Robotic-Assisted Compartmental Dissection for Retroperitoneal Sarcoma: A Feasibility Study on Cadavers with the Da Vinci Xi System

Technical Summary: Robotic-Assisted Compartmental Dissection for Retroperitoneal Sarcoma

Problem Statement
Retroperitoneal sarcomas (RPS) present significant surgical challenges due to their large size (median ~20 cm), heterogeneous histology, and proximity to major vascular and visceral structures. The current standard of care is radical open multivisceral resection to achieve oncologically adequate margins; however, this approach carries high morbidity and persistent local recurrence rates. While minimally invasive and robotic techniques have advanced in other oncologic fields, their application in RPS remains limited. Critics argue that the tumor size and the necessity for specimen extraction often contradict a minimally invasive approach. Furthermore, there is a lack of standardized protocols for robotic port placement, anatomical reach, and workflow for the complex, compartmental dissection required in RPS surgery.

Methodology
This study is a two-phase, preclinical cadaveric feasibility study (IDEAL-D Stage 0) conducted at the University Medical Center Hamburg-Eppendorf using the da Vinci Xi Surgical System. The research involved three human cadavers with intact abdominal anatomy and no prior malignancy.

• Phase 1 (Trocar Optimization): Two sarcoma surgeons iteratively tested four different trocar configurations on two cadavers (one fresh-frozen, one Fix for Life [F4L] immersion) to determine optimal port templates for right- and left-sided access. The evaluation focused on ergonomics, arm conflict, external collision, and qualitative reach toward anatomical targets.
• Phase 2 (Confirmatory Dissection): Using the selected port templates, the surgeons performed a complete six-stage compartmental resection on both the right and left sides of a third cadaver (F4L immersion, stored three months post-fixation). The protocols followed established open surgical concepts: Radaelli et al. for the right side and Baia et al. for the left side.
• Assessment Framework: The confirmatory dissection was evaluated using:
  1. A novel 5-point Likert scale for anatomical reach at 50 predefined landmarks (1 = no useful reach; 5 = full unrestricted reach).
  2. An adapted System Usability Scale (SUS).
  3. A structured safety surrogate log to monitor critical structures (aorta, vena cava, nerves, etc.).
  4. Comparative tissue handling ratings for the different cadaver preservation methods.

Key Contributions

• Standardized Port Templates: The study identified side-specific, reproducible port configurations:
  • Right-sided: A horizontal suprasymphysial linear arrangement (analogous to oncologic right hemicolectomy).
  • Left-sided: An oblique line from the xiphoid to the right lower quadrant.
• Workflow Validation: The authors successfully mapped the robotic approach to the full six-stage compartmental resection concept, demonstrating that the robotic platform can technically replicate the extensive dissection required for RPS, including multivisceral resection and preservation of critical structures like the femoral nerve and iliac vessels.
• Tissue Handling Insights: The study provided comparative data on cadaver preservation, identifying F4L-immersion cadavers stored for three months post-fixation as superior for tactile feedback and tissue pliability compared to fresh-frozen or immediately used F4L specimens.

Results

• Anatomical Reach: All predefined landmarks were reached bilaterally. The pooled median reach score was 5/5 (range 3–5). The only instances of reduced reach (score of 3) occurred during initial access/exploration and specific pelvic steps requiring redocking. The dominant limiting factors were arm conflict during pelvic transitions and reach limitations during medialization of the pancreas/spleen on the left.
• Inter-Rater Agreement: There was substantial agreement between the two surgeons (90% overall exact agreement; quadratic-weighted Cohen's κ = 0.64).
• System Usability: The adapted SUS score was 72.5/100, exceeding the average benchmark of 68. Surgeons rated 3D visualization and instrument articulation highly, particularly for dissection around the vena cava, renal hilum, and femoral nerve.
• Safety: No unintended major injuries to critical structures occurred. Minor grasper impressions were noted on the inferior vena cava and bowel, but no transections or perforations were observed.
• Feasibility: The six-stage protocols were completed bilaterally without abandonment due to exposure issues or technical limitations.

Significance and Claims
The authors position this study as a "proof of concept" rather than a justification for routine clinical adoption. The primary significance lies in demonstrating that a da Vinci Xi-assisted approach can technically reproduce the standardized, extensive compartmental resection required for RPS in a tumour-free model.

The paper explicitly states that these findings do not justify widespread in vivo application for all primary RPS cases, particularly given the challenges of bulky tumors, specimen extraction, and the lack of data on bleeding or long-term oncologic outcomes. Instead, the study provides a structured starting point for:

1. Developing standardized training modules and port templates for robotic RPS surgery.
2. Guiding cautious, stepwise, and data-driven evaluation in carefully selected patients (e.g., smaller tumors, recurrent cases, or specific histologic subtypes) at specialized centers.

The authors conclude that while robotic assistance may offer advantages in specific scenarios (such as preserving structures beneath a tumor or reducing incision size for extraction), the transition to clinical practice must remain conservative and grounded in the oncologic principles established for open surgery.