“Micro Hand S” surgical robot vs laparoscopic gastrectomy for gastric cancer: comparison of short-term outcomes Running head: "Micro Hand S" robot vs laparoscopic gastrectomy

Background Expensive cost of surgery has limited the use of surgical robot in China. The emergence of “Micro Hand S” surgical robot provides more choices for surgical treatment. Our study was to evaluate the safety and feasibility of “Micro Hand S” surgical robotic gastrectomy for gastric cancer. Methods Perioperative data of 75 patients who underwent “Micro Hand S” surgical robotic gastrectomy (RG) or laparoscopic gastrectomy (LG) at the Department of General Surgery, Third Xiangya Hospital, Central South University from June 2017 to January 2019 were collected to compare the short-term outcomes between the two groups. Results No statistically significant difference was found in baseline characteristics between the two groups (P > 0.05). RG group had longer operation time (P < 0.01). The harvested lymph nodes were comparable between the two groups (P = 0.084). There were five positive margins in the LG group, and the R0 resection rate was comparable between the two groups (P = 0.247). 16 complications occurred in the RG group according to the Clavien-Dindo classification system, 6 in grade I, and 10 in grade II. 68 complications happened in the LG group, 22 in grade I, 44 in grade II, 1 in grade IIIa and 1 in grade IVa. The comprehensive complications index (CCI) was similar between the two groups (P = 0.895). Intraoperative blood loss, surgical resection, reconstruction of the digestive tract intraoperative blood transfusion, Chemoradiotherapy, pathological type, degree of differentiation, proximal resection margin, time of first flatus, time of liquid diet, time of abdominal drainage tube extraction, and hospital stay for RG and LG were similar too (P > 0.05). Conclusion “Micro Hand S” surgical robotic gastrectomy is safe and feasible.


Introduction
Gastric cancer, the fourth most common malignant tumor in the world, is also the second leading cause of death for all malignant tumors [1]. In China, gastric cancer ranks third in morbidity and mortality, causing a heavy disease burden [2]. Surgical operation is the main treatment for gastric cancer. Gastrectomy with lymph node dissection is the gold standard for the treatment of gastric cancer, and laparoscopic surgery has been the most commonly used surgical approach at present [3]. However, the laparoscopic approach has obvious limitations, such as two-dimensional vision, hand tremor amplification, limited range of motion, and uncomfortable posture [4]. Surgical robots-the inevitable outcome of the development of minimally invasive surgery-have some special advantages that laparoscopes do not have, including 3-dimensional amplificated vision, tremor filtering, motion scaling, and comfortable posture [5]. Since Hashizume et al [6] first reported the da Vinci gastrectomy in 2002, researches on robotic gastrectomy have increased [7][8][9]. In January 2019, the "Micro Hand S" surgical robot [10], independently developed in China for more possibilities of surgical treatment, successfully completed the phase I clinical trial. In this study, we compared the short-term outcomes between "Micro Hand S" surgical robotic gastrectomy (RG) and laparoscopic gastrectomy (LG) through retrospective analysis for evaluating the safety and feasibility of the robotic gastrectomy.

Patients
We retrospectively collected the perioperative data of 75 patients who underwent RG or LG at the Department of General Surgery, Third Xiangya Hospital, Central South University from June 2017 to January 2019. There were 15 cases in the RG group and 60 cases in the LG group.
Inclusion criteria were as follows: (1) complete perioperative data could be obtained; and (2) biopsy confirmation of gastric cancer. Exclusion criteria were as follows: (1) metastasis or complicated with other tumors; (2) gastric stump carcinoma or benign tumor; (3) leiomyoma or stromal tumor; (4) serious cardiopulmonary dysfunction or liver and kidney dysfunction; and (5) palliative operation. Preoperative examinations including blood and urine (routine examination), stool (routine examination), liver and kidney function, and blood coagulation function, along with electrocardiograms, investigation of tumor markers, ultrasound, computed tomography (CT) scans, and biopsy were performed to confirm the diagnosis. Patients were well informed of the surgical procedure and risks, complications, alternative treatments, and voluntarily signed informed consent. After the operation, patients were treated with gastrointestinal protective agents, antibiotics treatment, fluid infusion, nutritional support, maintenance of electrolyte balance, and other symptomatic treatments. Chemoradiotherapy was performed in line with Japanese gastric cancer treatment guidelines [11]. Our study was approved by the Institutional Review Board of the Third Xiangya Hospital and registered at ClinicalTrials.gov (NCT02752698).

Surgical procedure
In addition to trocar location and surgical instruments used, there was no significant difference between the RG and LG procedures for gastric cancer. Patients were first placed in the supine position; this was followed by routine disinfection and sterile drapes whisked onto the patients The clinical and pathological TNM stage referred to 8th edition of the AJCC TNM Staging System for Gastric Cancer [12]. CCI, a newly developed measurement method for complications, was calculated through http://cci.assessurgery.com online tools [13]. It integrates all recorded complications based on the Clavien-Dindo Complications Classification System [14] into a formula that is weighted by severity, ranging from 0 (no complications) to 100 (death). Comprehensive statistics of complications from mild to severe and quantification of results enable CCI to intuitively reflect the severity of postoperative complications.

Statistical Analysis
IBM SPSS Statistics version 20.0 was used for statistical analysis. Continuous variables were expressed as mean ± standard deviation (SD), and an independent sample t-test or Wilcoxon rank sum test were used. Categorical variables were compared through the Pearson χ 2 test or the Fisher's exact test. The Wilcoxon rank sum test was used for ordinal categorical variable.
All statistical analyses were two-sided, and P values less than 0.05 were considered statistically significant.

Baseline characteristics of patients
Baseline characteristics of patients are shown in Table 1. The mean age of patients in the RG group was 61.7±7.4 years and that in the LG group was 57.0 ± 12.3 years (P = 0.174). There were no significant differences in BMI, gender, ASA grade, tumor diameter, tumor location, clinical TNM stage or pathological TNM stage between the two groups (P > 0.05).

Surgical factors and pathological parameters
Surgical factors and pathological parameters are presented in Table 2. All operations were successfully completed, and no conversion or complications occurred during the operation.
Postoperative pathological results showed that the pathological type of all gastric cancers was adenocarcinoma. The operative time was longer in the RG group than in the LG group (365.6 ± 48.7 min vs. 298.6 ± 70.9 min, P < 0.01). There was no significant difference in intraoperative blood loss, gastric resection, reconstruction, intraoperative blood transfusion or Chemoradiotherapy between the two groups (P > 0.05). The histological type, Lauren's classification and proximal resection margin were not significantly different across the RG and LG groups. All tumor margins were negative, except in five specimens from the LG group.
The R0 resection rates were similar between the two groups (P = 0.238). And the harvested lymph nodes were also comparable between the RG group and the LG group

Postoperative outcomes and complications
Postoperative outcomes and complications are shown in Table 3 and Table 4, respectively.
There was no significant difference between the two groups in time The CCI was comparable between the two groups (13.5 ± 12.3 vs. 13.7 ± 14.6, P=0.895). All patients were discharged smoothly. One patient of LG group died within 90 days after surgery due to poor physical condition and no further operation occurred.

Discussion
Surgical robots with several advantages, such as three-dimensional imaging, high flexibility of instruments, hand tremor filtering, and humanized operating platform, are designed to overcome the limitations of laparoscopy. The research of surgical robots has gradually become a hot issues. New robotics technologies are emerging [15], such as the Invendoscopy E200 system, Flex® robot system, Senhance, Auris robotic endoscope system, and "Micro Hand S" surgical robot [10,16]. The results of this study showed no statistically significant difference was observed in baseline characteristics between RG and LG groups, so clinical outcomes of these two groups could be compared. The surgical results showed that RG group had a longer operation time than LG group. It was because the operative time was increased due to inexperience and equipment installation. As technology advances and experience increases, we think the surgical time can be reduced [17]. The number of harvested lymph nodes in RG group was comparable with that in LG group (P = 0.084), which may be related to the small sample size. There was no significant difference in CCI between the two groups (P = 0.895). Although there was no significant difference in the R0 resection rate between the two groups (P = 0.238), it was clear that five patients in the LG group had residual margin cancer, and no residual cancer occurred in the RG group. Three-dimensional field magnification and motion scaling of robotic surgery may be helpful in the precise removal of a mass. Perhaps a statistical difference can be found when a larger sample size was provided. Of course, there are some limitations in our study. First, this study was retrospective and may be affected by selection bias. Second, the sample size was small witch could reduce the accuracy of surgical results. Third, the follow-up period was too short, and long-term follow-up and survival analysis is needed for the malignant tumor. Our medical center will be responsible for a multi-center, randomized, controlled clinical trial of "Micro Hand S" surgical robot , and the results will be reported later.

Conclusion
Ultimately, "Micro Hand S" surgical robotic gastrectomy is safe and feasible. And there will be one more choice of surgical procedure for patients in the future. We will continue evaluate the prognosis and quality of life of patients.

Author Contributions
Shaihong Zhu, Guohui Wang, Bo Yi, Zheng Li, Yong Liu and Yuanbing Yao contributed to the conception/design of the work. Yuanbing Yao and Yong Liu contributed to the acquisition of data. Yuanbing Yao and Yong Liu contributed to the analysis/interpretation of data. Yuanbing Yao drafted the manuscript. Shaihong Zhu, Guohui Wang, Bo Yi and Zheng Li revised the manuscript. All authors have approved the final version submitted and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.