Defining The Learning Curve of Flexible Ureterorenoscopy and Laser Lithotripsy Cem Kezer1, Faruk Ozgor2* Purpose: To investigate the impact of learning curve (LC) on flexible ureterorenoscopy (f-URS). Materials and Methods: Patients who underwent kidney stone surgery in a urology clinic from a tertiary health care institution with f-URS were enrolled in the study. Patient characteristics, the properties of kidney and kidney stones were recorded. Also, f-URS-related parameters, hospitalization time, the success of the procedure, and complications were noted. Patients were categorized equally into 4 groups, the first 20 f-URS cases in Group 1, and the last 20 f-URS cases in Group 4. Groups were compared according to patient preoperative parameters, in- traoperative outcomes, success rate and complication rate. Results: Time from the induction of anaesthesia to insertion of flexible ureterorenoscope was 18.6 min in group 1 and 17.2 min in group 2; then it significantly decreased to 15.0 min for cases 40 through 60 and 12.4 min for cases 60 through 80 (p = 0.001). Operation time in group 3 and group 4 was significantly shorter than in group 1 and group 2 (p = 0.001). Also, fluoroscopy time was significantly longer in group 1 (82.9 seconds) and reached a plateau in group 3 (50.3 seconds) and group 4 (41.7 seconds) (p = 0.001). Additionally, after the 20th case, we achieved a significantly higher success rate in comparison to the first 20 cases (65% in group 1, 85% in group 2, 85% in group 3, and 90% in group 4, p = 0.001). Conclusion: Flexible ureterorenoscopy is a surgery that requires high technique and experience. The present study found that success of f-URS reached satisfactory levels after 20th cases. In addition, 40 cases may be enough for surgical proficiency regarding decreases in preparation time, operation time, and fluoroscopy time. Keywords: flexible ureterorenoscopy; learning curve; lithotripsy; success INTRODUCTION Flexible ureterorenoscopy (f-URS) is an endoscopic surgery which is used in diagnosis and treatment of pathologies of the upper urinary system. Although f-URS can be used for cancers and obstructions of the upper urinary tract, the main indication for f-URS is kidney stones(1). According to European Urology As- sociation Urolithiasis guidelines, f-URS is the preferred surgical method for kidney stones smaller than 20 mm, achieving higher stone free status compared to Shock Wave Lithotripsy and associated with lower complica- tion rates compared to percutaneous nephrolithotomy (PNL)(2). Stone size, possible stone composition, anat- omy of the kidney, clinician and patient preference are important factors in the choice of treatment(3). Percuta- neous nephrolithotomy is the gold standard treatment for kidney stones larger than 2 cm(4). For stones between 1-2 cm, all modalities may be appropriate, but the suc- cess of SWL seems to be low for kidney lower pole stones(3). The learning curve (LC) is defined as the period and/ or number of operations an average surgeon requires in order to perform an operation with acceptable suc- cess and complication rates according to the literature(4). Previous studies investigated the LC of different surgi- cal procedures and studies stated that different surgical 1Department of Urology, Erdem Hospital, Istanbul, Turkey. 2Department of Urology, Haseki Training and Research Hospital, Istanbul, Turkey. *Correspondence: Haseki Training and Research Hospital, Millet Street, Istanbul, Turkey. Tel: +90 536 728 63 12. Fax: +90 212 585 44 00. E-mail: md.farukozgor@gmail.com Received August 2022 & Accepted November 2022 procedures have unique learning curves. Sahan and col- leagues investigated the LC for supine mini PNL, and emphasized that surgeons achieved satisfactory success rate and complication rate after 45 mini PNL cases(6). In another study about LC in robotic-assisted laparoscop- ic retroperitoneal lymph node dissection, Sophia et al. found significant decreases in complications and opera- tion time after 44 cases(7). Although previous reports analysed the LC of different stone surgery methods, no study has evaluated the LC for f-URS. This study is the first prospective research to investigate to LC for f-URS. MATERIALS AND METHODS The present study was planned according to the princi- ples of the Helsinki Declaration from July 2017 to July 2020. Patients who underwent kidney stone surgery with f-URS were enrolled in the study. Eighty patients were included in the study. All f-URS operations were done by one surgeon, who had experience of 250 ure- terorenoscopy and 100 PNL cases. Also, the surgeon observed 100 f-URS cases and participated in a 12-hour f-URS course including a simulation programme and dry laboratory. Patients with kidney stone ≤ 20 mm were accepted as candidates for f-URS. Patients with renal abnormalities, and with history of coagulopathy Urology Journal/Vol 20 No. 1/ January-February 2023/ pp. 7-10. [DOI: 10.22037/uj.v19i.7389] ENDOUROLOGY AND STONE DISEASE were excluded from the study. Also, bilateral f-URS cases, patients < 18 years of age, patients with history of ureteral stenosis, and patients with positive urine cul- ture operated under antibiotic regimen were excluded. Patient characteristics and operative parameters were noted. F-URS-related parameters, hospitalization time, complications, and success were recorded. Patients were categorized into four groups, as the first 20 f-URS cases in Group 1, and the last 20 f-URS cases in Group 4. Groups were compared in regards of patient preoper- ative data, operative parameters, success rate, and com- plication rate. Surgical technique Under general anesthesia, a safety guide wire was in- serted into renal pelvis. After, ureterorenoscopy was performed for direct visualisation of the ureter and pas- sive dilatation of the ureter to facilitate insertion of the ureteral access sheath (11-13 Fr diameter). Fibre optic f-URS (Storz FLEX-X2, Tuttlingen, Germany) was used and stone fragmentation was done with 200 or 273 μm laser fibre. Stone retrieval was performed with niti- nol baskets. At the end of the operation, 4.8 F JJ stent was inserted under fluoroscopy guidance. The presence of any residual stone was evaluated by kidney-ureter-bladder (KUB) graphy on the first day after the operation. Final stone free status was assessed with non-contrast abdominal computed tomography in the third postoperative month. Success was accepted as the absence of any stone. Statistical analysis Study sample size analysis was computed using the G*Power (Erdfelder, Faul, & Buchner, 1996) program. The study of Jang et al. was used as a pilot study to cal- culate the sample size(8). To obtain a significance of α = 0.05, and 90% power (1-β = 0.9), the required sample size per group was at least 16. Statistical analysis was done by using Statistical Package for the Social Sciences version 20 (SPSS IBM Corp., Armonk, NY, USA). The distribution of continuous variables was determined by Shapiro–Wilk test. One-way ANOVA test was used for the comparison of continuous variables. Levene’s test was performed to evaluate the homogeneity of variance. Tukey test and Games-Howell test were used for post hoc analysis to compute pairwise comparisons. For categorical variables, Chi Square test was used for binary outcomes with large expected cell counts and Fisher ́s exact test for small cell counts. The data were analysed at 95% confidence level and P value of less than 0.05 was accepted as statistically significant. RESULTS Total 80 participants were divided into four groups and 14 patients were excluded (eight patients had JJ stent, one patient had nephrostomy tube, two patients under- went bilateral f-URS operation, one patient had pelvic kidney, one patient was operated under antibiotic reg- imen and one patient was under 18 years of age). The mean age of participants was 44.6 ± 14.6 years, and 52 (65%) patients were male. The most common stone lo- Learning Curve of Flexible Ureterorenoscopy-Kezer et al. Endourology and Stones diseases 8 Group 1 (n=20) Group 2 (n=20) Group 3 (n=20) Group 4 (n=20) P value Age (years)* 47.6 ± 13.8 46.7 ± 15.6 41.3 ± 13.6 42.6 ± 15.6 0.359 Sex 0.988 Male 12 (60%) 13 (65%) 14 (70%) 13 (65%) Female 8 (40%) 7 (35%) 6 (30%) 7 (35%) BMI (kg/m²)* 28.3 ± 5.0 27.7 ± 5.5 27.1 ± 5.4 29.0 ± 5.3 0.692 ASA score 0.920 ASA 1 15 (75%) 13 (65%) 15 (75%) 15 (75%) ASA 2-3 5 (25%) 7 (35%) 5 (25%) 5 (25%) History of previous stone surgery 4 (20%) 7 (35%) 3 (15%) 5 (25%) 0.565 Stone opacity (non-opaque) 2 (10%) 1 (5%) 3 (15%) 0 (0%) 0.499 Stone localization 0.365 Upper 10 (50%) 6 (30%) 9 (45%) 6 (30%) Pelvis 5 (25%) 9 (45%) 5 (25%) 9 (45%) Lower 3 (15%) 2 (10%) 4 (20%) 2 (10%) Multiple 2 (10%) 3 (15%) 2 (10%) 3 (15%) Stone size (mm)* 12.8±4.4 11.8 ± 3.9 12.7 ± 3.6 12.6 ± 3.7 0.683 Presence of hydronephrosis 12 (60%) 8 (40%) 10 (50%) 8 (40%) 0.576 Operation side 0.872 Right 13 (65%) 10 (50%) 11 (55%) 12 (60%) Left 7 (35%) 10 (50%) 9 (45%) 8 (40%) Table 2. Comparison of preoperative demographic data between groups *mean ± standard deviation BMI: Body mass index, ASA: American society of anesthesiologists Table 1. Demographic and postoperative data of all patients. N = 80 Age (years)* 44.6 ± 14.6 Sex Male 52 (65%) Female 28 BMI (kg/m²)* 28.0 ± 5.2 ASA score ASA 1 58 (72.5%) ASA 2-3 22 History of previous stone surgery 19 (23.7%) Stone opacity (non-opaque) 6 (7.5%) Stone localization Upper 31 (38.7%) Pelvis 28 (35.0%) Lower 11 (13.8%) Multiple 10 (12.5%) Stone size (mm)* 12.5 ± 3.8 Presence of hydronephrosis 38 (47.5%) Operation side Right 46 (57.5%) Left 34 Success 65 (81.2%) Complications 6 (7.5%) Minor (Clavien-Dindo grade 1-2) 5 (6.3%) Major (Clavien-Dindo grade 3-5) 1 *mean ± standard deviation BMI: Body mass index, ASA: American society of anesthesiologists cation was upper calyx (31 patients, 38.7%), and ten patients had multiple renal stones. The mean stone size was 12.5 mm. Overall success was 81.2% and compli- cations occurred in six (7.5%) patients (Table 1). Age, sex, BMI, and ASA score were comparable be- tween all groups. Also, operation side, stone size, stone location and stone opacity were not statically signifi- cant. Comparison of pre-surgical parameters is summa- rized in Table 2. Time from the induction of anaesthesia to insertion of flexible ureterorenoscope was 18.6 min in group 1 and 17.2 min in group 2; then it decreased to 15.0 min for cases 40 through 60 and 12.4 min for cases 60 through 80 (p = 0.001). Similarly, operation time progressive- ly decreased (44.1 min, 38.7 min, 33.0 min, and 30.0, respectively) and operation time in group 3 and group 4 was significantly shorter (p = 0.001). Also, fluoros- copy time was significantly longer in group 1 (82.9 ± 15.0 seconds) and reached a plateau in group 3 (50.3 ± 14.4 seconds) and group 4 (41.7 ± 16.4 seconds) (p = 0.001). Additionally, after the 20th case, we achieved a significantly better success rate (65% in group 1, 85% in group 2, 85% in group 3, and 90% in group 4, p = 0.001). Hospitalization time and complication rate were similar between the groups (p = 0.581 and p = 0.712) (Table 3). DISCUSSION The learning curve is an entity to define the number of operations that a surgeon should do before reaching pro- ficiency level. Previous reports attempted to determine the LC for different procedures in urology practice(9,10), but no study evaluated the LC for f-URS yet. This study focused to determine LC of f-URS for the first time. Our results showed that the success of f-URS reached a plateau after 20 cases. In addition, preparation time, operation time, and fluoroscopy duration were signifi- cantly decreased following 40 cases. The mean goal of kidney stone surgeries is to obtain stone free status without complications. Stone-free rate following f-URS was reported to have a wide range, be- tween 50% and 100% (11). Although no study focused on the impact of LC on f-URS success, Ziaee and col- leagues investigated the number of cases required to complete the LC following PNL, and obtained suffi- cient stone free rates after 105 PNL operations(7). Sahan et al. achieved a plateau for supine mini percutaneous nephrolithotomy stone free rates after the 45th case(6). In the present study, we achieved a satisfactory success rate after 20 f-URS cases. We believe that obtaining access to the stone is a more complicated process in percutaneous nephrolitotomy than gaining access to the kidney with flexible ureterorenoscope, which makes to LC of f-URS shorter. Longer operation time is associated with anaesthetic complications, increased cost, morbidity, and even mor- tality. When beginning to perform a new surgical tech- nique, unfamiliarity with surgical instruments, possible incompatibilities between the surgical team, and inabil- ity to make some decisions subcortically could make the operation time longer. Tanrıverdi and colleagues found 144 minutes of mean operation time after the first 15 PNL cases, and their operation time decreased to 90 minutes between the 45th and 60th cases(12). Moreover, Sahan et al. faced significant decreases in supine mini PNL operation time from the 1st -15th patients to the 46th to 60th patients; however, the authors did not ob- serve any reduction in operation time after 60 cases(6). We achieved significant reductions in preparation time and f-URS operation time after 30 cases. Fluoroscopically-guided diagnostic and therapeutic processes began to be performed more commonly all over the world in recent decades. The harmful impact of fluoroscopy on cancer development, eyes, and skin is well-known(13). Many studies which analyzed fluor- oscopy-assisted surgeries in urology ignored this situ- ation. Tanrıverdi et al. stated that fluoroscopy time de- creased from 17.5 minutes in the first 15 cases, to 8.9 minutes by the 60th case(9). Also, Sahan et al. found as- sociations between increased experience in supine mini PNL and reduction in fluoroscopy time(6). In the present study, we significantly reduced fluoroscopy time from the first 20 cases to 40th – 60th cases, and fluoroscopy time reached a plateau after the 60th case. The present study, the first prospective research to eval- uate LC in f-URS, has some limitations. The low num- ber of patients could be accepted as a limitation. Also, our study focused on one-month outcomes after f-URS, and the impact of LC on long-term outcomes of f-URS is lacking, which may be the subject of another study. Additionally, we did not analyse the effect of LC on cost-effectiveness of f-URS, which may be clarified in further studies. Lastly, the impact of LC on patient qual- ity of life was not evaluated in this prospective study. CONCLUSIONS The present study is the first to determine the learning curve of f-URS, and we found that the success of f-URS reached satisfactory levels after 20th cases. In addition, 40 cases may be enough for surgical proficiency regard- ing decreases in preparation time, operation time, and fluoroscopy time. Robotic & Laparoscopic Urology 429 Group 1 (n=20) Group 2 (n=20) Group 3 (n=20) Group 4 (n=20) P value F Preparation time (min)* 18.6 ± 4.8a 17.2 ± 4.7a 15.0 ± 4.9b 12.4 ± 2.2b 0.001 20.4 Operation Time (min)* 44.1 ± 5.8a 39.7 ± 5.8a 33.0 ± 5.0b 30.0 ± 4.4b 0.001 29.4 Fluoroscopy time (sec)* 82.9 ± 15.0a 62.1 ± 16.5b 50.3 ± 14.4c 41.7 ± 16.4c 0.001 26.07 Hospitalization time (hour)* 23.9 ± 7.1 24.7 ± 7.1 22.3 ± 7.9 23.3 ± 8.0 0.581 0.36 Stone free rate 13 (65%)a 17 (85%)b 17 (85%)b 18 (90%)b 0.037 Complications 3 (15%) 1 (5%) 1 (5%) 1 (5%) 0.712 Minor (Clavien-Dindo grade 1-2) 2 (10%) 1 (5%) 1 (5%) 1 (5%) Major (Clavien-Dindo grade 3-5) 1 (5%) 0 (0%) 0 (0%) *mean ± standard deviation Lower-case letters are used to define the group that makes the difference. The same letters (such as a-a) define that there is no difference, different letters (such as a-b) define that there is a difference. Table 3. 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Endourology and Stones diseases 271 Learning Curve of Flexible Ureterorenoscopy-Kezer et al. Endourology and Stones diseases 10