Table 1.

Variable category definition and variable sets

Variable categories	Features
1. Non-imaging	Age, sex, time between CRT and surgery, tumor morphology (polyp, semicircular, or circular) and tumor height (distal-mid versus proximal-rectosigmoid)
2a. Basic imaging staging (original reports)	cT-stage (cT12, cT3, cT4), cN-stage (cN0, cN1, cN2), involvement of the mesorectal fascia (MRF-, MRF+)
2b. Basic imaging staging (expert re-evaluation)	cT-stage (cT12, cT3, cT4), cN-stage (cN0, cN1, cN2), involvement of the mesorectal fascia (MRF-, MRF+)
3. Advanced imaging staging (expert re-evaluation)	All variables included in 2b (basic imaging staging—expert re-evaluation) + cT-substage (cT12, cT3abcd, cT4ab), extramural invasion depth, EMVI, tumor length
4. Quantitative imaging (derived from T2W-MRI and ADC)	Tumor volume*, mean, median, minimum, maximum, variance, mean absolute deviation, range, robust mean absolute deviation, root mean squared, 10th percentile, 90th percentile, energy, entropy, interquartile range, kurtosis, skewness, total energy, uniformity
Variable sets
1. Non-imaging only 2. Non-imaging + basic imaging staging (original reports) 3. Non-imaging + basic imaging staging (expert re-evaluation) 4. Non-imaging + advanced imaging staging (expert re-evaluation) 5. Non-imaging + quantitative imaging 6. Non-imaging + basic imaging staging (original reports) + quantitative imaging 7. Non-imaging + basic imaging staging (expert re-evaluation) + quantitative imaging 8. Non-imaging + advanced imaging staging (expert re-evaluation) + quantitative imaging

* Tumor volume was derived directly from the whole-tumor segmentations