Comparative evaluation of CT and CT/MR DWI images for GTV delineation in precision radiotherapy for esophageal squamous cell carcinoma

Objective: To evaluate the difference between CT and CT/MR DWI images for gross tumor volume (GTV) delineation in precision radiotherapy for esophageal squamous cell carcinoma. Methods: 20 patients with pathologically confirmed as esophageal squamous cell carcinoma were selected for target delineation. The GTV based on CT and CT/MR DWI images of the patients were delineated by six radiation oncologists. The mean, standard deviation, coefficient of variation (CV = standard deviation/mean) of GTV volume, the ratio of minimum value and maximum value (ratio = maximum value/minimum value) of the GTV volume were calculated. And the CV and ratio of the GTV by the two methods were compared. Results: The biggest difference of GTV volume on CT and on CT/MR DWI images was 55.71 and 13.89 cm³ (F = 12.80, P < 0.05). The CV on CT and CT/MR DWI images were 0.30 ± 0.08, 0.11 ± 0.04 (Z = -3.92, P < 0.05), and the ratio of GTV volume were 2.38 ± 0.62, 1.34 ± 0.13, respectively (Z = -3.92, P < 0.05). Conclusions: CT/MR DWI images could display GTV more directly, which may help to increase consistency of GTV for esophageal squamous cell carcinoma delineation among different radiation oncologists. (authors)