Data collection and statistical analysis
Clinical, surgical, histopathological and follow-up data were collected
from medical records. Baseline characteristics were compared between the
different learning phases. The institutional review board approved this
study and waived individual consent requirements for the use of these
pseudonymised retrospective data. Participants were not involved in the
development of this analysis and no core outcome sets were used in this
study.
Primary outcome of interest was surgical proficiency when introducing a
novice, based on cervical recurrence rate. To evaluate surgical
proficiency (i.e. learning curve) in this new phase, a risk-adjusted
cumulative sum analysis (RA-CUSUM) was performed (see previous
publication for a detailed description of this
analysis8). The probability of recurrence for each
individual patient was modelled by a multivariate logistic regression
analysis. To prevent overfitting, we limited this model to three degrees
of freedom. As previously described, we used two RA-CUSUM functions: the
RA-CUSUM+ chart, designed to detect a doubling of the odds of
recurrence, and the RA-CUSUM- chart, designed to detect a
halving of the odds of recurrence. Details of these RA-CUSUM functions
are provided in the supplementary material (Appendix S1).
Secondary outcomes were disease-free survival (DFS), disease-specific
survival (DSS) and overall survival (OS) in this new phase compared to
the previous phases. Survival was defined as the time interval between
date of diagnosis or first visit and date of disease recurrence
diagnosis (DFS), diagnosed clinically, by imaging, or histopathological
biopsy, or death due to the sequelae of cervical cancer (DSS) or death
from any cause (OS). Survival curves were estimated using Kaplan-Meier
method and the newly added group (group 3) was compared with the
previous groups (group 1 and group 2) using log-rank test: group 1
versus group 3 and group 2 versus group 3.
In addition to the previous analysis, we also assessed differences in
operation time and short-term surgical complications between the three
learning phases. Operation time was defined as the time (in minutes)
between first incision and end of closure by the surgeon. If the
procedure was performed in two tempi the operation time of the uterine
procedure was included in the analysis. All intraoperative
complications, defined as complications diagnosed intraoperatively and
postoperative complications within 42 days were registered in adherence
to the Common Terminology Criteria for Adverse Events (CTCAE) version
5.0 (published November 27, 2017).27 In the current
analysis main focus was on severe surgical complications, i.e. grade 3
to 5 adverse events.
Continuous data were compared between the groups using one-way analysis
of variance (ANOVA) or its non-parametric counterpart, as appropriate.
In the event of significance, post-hoc tests were conducted to determine
differences between each pair of groups. Categorical data were reported
as proportions and compared between groups using chi-square test or
Fisher’s exact test, as appropriate. Statistical tests were two-sided
with significance set at p<0.05, with confidence intervals
(CI) at the 95% level.
Analyses were performed using the Statistical Package for the Social
Sciences version 27.0.0 (SPSS; International Business Machines, Armonk,
NY, USA) and Microsoft Excel 2016 (Microsoft, Redmond, WA, USA).
Results