A prospective randomized comparative trial of da Vinci SP versus da Vinci Xi in colon and rectosigmoid cancer surgery: a single-center, open-label study protocol

Abstract

Background

Colorectal cancer surgery increasingly emphasizes not only oncological outcomes but also postoperative recovery and patient-centered outcomes. Robotic-assisted surgery has gained widespread acceptance, and the da Vinci Single-Port (SP) system has emerged as a novel platform that may further reduce surgical invasiveness compared with the conventional multi-port da Vinci Xi system. However, current evidence comparing these platforms in colon cancer surgery remains limited to retrospective studies.

Methods

This study is a single-center, open-label, prospective randomized controlled trial designed to compare the da Vinci SP and Xi systems inpatients undergoing curative robot-assisted surgery for clinical stage 0–III colon or rectosigmoid adenocarcinoma. A total of 200 patients will be randomly assigned in a 1:1 ratio to the SP or Xi group. The primary endpoint is postoperative pain assessed using the Numerical Rating Scale on postoperative days 1 and 3. Secondary endpoints include operative variables, postoperative complications, inflammatory markers, pathological outcomes, and patient satisfaction.

Conclusions

This trial is expected to provide prospective evidence on the clinical value of the SP platform and to support evidence-based decision-making in robotic colon cancer surgery. The trial has been registered with the University Hospital Medical Information Network Clinical Trials Registry (UMIN-CTR: R000065814).

Trial Registration

UMIN-CTR R000065814 (2025/4/13) Saitama Medical University International Medical Center.

Introduction

Background (6a, 6b, 7)

Colorectal cancer (CRC) is increasing globally and is a leading cause of cancer-related mortality [1]. Treatment modalities for CRC have expanded in recent years to include surgery, chemotherapy, and radiation therapy [2, 3]. Furthermore, patient needs extend beyond cancer cure to include quality of life (QOL) considerations post-surgery [4].

In the field of CRC surgery, the adoption of robot-assisted surgery is rapidly advancing. Reports have demonstrated the utility of various robotic platforms, including da Vinci Xi [5, 6], Senhance Digital Laparoscopy [7], Hugo [8], and Hinotori [9]. For rectal cancer, robot-assisted surgery may contribute to better postoperative functional preservation compared with laparoscopic surgery, suggesting a growing demand for this approach [10].

Similarly, single-port laparoscopic surgery has been associated with higher patient satisfaction than conventional laparoscopic surgery [11]. Single-incision laparoscopic colectomy (SILC), which uses an umbilical incision, has been reported to have comparable short- and long-term outcomes to conventional laparoscopic surgery for CRC [12, 13]. However, the technical difficulty of SILC and the potential for instrument clashing have prevented it from becoming a standard procedure [14, 15].

Recently, the da Vinci SP platform was developed, and its utility has been reported in various surgical fields. The da Vinci SP platform allows for the operation of multi-jointed instruments through a single incision. Retrospective studies and propensity score matching analyses from South Korea comparing SP and Xi for both colon and rectal cancer suggest that SP may be associated with less pain and a shorter postoperative hospital stay, with no significant differences in postoperative complications or operative time, thus potentially maintaining safety [16, 17]. A 2025 review reported outcomes for 396 colorectal cases treated with SP, noting an incision length of 4 cm and a low rate of intraoperative complications [18].

Nevertheless, these reports are exclusively retrospective, and selection bias may exist due to factors such as surgeon preference or patient characteristics. Consequently, prospective randomized comparative trials are required to clarify the true superiority of SP and demonstrate its clinical utility. This study aims to compare the short-term outcomes of the SP and Xi platforms in colon cancer surgery using a randomized controlled trial (RCT) framework. The primary endpoint is postoperative pain, while secondary endpoints include safety, operative time, blood loss, oncological completeness, and patient satisfaction.

Methods and design

Trial design (8a, 8b, 9, 20, 22, 24)

This is a single-center, open-label, 1:1 randomized parallel-group comparative trial comparing the da Vinci SP system (SP Group) with the da Vinci Xi system (Xi Group) in robot-assisted surgery for colon and rectosigmoid cancer. This confirmatory trial is designed to examine whether SP can reduce postoperative pain without compromising perioperative safety and oncological radicality compared with the conventional multi-port robotic system Xi. The trial will be conducted at Saitama Medical University International Medical Center in Japan. This trial was registered with the UMIN Clinical Trials Registry (UMIN-CTR: R000065814 (2025/4/13)) prior to patient enrollment and has received approval from the institutional ethics committee. Written informed consent will be obtained from all eligible patients prior to enrollment.

Eligibility criteria (10)

Inclusion criteria

1. Patients with pathologically confirmed colon or rectosigmoid adenocarcinoma.

2. Patients with clinical stage 0–III colon or rectosigmoid cancer scheduled for curative resection with robot-assisted surgery.

3. Patients with primary tumor located in the cecum, ascending colon, sigmoid colon, or rectosigmoid junction.

4. Patients aged 18–80 years at the time of informed consent.

5. Patients with Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1.

6. Patients with no history of laparotomy (history of appendectomy only is acceptable).

7. Patients capable of understanding the study content and providing written informed consent independently.

Exclusion criteria

1. Patients with active synchronous malignancy requiring treatment.

2. Patients with a history of organ transplantation.

3. Patients who have received preoperative chemotherapy, radiotherapy, or immunotherapy for the target tumor, including patients with MSI-high tumors who have received short-course preoperative immunotherapy.

4. Patients with severe and uncontrolled comorbidities such as congestive heart failure, end-stage renal disease, liver cirrhosis, or poorly controlled diabetes.

5. Patients with active systemic or intra-abdominal infection.

6. Patients with severe psychiatric or neurological disorders that would interfere with study participation or protocol adherence.

7. Patients who are pregnant or breastfeeding.

8. Patients with a strong preference for either the SP or Xi procedure.

9. Patients deemed inappropriate for trial participation by the principal investigator for reasons other than those listed above.

Rectal cancers were excluded because preoperative treatment is frequently administered in these patients at our institution, which may affect postoperative pain and other perioperative outcomes. Tumors of the transverse colon and descending colon were also excluded because variations in the extent of lymph node dissection and surgical procedures according to tumor location could introduce heterogeneity and affect the study outcomes.

Interventions (11a)

All enrolled patients will undergo lymph node dissection and complete mesocolic excision in accordance with the Japanese colorectal cancer treatment guidelines [19].

SP group

Patients assigned to the SP group will undergo robot-assisted surgery using the da Vinci SP platform. The approach will be through a single umbilical incision. After completing lymph node dissection and bowel mobilization, the specimen will be extracted through the umbilical incision using a wound protector. For rectosigmoid lesions, a 12-mm port will be added in the right lower abdomen to use a stapler for bowel resection. For colonic cases, no additional ports will be placed. Reconstruction will be performed using functional end-to-end anastomosis (FEEA) for colonic cases and double stapling technique (DST) for sigmoid colon and rectosigmoid cases.

Xi group

Patients assigned to the Xi group will undergo multi-port robot-assisted surgery using the da Vinci Xi platform. Standard multi-port trocar placement will be used, adhering to guideline-specified lymph node dissection and mobilization ranges. The specimen will be extracted through an umbilical incision using a wound protector. Reconstruction will be performed using the same methods as in the SP group. In colonic cases, FEEA is performed extracorporeally in all patients and is standardized across both groups.

Surgeons

Surgeons will be board-certified by the Japan Society for Endoscopic Surgery and will have performed ≥ 40 da Vinci Xi cases. Surgical procedures and dissection ranges were standardized in a technical manual. To exclude initial learning curve cases for SP, surgeons will have performed ≥ 10 SP cases. In addition, surgeon identity and prior SP experience will be recorded, and exploratory analyses adjusted for surgeon-related factors will be performed to assess the potential impact of the learning curve.

Intervention modifications and discontinuation criteria (11b)

If serious complications occur during surgery, conversion to open surgery or laparoscopic surgery will be performed.

Perioperative care (11d)

Perioperative management will actively promote early mobilization starting from postoperative day 1 (POD 1). Oral intake will begin with water on POD 1, and soft or regular diet will be initiated on POD 2–3 if there are no complications. All patients will be managed under a standardized ERAS protocol. Postoperative pain management will include intravenous patient-controlled analgesia (PCA) with standardized settings across both groups, including the analgesic agent, dose, and lockout interval, as well as scheduled acetaminophen. Additional nonsteroidal anti-inflammatory drugs or opioids will be administered as needed. Total postoperative opioid consumption will be recorded.

Outcome measures (12)

Primary endpoint (16a)

The primary endpoint is postoperative pain intensity assessed using the maximum NRS values on POD1 and POD3. These are prespecified assessment time points for a single primary endpoint, and the primary analysis will treat them as repeated continuous measures. Pain assessment will be conducted by ward nurses blinded to the treatment allocation at predetermined times (every 8 h postoperatively), and NRS values will be recorded as continuous variables (Table 1).

Table 1.

Schedule of assessments and procedures

Secondary endpoints

• Operative time (skin incision to skin closure)

• Console time

• Blood loss

• Conversion rate to open surgery or laparoscopic surgery

• Intraoperative complications (requiring additional procedures)

• Postoperative complications within 30 days (Clavien–Dindo classification ≥ 3) [20].

• Postoperative length of hospital stay (from surgery date to discharge date)

• Inflammatory markers on postoperative day 1 and day 3 (CRP value, albumin)

• Pathological findings: TNM classification (UICC 9th edition), number of harvested lymph nodes, R0 resection rate

• Patient satisfaction at discharge and 3 months post-surgery, assessed using a brief questionnaire evaluating overall surgical experience and satisfaction with scar appearance (2-question, 5-point scale; Appendix 1)

• Extraction-site wound length

• Total postoperative opioid consumption

• Incisional hernia during longer-term follow-up

Sample size (14)

Previous retrospective studies and observational studies have suggested that SP may reduce postoperative pain compared with the multi-port Xi system; however, effect sizes vary, and high-quality randomized trial evidence is scarce. In this trial, assuming a medium effect size (Cohen’s d = 0.5) for the difference in maximum pain scores between SP and Xi on postoperative day 1 and day 3, with a two-sided significance level of α = 0.05 and statistical power (1-β) = 0.80, the required sample size to detect this difference is 64 cases per group.

The medium effect size of 0.5 was determined based on previous reports of pain differences of approximately 0.5–2 scores on postoperative day 1, assuming a standard deviation of 2 for the NRS. Assuming a standard deviation of 2 points in NRS, a Cohen’s d of 0.5 corresponds to an absolute between-group difference of approximately 1 point. We considered this magnitude to be clinically meaningful in the context of postoperative pain after minimally invasive colorectal surgery.

To enhance the robustness and reliability of the study results, the target enrollment will be increased to 100 patients per group (total n = 200). This expanded sample size is expected to improve statistical power and reduce the risk of type II error, thereby increasing the likelihood of detecting clinically meaningful differences between the SP and Xi groups.

Randomization and allocation (16a, 16b)

Patients who meet the eligibility criteria and provide written consent will be randomly assigned to the SP or Xi group in a 1:1 ratio. Randomization will be based on a computer-generated allocation sequence using variable block sizes. The allocation will be performed by the Data Manager.

The following factors will be used for stratification:

1. Tumor site (colon (cecum/ascending colon) vs. Sigmoid colon/Rectosigmoid junction)

2. Clinical stage (stage 0–II vs. stage III)

The allocation result will be notified to the surgical team before the operation. Complete blinding of the surgeon and patient is impossible due to the nature of the intervention. However, efforts will be made to blind outcome evaluators and statistical analysts to the allocation group (pain assessment will be conducted by ward nurses blinded to the treatment allocation, and analysis will be performed using an anonymized dataset) (Fig. 1).

Fig. 1.

Flow diagram

Statistical analysis (20a, 20b, 20c, 21b)

Analysis will primarily follow the Intention-to-Treat (ITT) principle, including all randomized patients according to their assigned group. For the primary analysis, the maximum NRS scores on POD1 and POD3 will be analyzed as repeated continuous measures using a mixed-effects model including treatment group, time point, and group-by-time interaction. No additional imputation will be performed for missing data. Continuous variables such as operative time, blood loss, postoperative length of hospital stay, and CRP values will be reported as medians with interquartile ranges and compared using Student’s t-test or the Mann–Whitney U test. Categorical variables such as the conversion rate to open surgery, postoperative complication rate, and R0 resection rate will be presented as frequencies and percentages and compared using the χ² test or Fisher’s exact test. The analysis of secondary endpoints is exploratory, and no adjustment for multiplicity will be performed. A two-sided p-value < 0.05 will be defined as statistically significant. Statistical analysis will be performed using JMP Pro 19 (SAS Institute Inc., Cary, NC, USA).

Coordinating center (5d)

The coordinating center for this study will be established at Saitama Medical University International Medical Center. The coordinating team will consist of the principal investigator, a data manager, a monitoring manager, and a statistician. The principal investigator will provide overall leadership and ensure strict adherence to the protocol. The project manager will be responsible for the day-to-day operation of the trial, communication with participating institutions, and management of the research schedule. The data manager will oversee data collection and entry, ensuring data quality and completeness.

Data management (19)

An enrollment form must be completed for each registered case and submitted to the Center for Clinical Research Promotion. Registration data will be stored for five years. The anonymized dataset and analysis code for this trial will be made available upon reasonable request following publication of the results.

Confidentiality (27)

Since this is an in-house clinical study conducted solely by our institution, with all data analysis also performed internally, no personal information of research subjects (such as names, IDs, or dates of birth) will be disclosed externally during the study. Adequate consideration will be given to protecting the privacy of research subjects upon publication.

Trial status (15)

This study is currently ongoing. Patient enrollment has commenced, and as of March 20, 2026, six patients have been enrolled. No interim analysis has been conducted, and the study remains in the protocol phase.

Safety monitoring (21a, 22)

Serious adverse events will be reported to the hospital director within 24 h in accordance with internal regulations and promptly submitted to the Institutional Review Board (IRB). Monitoring and voluntary audits will be conducted by the Clinical Research Center. Given the short-term endpoint and the use of approved devices, an independent Data Safety Monitoring Board (DSMB) will not be established. However, temporary suspension or termination of the trial will be considered if the rate of Clavien–Dindo Grade III or higher complications in the SP group is clearly higher than in the Xi group and the in-house safety review committee deems continued trial unsuitable.

Dissemination (31a, 31b, 31c)

This study adheres to the Declaration of Helsinki and the “Ethical Guidelines for Medical Research Involving Human Subjects.” Written consent will be obtained from all participants. Results will be published in academic conferences and peer-reviewed journals. Anonymized data will be shared upon request after publication, according to policy.

Discussion

Recent retrospective studies and propensity score matching analyses focusing on the colon and rectum have compared the short-term outcomes of SP and Xi. These studies suggest not only the equivalence of safety and oncological completeness (R0 rate, number of retrieved lymph nodes) but also a potential for shorter incision length and reduced postoperative pain in the SP group. However, these studies are predominantly single-center, small-cohort observational studies, which may not adequately control for confounding factors related to procedure selection or surgeon experience. Therefore, validation through a prospective randomized trial is necessary to assess the clinical utility of the SP system.

This trial employs a superiority design to test whether SP can significantly reduce postoperative pain compared with Xi. The sample size calculation, based on assuming a medium effect size (Cohen’s d = 0.5), supports a target enrollment of 100 patients per group, for a total of 200 patients. This ensures sufficient statistical power to detect a clinically meaningful difference in pain.

A key strength of this trial is the multifaceted evaluation of outcomes, which includes not only pain scores but also operative time; blood loss; complications (Clavien–Dindo classification); conversion rate; inflammatory markers (CRP, albumin); length of stay; pathological indicators (lymph node count, margin, R0 status); and patient satisfaction at discharge and 3 months post-surgery. While SP is expected to improve pain and cosmesis by reducing the incision size and port count, the introduction of multi-jointed instruments and different visualization techniques may affect the surgeon’s workflow. One study reported that the SP system imposes more mental and physical stress on the surgeon during vessel management and a higher stress load on the scrub nurses compared with Xi, indicating a potential increase in burden for the medical staff [21]. Consequently, it is necessary to demonstrate that the reduction in patient invasiveness goes beyond the superficial benefit of a “smaller incision” by also analyzing short-term safety indicators and inflammatory markers. Some reports comparing single-port laparoscopic surgery with conventional Xi have suggested that Xi resulted in less pain, indicating that da Vinci surgery might inherently reduce stress on the abdominal wall [22].

Furthermore, the evaluation of patient-reported outcomes (PROs), specifically patient satisfaction, immediately after discharge and at 3 months is highly significant. In laparoscopic colectomy, patient satisfaction has been reported to be higher with single-port laparoscopic surgery compared with conventional laparoscopic surgery [11]. Since SP is a single-port approach through the umbilicus, resulting in a less visible scar, it may offer an advantage over Xi in terms of cosmesis.

A strong feature of this trial design is its single-center implementation, which minimizes variability in procedure selection and perioperative management. Both groups will undergo robot-assisted radical resection according to Japanese clinical guidelines, utilizing standardized clinical pathways to suppress variation in outcomes caused by non-surgical factors. The selection of surgeons is also restricted, ensuring a baseline level of robotic surgical skill before evaluating the impact of SP introduction.

Conversely, several limitations are anticipated. First, complete blinding of patients and surgeons is impossible due to the trial design, introducing potential performance/expectation bias in pain and satisfaction evaluations. However, the primary endpoint, NRS, is a widely used and relatively objective scale, and bias is minimized by pre-specifying the timing of assessments. Second, as SP is a relatively new platform, completely excluding the influence of the surgeon’s learning curve is difficult. This is mitigated by restricting participating surgeons to those with ≥ 10 SP cases, thereby avoiding the most extreme initial learning phase outcomes.

Furthermore, as a single-center study, there are inherent limitations to the generalizability of the results. The results represent outcomes from experienced surgeons at a high-volume center in Japan; therefore, direct adoption by smaller facilities or those in the early phase of robotic implementation should be approached cautiously. Nonetheless, clearly describing the surgical procedures and perioperative management allows other institutions to reference this protocol and verify reproducibility, which is a crucial role of this study.

In conclusion, this randomized controlled trial aims to build evidence for the da Vinci SP single-port robotic platform by prospectively comparing short-term outcomes, including postoperative pain, between SP and Xi.

Author contribution

YI and YH conceived the study and led the overall study design. TF and HS contributed to the methodology, including the randomization scheme and statistical analysis plan. YI, YH, and CH developed the clinical protocol and coordinated trial implementation. TF and YM were responsible for participant recruitment and perioperative data acquisition. AN, YN, SA, and HH will oversee data management and monitoring procedures. YI, YH, and TF drafted the manuscript. CH and YH critically revised the manuscript for important intellectual content. All authors read and approved the final manuscript.

Funding

Open Access funding provided by Saitama Medical University This study is supported by Institutional Research Funds and the Hidaka Project (Saitama Medical University International Medical Center).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval

Saitama Medical University International Medical Center (Approval ID: R000065814RCT). 2025/10/28

Competing interests

The authors declare no competing interests.