PROFICIENCY-GAIN CURVE AND COSTS ANALYSIS IN ROBOTIC RECTAL RESECTION WITH TME FOR CANCER: A COMPARISON BETWEEN DA VINCI SI AND XI SURGICAL SYSTEMS

Background Several studies about surgical benefits and differences between da Vinci Si and Xi surgical systems are reported in literature. However, there are no studies analyzing the influence of proficiency-gain curve on costs. The aim of this study is to compare the effects of learning curve on surgical outcomes and costs in robot assisted colorectal surgery for rectal cancer. Methods From April 2010 to April 2017, 90 robotic rectal resections were performed at our Institute with the da Vinci Si (Si-RobTME), or with the da Vinci Xi (Xi-RobTME), since January 2016. Based on CUSUM analysis 80 cases were selected and divided in two comparable groups of 40 consecutive Si-RobTME and Xi-RobTME respectively. The costs of the two procedures were analyzed according to the robotic proficiency-gain curve. Results The CUSUM proficiency-gain curves of the two groups were identical, and were divided into two phases: Si1 and Xi1 (cases 1–19) and Si2 and Xi2 (cases 20–40). No differences in the preoperative data, surgical procedure and pathological data were documented. A hybrid laparoscopic/robotic approach was used in 17 cases (42,5%) in the Si-RobTME group while all the procedures of the Xi-RobTME group were completed with a full robotic approach (p <0.001). Overall median operative time (OT) was significantly lower in Xi-RobTME than in Si-RobTME (275 vs 312.5 min, p = 0.021). The OT resulted significantly lower in late phases, Si2 and Xi2, according with robotic learning curve progression (p<0.001), and in phase Xi2 than in phase Si2 (265 vs 290 min, p=0.052) with a reduction of personnel costs (1151.6 vs 1260.2, p=0.052). Statistically significant reduction in overall variable costs (OVC) and consumable costs (CC) were found comparing early and late robotic phases (p < 0.001). Xi2 phase costs resulted lower than Si2 phase costs (OVC: 7983 vs 10231.9, p=0.009, CC: 3464.4 vs 3869.7, p