there is little or no interest in developing lithotripters with the possibility to use a much wider focus with reduced energy density than that encountered in modern lithotripters, but it would indeed be highly interesting… References 1. Tiselius HG. How efficient is extracorporeal shockwave lithotripsy with modern lithotripters for removal of ureteral stones? .J Endourol. 2008 Feb;22(2):249-55. 2. Eisenmenger W, Du XX, Tang C, Zhao S, Wang Y, Rong F, Dai D, Guan M, Qi A.The first clinical results of "wide-focus and low-pressure" ESWL. Ultrasound Med Biol. 2002 Jun;28(6):769-74. Hans-Göran Tiselius
Thursday, 13 February 2025