Comparison of Robotic Rectal Resection for Cancer Between the da Vinci Si and Xi: A Cusum and Costs Analysis

Aim: No studies have analyzed the possible difference of learning curve and costs between da Vinci Si and the new da Vinci Xi. The aim of this study is to compare surgical parameters and costs of robotic surgery in rectal cancer with the use of these two different da Vinci surgical systems. Methods: From April 2010 to April 2017, 90 robotic rectal resections were performed at our Institution with the da Vinci Si (Si-RobTME), until December 2015, or with the da Vinci Xi (Xi-RobTME), since January 2016. Based on CUSUM analysis, two comparable groups of 40 consecutive Si-RobTME and 40 consecutive Xi-RobTME were identified. Data of the prospectively collected database were retrospectively compared. Costs of the two procedures were analyzed according to the robotic learning curve. Results: The CUSUM learning curves of the two groups identified two similar phases in both groups: Si1 and Xi1: cases 1–19; 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, in contrast to no cases in the Xi-RobTME group (p<0.001). A statistically significant reduction in OT by phase of robotic experience was detected (p <0.001), and resulted lower in the phase Xi2 than 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 reductions in overall variable costs (OVC) and consumable costs (CC) were found between robotic phases (p < 0.001), and resulted lower in the Xi2 phase respect than Si2 phase (OVC: 7983 vs 10231.9, p=0.009, CC: 3464.4 vs 3869.7, p<0.001). Conclusion: The similar learning curve for both groups were likely due to a ‘proficiency-gain effect’ related mainly to the use of a new robotic technology and not to the surgical operation itself. We reported a significant optimization of costs with the surgeon’s experience and the new technology. This result is mainly due to the shorter OT and a reduction of personnel and consumable costs because of the higher percentage of a full robotic approach performed with the da Vinci Xi.