Heterogeneity of skewness in T2w-MR images of locally advanced rectal cancer relates with response to neoadjuvant chemoradiotherapy

Purpose or Learning Objective To investigate how the heterogeneity of skewness (HoS) in locally advanced rectal cancer (LARC) imaged with T2 weighted (T2w) MRI before neo-adjuvant chemoradiotherapy (nCRT) can allow predicting responder patients based on the Tumour Regression Grade (TRG). Methods or Background Forty patients with LARC diagnosis undergo 1.5T-MRI before nCRT. Regions of Interest (ROIs) are manually segmented in all slices of the tumour’s site on the oblique axial T2w sequences. Based on the TRG assigned at the histopathological inspection of the surgical resection samples, the dataset is split into 15 responders (Rs) and 25 non-responders (NRs), having TRG=[0,1] and TRG=[2,3], respectively. HoS in LARC is computed on T2w values stemming from the measures of local asymmetry of each voxel. One-tail Wilcoxon rank-sum test (p<0.05) is considered to assess R and NR separability. Median values and interquartile ranges (IQRs) are considered to evaluate how the pre-therapy heterogeneity varies between Rs and NRs. Results or Findings HoS of Rs patients has a lower variance (IQR=0.15) than HoS of NRs ones (IQR=0.46), although median HoS has an opposite behaviour, being higher in Rs groups (4.08) than in NRs one (3.68). This yields Rs and NRs groups to be clearly separated (p~10-5), with non-overlapping IQRs. Conclusion In pre-therapy LARC imaged with T2w MRI, the higher the HoS, the better the response to nCRT. In addition, while the Rs group shows a homogeneous behaviour, the group of NRs is spread over a wider heterogeneity range, probably due to a higher variability of tumour characteristics. Limitations This study includes a limited number of patients, but the clear separation between R and NR highlights the promising role of heterogeneity, to be confirmed increasing the number of patients considered.