56 Chapter 4 Methods and materials Patient selection This study was performed as a side project of an ongoing IRB-approved retrospective multicenter imaging study focused on MRI for risk and response assessment in rectal cancer. Due to the retrospective nature of the study, informed consent was waived. As part of this multicenter project the primary staging MRIs including radiological staging reports, treatment specifics (type of surgery and type of neoadjuvant treatment, if any), and clinical outcome data of 1426 patients with biopsy-proven rectal adenocarcinoma were previously collected, originating from 10 Dutch medical centers (1 university hospital, 8 large teaching hospitals and 1 comprehensive cancer center). As part of this previous study project, the MRI examinations of a subset of the collected study patients were re-evaluated by a single dedicated MRI expert (DMJL with >10 years of experience in reading rectal MRI) from the principal investigating (PI) center according to the staging template published in the most recent ESGAR consensus guidelines on rectal MRI from 2018 (14). The reader was blinded for the original staging reports and any other clinical information regarding treatment or treatment outcome. For the current study we collected from this dataset all patients originating from the eight teaching hospitals in the cohort who fulfilled the following inclusion criteria: (a) availability of the original primary staging report, (b) availability of a second re-evaluation report by the MRI expert from the PI center. As the aim of this study was to evaluate staging trends and effects in a general hospital setting, only patient cases from the eight general teaching hospitals were included and cases from the academic and comprehensive cancer center (both expert referral centers for rectal cancer) were excluded. Classification of type and completeness of reporting A second independent observer other than the MR expert who performed the imaging re-evaluations (NB) reviewed the original radiological staging reports and classified the type of reporting as “free-text”, “semi-structured” or “template”. Reports were categorized as free-text when including only prose descriptions without any specific subheadings (apart from “findings” and/or “conclusion”) or standardized reporting items. Reports were classified as semi-structured when the report was organized using subheadings, including for example “tumor” (or “tumor stage”) and “nodes” (or “nodal stage”). Reports were classified as template reports if the report included an itemized list of reporting items, e.g., morphology, location, T-stage, N-stage, MRF, sphincter involvement, EMVI, etc. In addition, completeness of reporting was documented for each staging report by assessing for each item listed in the ESGAR structured report template whether it was explicitly reported, not explicitly reported but otherwise derivable from the report, or not reported at all.
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