Study Design
A retrospective review of a prospectively maintained rectal cancer databases in a public quaternary centre (Peter MacCallum Cancer Centre, Melbourne, Australia) was carried out. Consecutive patients undergoing minimally invasive (laparoscopic and robotic) proctectomy between January 2017 and June 2020 were included. Patients who had resections due to lesions higher than 15 cm from the anal verge excluded. Demographic characteristics, baseline clinical, tumour and operative variables, perioperative, histopathological outcomes and costs were compared between the laparoscopic and robotic groups. Subsequently, univariate, and multivariate analyses utilising demographic, baseline clinical and surgical variables were performed to identify the drivers of costs during the inpatient episode and examine the impact of the surgical approach on the overall costs.
Definitions and Clinical Outcomes
All cancer cases were discussed in a multidisciplinary team meeting. The surgical approach was decided on a case-by-case basis with input from a multidisciplinary team discussion and the robotic platform availability.
The clinical and histopathological staging was recorded according to the TNM classification (AJCC 8th Edition for Cancer Staging)[21]. The pre-treatment imaging assessment and re-staging were based on results from a CT, PET-CT, and pelvic MRI. Tumour height was defined clinically, endoscopically or by the pre-treatment MRI, with the anal verge as the reference point.
Extended resections were defined as per the Beyond TME Collaborative in any procedure that requires an en-bloc removal of an adjacent pelvic organ due to invasion or circumferential margin threatening by the primary rectal tumour[22]. Pelvic sidewall dissections were indicated when there were suspicious lymph nodes in the common or external iliac territories, obturator fossa or internal iliac system based on size criteria in the MRI (short-axis equal or greater than 7mm in the pre-treatment MRI, and equal or greater than 5mm in the post-treatment MRI if long-course chemoradiation therapy was delivered).
Complications, readmissions, and mortality up to 90 days after surgery were considered and recorded. Complications were classified according to the Clavien-Dindo classification[23].
The histopathological evaluation considered an R0 resection as a resection margin of > 1 mm. R1 resection was the presence of microscopic residual disease 1 mm or less from the resection margin, whereas R2 resection was the presence of macroscopic residual disease.
Financial Outcomes
Individual patients’ costs were retrieved via the Business Intelligence and Analytics
Department of the hospital. These included real costs from the inpatient episode, thus no estimated values were used. All costs were recorded as Australian Dollars (A$) and were obtained from the databases in November 2021. Costs were classified in theatre, hospitalisation, and overall costs. Theatre costs included consumables, medications, nursing staff, theatre utilisation and recovery expenses. Hospitalisation costs included ICU and ward expenses, medical and nursing staff, allied health staff, medication, transfusions and laboratory and imaging testing costs. Overall costs were the combination of total theatre and hospitalisation costs.
Procedures
All patients had mechanical bowel preparation. General anaesthetic was given, and prophylactic antibiotics were administered at induction. An indwelling urinary catheter was inserted, and the patient was placed in the Lloyd-Davies position. All patients had sequential compression devices and low molecular weight heparin was given on induction, and throughout the hospital stay. The splenic flexure was mobilised in all restorative cases and selectively in non-restorative cases. For cancer patients, a high ligation of the inferior mesenteric vessels was performed. Laparoscopic TME was undertaken utilising a five-trocar technique. The dissection followed the TME plane which was continued down to the level of the pelvic floor and then, the rectal transection was carried out using laparoscopic linear staplers in restorative cases. All robotic TME cases were performed with the Da Vinci Xi Surgical System (Intuitive Surgical, Sunnyvale, CA, USA). Four robotic ports and an assistant port were used in all cases. Procedures were performed in a totally robotic fashion. After the pelvic dissection, rectal transection was carried out utilising robotic linear staplers if a restorative case was performed. When a taTME approach was added, the procedure was carried out as a synchronous two-team operation. The transabdominal component of taTME was either robotic or laparoscopic according to the surgeons’ preference and platform availability. Details of our setup and steps have been previously published by the authors[24]. Anastomoses in the taTME group were mostly performed utilising a single-stapled double-purse string technique as described in the literature[25].
Statistical Analysis
Continuous variables were described as mean and SD. Categorical variables were described as frequencies and percentages. Chi-square or Fisher’s exact tests were utilised to compare categorical variables. Students’ t-test was used to compare continuous variables. Given the skewed distributions of economic outcomes, a GLM with gamma distribution and log-link function was used to identify the drivers of overall costs in this study. Those variables with a P value < 0.1 in the simple linear regression analysis were considered significant and were entered into the GLM. Additionally, a GLM in a backwards fashion was conducted by manually removing variables starting from the one with the highest P-value until only keeping those significantly related to overall costs. All statistical analyses were performed using the IBM SPSS Statistics for Windows, Version 27.0 (Armonk, NY, IBM Corp).
Ethics
A local Institutional Review Board ethics approval was obtained (QA/80014/PMCC-2021-283105).