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

Abstract 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 (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. Results 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  Conclusion DWI resulted in smaller volumes delineation compared to T2-weighted MRI. Substantial and almost perfect agreements were reported for DWIGTV and T2GTV between radiologist and radiation oncologist. Due to the fact that DWI could be considered a simple technique for volume delineation for radiation oncologist, DWI could be used to improve quality in radiation planning for an accurate boost volume delineation when a dose escalation is investigated.