Comparative analysis of marginal profit between da Vinci SP and multi-port systems in colorectal cancer surgery: a single-center descriptive cost-accounting study.

Introduction
The global burden of colorectal cancer continues to rise, and minimally invasive approaches have become central to contemporary surgical management. In Japan, robotic surgery for colorectal cancer was covered by the national insurance system in 2018, which accelerated its clinical adoption. Among available robotic platforms, the da Vinci Xi system has become widely used in colorectal surgery. However, the economic sustainability of robotic surgery remains a major concern in hospital management.
Most previous economic evaluations in colorectal surgery have focused on comparisons between robotic multi-port surgery and conventional laparoscopy, often emphasizing total cost, acquisition cost, or hospital-level financial impact [1, 2]. More recently, the da Vinci single-port (SP) system has emerged as a reduced-port robotic alternative. Although the SP system has attracted growing clinical interest, its economic implications remain insufficiently characterized, particularly within the Japanese reimbursement environment.
Importantly, fixed costs such as capital investment, depreciation, lease arrangements, and accounting treatment vary substantially across institutions. As a result, direct comparisons based on total institutional cost may be difficult to generalize. From an operational perspective, an alternative approach is to focus on case-level procedural cost efficiency using standardized running costs incurred during routine clinical care. In this context, marginal profit, defined as reimbursement revenue minus institutionally standardized running costs, may provide a practical indicator for evaluating day-to-day procedural performance [3].
In our clinical practice, we observed that the SP platform may be associated with lower dependence on certain high-cost robotic consumables in selected colorectal procedures. This observation led us to hypothesize that structural constraints of the SP system may be associated with a more cost-conscious workflow. The present study was therefore undertaken to descriptively compare the marginal profit rates of conventional laparoscopy, da Vinci multi-port, and da Vinci SP in colorectal cancer surgery using institutionally standardized cost-accounting data from a single high-volume center.

Materials and methods

Study design and setting
This was a single-center retrospective descriptive cost-accounting study conducted at Saitama Medical University International Medical Center. We evaluated the standardized running cost structure and marginal profit of colorectal resections performed using three minimally invasive platforms: conventional laparoscopy (Lap), da Vinci multi-port (MP), and da Vinci single-port (SP). The study period extended from October 2024 to December 2025. Because platform selection in routine practice was influenced by clinical and logistical considerations, the present analysis was not intended to establish causal economic superiority, but rather to describe an observed institutional pattern in procedural cost efficiency.

Data sources and case identification
Surgical case data, including procedure labels and operative timestamps, were obtained from the institutional operating room registry. These records were linked to Japanese fee-for-service claims data and patient-level material utilization data using surgery date and patient identification number. The available dataset included case-level administrative and accounting variables, but did not contain case-level itemized consumable usage data.

Eligibility criteria
We included patients with resectable primary colorectal cancer who underwent minimally invasive surgery during the study period. The patient selection process is detailed in Fig. 1 of the 607 colorectal resections initially assessed during the study period, 13 Senhance cases and 19 open cases were excluded, leaving 575 cases for the final marginal profit analysis. Cases were also excluded if any of the following applied: (1) the procedure name in the surgical log could not be mapped to the corresponding accounting category; (2) linkage between the electronic medical record dataset and the integrated accounting file was inconsistent; (3) the total billed amount related to surgery was zero; (4) the billed amount for the surgical technique itself was zero; (5) multiple operations for the same patient on the same day could not be reliably allocated to an individual procedure, except when only one procedure corresponded to a surgical technique claim; or (6) the procedure was performed outside the standard operating rooms.

Standardized costing framework
All cost and revenue calculations followed the institution’s standardized accounting definition (version 2022.2.1). We employed a Time-Driven Activity-Based Costing (TDABC) approach to allocate variable costs precisely (Fig. 2). The daytime effective working window was defined as 8:30 to 17:30 (540 min), and overtime-related labor costs were adjusted using a multiplier of 1.25.

Institutionally standardized running costs
For the purpose of this study, institutionally standardized running costs were defined as the sum of case-level costs and time-based allocable operating costs associated with each procedure. These included the following components:reimbursable materials, derived from patient-specific material use data and calculated including 10% tax;

consumable materials, including procedure-level consumables and anesthesia- and transfusion-related consumables;

disposable attire items, counted per scrubbed staff member at ¥100/person;

indirect operating room cost allocation, calculated as ¥120/min multiplied by room time;

repair and maintenance allocation, calculated as ¥14/min multiplied by operative time;

personnel costs, including surgeon and anesthesiologist labor at ¥131/min and nursing labor at ¥48/min, calculated according to operative or room time; and

intraoperative drug cost, estimated as 85% of drug-related revenue. These components were selected to reflect practical procedure-level operating costs under our institution’s internal cost-accounting framework. Fixed costs, including capital investment, lease cost, and depreciation, were not included.

Revenue calculation
Surgical revenue was calculated from Japanese claims data by summing fee schedule points for the surgical procedure and related add-on fees. Under the Japanese statutory health insurance system, one reimbursement point is uniformly equivalent to 10 Japanese Yen (JPY). In accordance with our institutional accounting rule, anesthesia revenue was excluded from the revenue calculation.

Outcome measure
The primary outcome was marginal profit rate (MPR), defined as:where total cost refers to the institutionally standardized running costs described above. In this study, the MPR was used as an index of procedural cost efficiency under real-world operating conditions, excluding capital depreciation and other fixed institutional costs.

Statistical analysis
Because the aim of this study was descriptive rather than confirmatory, no formal hypothesis testing was performed. Results are presented as group-level averages and proportions. To improve descriptive transparency regarding variability and overlap between groups, 95% confidence intervals (CIs) were calculated for mean marginal profit rates. Accordingly, comparisons among platforms should still be interpreted as descriptive patterns within a single institutional cost-accounting framework rather than inferential evidence of causal superiority.
In an additional descriptive subgroup analysis, cases originally grouped as multi-port robotic surgery were further separated into da Vinci Xi and da Vinci 5. This supplementary analysis was performed to explore potential heterogeneity within the original multi-port cohort and was interpreted descriptively.

Ethical approval
This study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Review Board of Saitama Medical University International Medical Center (Approval No. 2022–035). The requirement for informed consent was waived because of the retrospective design and the use of anonymized data.

Results

Overall comparison of marginal profit rates
After exclusions, a total of 575 patients were included in the final analysis (Fig. 1). We compared average marginal profit rates across minimally invasive surgical platforms during the study period (Fig. 2). In general, the laparoscopic group showed the highest marginal profit rates in both colectomy and rectal procedures. Among robotic platforms, the da Vinci SP group showed numerically higher marginal profit rates than the da Vinci MP group across all evaluated categories.

Colectomy for malignancy
For colectomy performed for malignant disease (n = 316), the Lap group (n = 91) showed the highest marginal profit rate at 53.2%. Among robotic approaches, the da Vinci SP group (n = 91) demonstrated a higher marginal profit rate than the da Vinci MP group (n = 134), with values of 32.7% and 26.1%, respectively (Table 1 and Fig. 3).

Rectal resection by sub-procedure
To further examine platform-related differences in pelvic surgery, rectal resections (total n = 259) were categorized into anterior resection (AR; 75,460 points), abdominoperineal resection (APR; 83,930 points), low anterior resection (LAR; 83,930 points), and resection with transanal anastomosis (e.g., ISR; 100,470 points).
Across all categories, the laparoscopic group showed the highest mean marginal profit rates. Among robotic platforms, the da Vinci SP group consistently showed numerically higher mean marginal profit rates than the pooled MP group in each included rectal sub-procedure (Table 2 and Fig. 4): anterior resection, 43.0% vs 37.7%; abdominoperineal resection, 35.1% vs 33.7%; low anterior resection, 43.8% vs 41.7%; and transanal anastomosis, 47.9% vs 44.5%.
Although the same directional pattern was observed across all rectal sub-procedures, several subgroups were small, particularly the laparoscopic and SP cohorts in APR, LAR, and transanal procedures. These findings should therefore be interpreted with caution.

Additional descriptive analysis separating da Vinci Xi and da Vinci 5
In a supplementary platform-specific analysis, the final analytic cohort consisted of 118 laparoscopic cases, 131 da Vinci SP cases, 258 da Vinci Xi cases, and 68 da Vinci 5 cases. The descriptive results are summarized in Supplementary Table 1.
For colectomy, the mean marginal profit rates were 53.3% (95% CI, 52.4–54.3) for laparoscopy, 33.4% (95% CI, 32.1–34.7) for da Vinci SP, 28.1% (95% CI, 27.2–29.0) for da Vinci Xi, and 19.1% (95% CI, 16.3–21.9) for da Vinci 5.
For rectal resection, the corresponding values were 61.5% (95% CI, 59.7–63.2), 43.3% (95% CI, 41.2–45.4), 40.8% (95% CI, 39.8–41.7), and 35.6% (95% CI, 33.0–38.3), respectively.
These additional findings suggest that the previously observed difference between the SP group and the pooled multi-port cohort was not uniform across multi-port generations and should be interpreted in light of institutional adoption timing and workflow context.

Summary of observed pattern
Overall, within the present institutional cost-accounting framework and excluding depreciation, the da Vinci SP platform showed numerically higher marginal profit rates than the MP platform in both colectomy and the included rectal resection categories. In the combined rectal resection cohort, the overall MPR was 43.5% for the SP group (n = 38) compared to 39.6% for the MP group (n = 190). However, because this was a descriptive analysis without adjustment for case mix or formal statistical testing, these findings should be viewed as an observed operational pattern rather than definitive comparative proof.

Discussion
In this single-center descriptive cost-accounting study, we evaluated the marginal profit rates of three minimally invasive platforms used in lower gastrointestinal surgery using institutionally standardized running costs while excluding fixed costs such as depreciation. The principal finding was that, within this framework, the da Vinci SP platform showed numerically higher marginal profit rates than the da Vinci MP platform across the evaluated colorectal procedures [4].
This finding is noteworthy because the SP system is often presumed to be economically disadvantageous owing to dedicated platform-specific devices and a potentially high acquisition burden [5, 6]. However, many prior reports have focused on total cost, capital burden, or hospital-wide financial impact rather than on procedural cost efficiency during routine daily practice. By contrast, our analysis was designed to isolate an operational dimension of economic performance: the proportion of reimbursement revenue retained after subtraction of institutionally standardized running costs directly associated with each case.
From a hospital management perspective, this distinction is important. In environments where capital investment and depreciation are strongly influenced by local timing of purchase, contract arrangements, accounting treatment, and case volume, total-cost comparison may not adequately reflect the real-world efficiency of individual procedures. A marginal profit approach may therefore offer a pragmatic supplementary framework for examining day-to-day procedural performance [3].
The most important contribution of the present study is not to establish the economic superiority of a specific robotic platform, but rather to highlight the possibility that platform-related workflow behavior and resource utilization patterns may influence procedural profitability under real-world operating conditions.
The additional separation of the multi-port cohort suggested heterogeneity between da Vinci Xi and da Vinci 5 in this early institutional experience (Supplementary Table 1). In particular, the da Vinci 5 subgroup showed lower marginal profit rates than the Xi subgroup. This observation should be interpreted cautiously, because it may reflect temporal adoption effects, learning-curve effects, changes in device utilization, or other workflow-related factors rather than intrinsic platform disadvantage.
One possible interpretation is that platform-related workflow behavior and resource utilization patterns may have influenced procedural profitability. However, because itemized device-level consumable data were not available in the present dataset, this interpretation remains speculative. Although the concept of a more constrained or cost-conscious workflow remains clinically plausible, it could not be directly tested in the present study.
In our current practice, SP procedures are also subject to platform-specific device constraints. Unlike da Vinci Xi and da Vinci 5, dedicated robotic staplers and vessel sealing devices are not currently available for SP in the same manner. As a result, when stapling or vessel sealing was required during SP procedures, laparoscopic devices were used as needed. This difference in device availability may have influenced workflow and consumable utilization, but the present dataset did not allow direct quantitative assessment of that effect.
Another notable finding was that procedures involving transanal anastomosis showed relatively favorable marginal profit rates across platforms (Lap 64.1%, SP 47.9%). These procedures may intuitively be expected to incur greater cost because they often involve two-team coordination. In our setting, however, several factors may help explain the observed pattern. First, the Japanese reimbursement system provides relatively favorable reimbursement for such procedures (100,470 points) compared to standard anterior or low anterior resections (75,460 and 83,930 points, respectively), expanding the revenue denominator. Second, simultaneous abdominal and transanal dissection may shorten overall workflow in selected cases, limiting time-driven indirect costs (Table 2 and Fig. 4). Third, the transanal component is typically performed using conventional lower-cost instruments rather than additional robotic consumables. These interpretations remain exploratory and should be tested in future workflow-based analyses.
From this perspective, the SP platform may have practical financial relevance not because it is inherently inexpensive, but because under selected real-world conditions it may be associated with a workflow that limits reliance on premium robotic consumables. This distinction may be of particular interest to hospitals seeking to optimize robotic surgery within existing reimbursement constraints.

Limitations
This study has several limitations. First, it was a retrospective single-center analysis, and the findings may reflect institution-specific practice patterns, surgeon preferences, case allocation, and accounting rules. Second, no adjustment was performed for patient background, disease complexity, tumor location, operative difficulty, surgeon preference, or temporal factors related to platform adoption. Third, several subgroup analyses involved small numbers, particularly in some rectal sub-procedure categories. Fourth, the dataset used in this study did not include case-level itemized consumable variables such as stapler cartridge counts, robotic stapler use, robotic energy device use, or assistant-port instrument substitution. Therefore, the proposed workflow-related explanation could not be directly tested and should be regarded as speculative. In our current practice, dedicated robotic staplers and vessel sealing devices are not available for SP in the same manner as for da Vinci Xi and da Vinci 5, and laparoscopic devices were used as needed during SP procedures. This may have influenced workflow and consumable utilization, but the present dataset did not allow quantitative assessment of that effect. Fifth, additional separation of the original multi-port cohort into da Vinci Xi and da Vinci 5 suggested heterogeneity within the multi-port group; however, because da Vinci 5 was introduced later in the study period, this subgroup remains susceptible to temporal bias and learning-curve effects. Finally, this study deliberately excluded capital investment, lease-related cost, depreciation, and other fixed institutional expenses; therefore, the findings do not directly address platform acquisition decisions or full hospital-level return on investment.

Future directions
Future studies should include multicenter validation, case-mix adjustment, and device-level cost analysis. In particular, it will be important to determine whether the observed patterns persist after adjustment for procedure type, tumor location, surgeon experience, and specific consumable usage. Such analyses would help clarify whether the present findings reflect workflow effects, case selection, resource utilization patterns, or a combination of these factors.

Conclusion
In this single-center descriptive cost-accounting study of colorectal cancer surgery using institutionally standardized running costs excluding depreciation, the da Vinci SP platform showed numerically higher marginal profit rates than the pooled multi-port cohort. Additional separation of the multi-port group suggested heterogeneity between da Vinci Xi and da Vinci 5 in this early institutional experience. These findings do not establish the economic superiority of any specific platform, but rather suggest that workflow behavior and resource utilization patterns may influence procedural profitability under real-world conditions. Further studies incorporating case-mix adjustment and device-level consumable analysis are warranted.

Supplementary Information
Below is the link to the electronic supplementary material.