Diffusion weighted imaging for gross tumor volume delineation in primary radiochemotherapy and image guided adaptive brachytherapy for cervical cancer
Accurate gross tumor volume (GTV) delineation is critical for successful radiochemotherapy and image-guided adaptive brachytherapy (BT) in cervical cancer. This study investigated whether diffusion-weighted imaging (DWI) improves GTV delineation accuracy compared to T2-weighted (T2w) MRI alone, across different physician experience levels. Twenty-seven patients with locally advanced cervical carcinoma undergoing primary radiochemotherapy were analyzed. Six physicians (three experts, three residents) delineated GTVs at three time points: diagnosis (init), pre-brachytherapy (preBT), and pre-brachytherapy with applicator in situ (BT). Segmentations were performed using T2w images alone and T2w plus DWI (b=800smm DWI guidance significantly improved inter-observer agreement among experts at init (conformity index: 0.62→ 0.70, p<0.05) and BT (0.33→ 0.39, p<0.05) time points. For residents, DWI guidance enhanced agreement with expert consensus, particularly during BT, with significant improvements in Dice coefficient (median increase 9%, p<0.05) and reduced Hausdorff distance (median decrease 1.3 mm, p<0.05). Tumor volume correlation between preBT and BT time points improved with DWI guidance for both groups. Incorporating DWI into the segmentation workflow reduces inter-observer variability for both expert and resident radiation oncologists. DWI guidance particularly benefits less experienced physicians, enabling them to achieve contours closer to expert consensus standards through additional functional information.