Narrow Versus Wide Focal Zones for Shock Wave Lithotripsy of Renal Calculi

Shock wave lithotripsy (SWL) is a safe and non-invasive treatment for kidney stones. The SWL machine that is currently in use has a unique feature: the focal zone or the energy that the SWL energy is focused on in order to break kidney stones can be varied in size from a narrow (or small) focal zone to a wide (or large) focal zone. Previous lithotripters have only offered one focal size that corresponded to a narrow range. The objective of this study is to compare the single-treatment success rates of narrow and wide focal zones for the shock wave lithotripsy of renal stones between 5 and 15 mm in greatest diameter, while maintaining a constant overall lithotripsy energy level. A wide focal zone may offer some trade-offs when compared with the traditional narrow focal zone: since the area being treated is larger, it is more likely that the stone will receive adequate energy as it moves with patient breathing during treatment, and less energy per cubic inch will be delivered to the kidney around the stone (which might lead to a lower degree of renal injury); on the other hand less energy per cubic inch will also be delivered to the stone, so that stone fragmentation might be inferior to that with a narrow focal zone. Thus, with this study we want to determine whether there is a significant difference in both stone fragmentation and in renal injury (as measured by the incidence of post-treatment renal hematoma or bruises, and by measuring urinary markers indicating the degree of renal cellular damage). Aside from the random choice of focal zone size, there will be no change to the standard of care for lithotripsy treatment. We predict that the narrow focal shock zone will result in superior stone fragmentation, with higher single-treatment stone free and success rates. However, we may identify a slight increased incidence in the rate of subcapsular renal hematoma and renal damage, as detected by urinary markers.

Inclusion criteria

• Stone must be radiopaque on a KUB (kidney, ureter and bladder) radiograph, and located within the renal collecting system.
• Patients must have had a CT scan within the past 30 days.
• Stones must be solitary, between 5 and 15 mm in maximal diameter.
• Patient must consent to the trial and be willing to return to their respective lithotripsy unit at 2 weeks and 3 months for follow-up.
• Patients must be treated on the Storz Modulith SLX-F2 machine

Exclusion criteria

• More than one renal calculus on the treated side.
• Radiolucent stones (uric acid, indinavir) or cystine stones.
• Stone size < 5 mm and > 15 mm.
• Previous surgical intervention on upper tracts within past five years.
• Congenital anatomic anomalies of the kidney, ureters or bladder (such as calyceal diverticulum, horseshoe kidney, etc.)
• Patient currently taking an α-blocker (alfuzosin, terazosin, doxazosin, tamsulosin, prazosin), calcium channel blocker (verapamil, diltiazem, nifedipine, nicardipine, bepridil, mibefradil), or corticosteroids.
• Pregnancy.
• Age < 18 years.
• Active urinary tract infection.
• Patient exceed weight limit for SWL table (>500 lbs)
• Previous SWL treatment for this stone.
• Uncorrected coagulopathy