Reproducibility of rectal tumor volume delineation using diffusion-weighted MRI: Agreement on volumes between observers

To retrospectively evaluate the inter-observer agreement between a radiologist and a radiation oncologist and volume differences, in T2 and diffusion-weighted (DWI) MRI of gross tumor volume (GTV) delineation, in rectal cancer patients. Two observers, a radiologist and a radiation oncologist, delineated GTVs of 50 patients on T2-weighted MRI (T2GTV) and echo planar DWI (DWIGTV). Observers agreement was assessed using DICE index, Bland-Altman analysis and intra-class correlation coefficient (ICC). Student's t-test was used for GTV comparison. Median T2GTV and DWIGTV were 17.09±14.12 cm3 (1.92–62.03) and 12.79±12.31 cm3 (1.23–62.25) for radiologist, and 16.82±13.66 cm3 (1.78–65.9) and 13.72±12.77 cm3 (1.29–69.75) for radiation oncologist. T2GTV were significantly larger compared to DWIGTV (P