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

Purpose: 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.

Materials And Methods: Two observers, a radiologist and a radiation oncologist, delineated GTVs of 50 patients on T2-weighted MRI (T2) and echo planar DWI (DWI). Observers agreement was assessed using DICE index, Bland-Altman analysis and intra-class correlation coefficient (ICC).