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Page 8 of 14 Abe et al. Mini-invasive Surg 2023;7:28 https://dx.doi.org/10.20517/2574-1225.2023.15

Figure 3. The CUSUM plot of console time. A plateau was reached after the 29th case, followed by a further decrease after 43 cases.
Therefore, we defined the period up to the 28th case as phase I, the period from the 29th-42nd cases as phase II, and the period after
the 43rd case as phase III.

two groups during the entire study period. In the introductory phase (phase I), there were no cases
requiring salvage surgery after CRT. Patients who had lower or abdominal esophageal cancer tended to be
more common in the RAMIE group. There were more cT3 cases in phase II than the other phases. There
were more cases of middle and lower thoracic esophagus in phase I compared to the other phases,
indicating that more typical cases tended to be selected in the introductory phases.

Surgical outcomes
Table 2 shows the surgical outcomes. The median thoracic procedure time was 232 min for MIE and 239
min for RAMIE, with no difference between the two groups. The R0 resection rate was 92% for MIE and
90% for RAMIE, with no significant difference between the groups.

Postoperative mortality, morbidity, and short-term outcomes
Table 3 shows the postoperative short-term outcomes. There were no postoperative in-hospital mortalities
in the MIE or RAMIE groups. The 90-day mortality rates for MIE and RAMIE were 1.4% and 0,
respectively. All patients were discharged to home. The RLN palsy rate was 25% in the MIE group compared
to 18% in the RAMIE group. Although the incidence of RLN palsy was slightly higher in the RAMIE group
(29%) in the introductory phase (phase I) compared to the MIE group, the incidence was lower in the
RAMIE group (12.5%) in phases II and III, at which time RAMIE became more standardized. The incidence
of postoperative pneumonia was 20% in the MIE group and 18% in the RAMIE group, with no difference
between the groups. The incidence of anastomotic leakage was 8% in the MIE group and 1% in the RAMIE
group (P = 0.029). No difference was detected between MIE and RAMIE in surgical technique in the gastric
tube reconstruction, and we believe that the MIE group incidentally had more anastomotic leakage cases.
The incidence of chylothorax was 32% higher in phase I compared to MIE (P = 0.01), which decreased to
16% in phase II/III (P = 0.618).

The median postoperative hospital stay was 18 days in the MIE group compared to 15 days in the RAMIE
group (P < 0.001). Notably, the median postoperative hospital stay was significantly reduced to 14.5 days in
the RAMIE during phases II and III. We believe that the difference between the groups may be influenced