Comparison of the Gross Target Volumes Based on Diagnostic PET/CT for Primary Esophageal Cancer

Abstract

Background: Clinically, many esophageal cancer patients who planned for radiation therapy have already undergone diagnostic Positron-emission tomography/computed tomography (PET/CT) imaging, but it remains unclear whether these imaging results can be used to delineate the gross target volume (GTV) of the primary tumor for thoracic esophageal cancer (EC).

Methods: Seventy-two patients diagnosed with thoracic EC had undergone prior PET/CT for diagnosis and three-dimensional CT (3DCT) for simulation. The GTV_3D was contoured on the 3DCT image without referencing the PET/CT image. The GTV_PET-ref was contoured on the 3DCT image referencing the PET/CT image. The GTV_PET-reg was contoured on the deformed registration image derived from 3DCT and PET/CT. Differences in the position, volume, length, conformity index (CI), and degree of inclusion (DI) among the target volumes were determined.

Results: The centroid distance in the three directions between two different GTVs showed no significant difference (P > 0.05). No significant difference was found among the groups in the tumor volume (P > 0.05). The median DI values of the GTV_PET-reg and GTV_PET-ref in the GTV_3D were 0.82 and 0.86, respectively (P = 0.006). The median CI values of the GTV_3D in the GTV_PET-reg and GTV_PET-ref were 0.68 and 0.72, respectively (P = 0.006).

Conclusions: PET/CT can be used to optimize the definition of the target volume in EC. However, no significant difference was found between the GTVs delineated based on visual referencing or deformable registration whether using the volume or position. So, in the absence of planning PET-CT images, it is also feasible to delineate the GTV of primary thoracic EC with reference to the diagnostic PET-CT image.

Keywords: 18F-FDG PET/CT; deformable image registration; gross target volume; thoracic esophageal cancer; three-dimensional computed tomography.

Figure 1

(A, B) Representative images in transversal, sagittal, and coronal sections show an ideal match between the before images and after images using DIR. The gray images represent images before deformable registration, and the red images represent images after deformable registration.

Figure 2

Representative images contoured in the image sessions in the transversal (a1), sagittal (a2), and coronal sections (a3) show differences among the three target volume delineations. The yellow contour represents the GTV_3D, the red contour represents the GTV_PET-ref, and the green contour represents the GTV_PET-reg. GTV, gross target volume; GTV3D, GTV contoured based on 3DCT without referencing 18F-FDG PET/CT; GTVPET-ref, GTV contoured on 3DCT referencing 18F-FDG PET/CT; GTVPET-reg, GTV contoured on the deformed image derived from 3DCT and 18F-FDG PET/CT using MIM deformable registration software.