# Robotic evolution from Si to Xi in rectal cancer assessing operative performance and oncological outcomes

## TL;DR

This study compares two robotic surgical systems for rectal cancer and finds that the newer Xi system offers better surgical efficiency without compromising cancer outcomes.

## Contribution

The study provides a direct comparison of perioperative and oncologic outcomes between two robotic platforms (Si and Xi) in rectal cancer surgery.

## Key findings

- The Xi system showed shorter operation, console, and docking times compared to the Si system.
- The Xi system resulted in less blood loss and shorter hospital stays without affecting oncologic outcomes.
- In low rectal cancers, the Xi system had a higher sphincter preservation rate.

## Abstract

To compare perioperative and oncologic outcomes between robotic surgical platforms (Si vs. Xi) in rectal carcinoma.

A retrospective cohort study of 86 robotic rectal cancer resections (Si: n = 31; Xi: n = 55) were analyzed at Tianjin Medical University Cancer Hospital between November 2019 and June 2024.

Among 86 patients with comparable baseline clinicopathological variables (all p > 0.05), the Xi system showed superior perioperative efficiency: shorter operation (226.7 vs. 282.1 min, p = 0.010), console (p = 0.016) and docking times (p = 0.013), less blood loss (83.8 vs. 155.8 mL, p = 0.005), and a shorter postoperative stay (7.8 vs. 9.7 days, p = 0.016). On multivariable analyses, Xi remained independently associated with a shorter operative time (p = 0.002), reduced blood loss (p = 0.027), and decreased length of stay (p = 0.038). Complication rates, lymph node yield, and short-term oncologic quality indicators (distal resection margin [DRM], circumferential resection margin [CRM], mesorectal integrity) were comparable between two systems (all p > 0.05). In low rectal cancers (≤ 5 cm from the anal verge) with balanced baselines, Xi achieved a higher sphincter preservation rate (90.5% vs. 55.6%, p = 0.049). Survival trends numerically favored Xi (3-year DFS 79.8% vs. 73.0%; OS 92.0% vs. 83.0%), but differences were not significant (DFS: p = 0.54; OS: p = 0.26). On Cox regression, TNM stage independently predicted both DFS (p = 0.041) and OS (p = 0.029). However, the robotic platform (Xi vs. Si) showed no survival advantage (DFS: HR = 1.33, 95% CI 0.53–3.37, p = 0.548; OS: HR = 1.43, 95% CI 0.76–2.67, p = 0.267).

Compared with Si, the Xi platform confers measurable perioperative advantages—shorter operative time, less blood loss, and reduced hospitalization—without compromising short-term oncologic quality or survival. In low rectal tumors, Xi may facilitate sphincter preservation under comparable baselines. Long-term outcomes appear driven primarily by disease stage rather than platform generation.