A new optical coupling control technique and application in SWL.

The objective of this study was to compare the results of shock wave lithotripsy (SWL) between patients treated with optical coupling control (OCC) and those treated with "blind" coupling during SWL to treat renal stones. Enrolled in the study were patients with urinary stones who underwent SWL between January 2014 and February 2015. The lithotripter used in the study was an electromagnetic Dornier Compact Delta II UIMS. The closed envelope method was used to randomize the enroled patients to OCC (Group A) or "Blind" coupling group (Group B). The stone-free rates (SFRs) were determined using KUB film with or without ultrasonography after 3 months. Treatment failure was defined as radiologically confirmed persistence of the stone with no fragmentation after second SWL sessions. Complications during the intraoperative or post-operative periods were recorded. A total of 336 patients satisfied the inclusion criteria for the study, of which 169 patients were treated in the Group A and 167 in the Group B. There was no significant difference in patient and stone characteristics between the two groups (Table 1). The locations of treated stones are shown in Table 2. The treatment results were stratified by stone location in Table 3, significant differences existed in all treatment results between the two groups (P < 0.05). The overall stone-free rates after 3 months were 78.2 % for kidney stones and 81.7 % for ureteral stones in patients from Group A. The corresponding SFRs for patients in Group B were 62.8 and 67.9 % for stones in the kidneys and ureters, respectively. There were statistical differences in these results between the two groups (P < 0.05). The lithotripter with OCC had excellent shock wave transmission properties with the least possible loss of energy; it can lead to the optimization of SWL treatment outcome and reduce the incidence of SW-induced adverse effects. We are confident that the OCC used in this study should be a standard feature in future lithotripters. Table 1 Patients' and stones' characteristics Group A Group B P value Number of patients 169 167 Patients' gender (M/F) 97/72 109/58 0.138 Stone location (left/right) 86/83 89/78 0.659 Patients' age (years) 36.3 ± 7.1 34.2 ± 6.8 0.521 Size of stones  Kidney (cm) 1.4 ± 0.6 1.3 ± 0.7 0.452  Ureter (cm) 1.1 ± 0.5 1.1 ± 0.4 0.354  Average size (cm) 1.2 ± 0.8 1.2 ± 0.7 0.372 Table 2 The distribution of location of stones treated Group A % Group B % Upper calyx 21 12.4 25 15.0 Middle calyx 28 16.6 23 13.8 Lower calyx 7 4.1 5 3.0 Renal pelvis 31 18.3 33 19.8 Upper ureter 28 16.6 31 18.6 Middle ureter 6 3.6 4 2.4 Lower ureter 48 28.4 46 27.5 Overall 169 100.0 167 100.0 Table 3 The treatment results were stratified by stone location Group A Group B %Stone-free %Re-treatment %Ancillary procedure %Stone-free %Re-treatment %Ancillary procedure Kidney  Upper calyx 76.2 33.3 14.3 60.0 48.0 12.0  Middle calyx 75.0 35.7 7.1 56.5 56.5 13.0  Lower calyx 71.4 42.9 28.6 60.0 60.0 40.0  Renal pelvis 83.9 29.0 9.7 69.7 45.5 12.1  Overall 78.2 33.3 11.5 62.8 50. 0 14.0 Ureter  Upper ureter 82.1 28.6 10.7 74.2 32.3 16.1  Middle ureter 66.7 66.7 33.3 50. 75.0 50.0  Lower ureter 83.3 25.0 10.4 65.0 41.3 13.0  Overall 81.7 29.3 12.2 67.9 39.5 16.0.