Effect of contrast enhancement in delineating GTV and constructing IGTV of thoracic oesophageal cancer based on 4D-CT scans

Objective: To investigate the effect of contrast enhancement on delineating the gross tumour volumes (GTVs) of different respiratory phases and constructing the corresponding internal GTVs (IGTVs) of primary thoracic oesophageal cancer based on four-dimensional computed tomography (4D-CT) scans.

Methods: Forty-five patients with upper (14 cases), middle (16 cases), or lower (15 cases) thoracic oesophageal cancer sequentially underwent conventional plain and contrast-enhanced 4D-CT scans during free breathing. First, the GTVs were delineated on plain 4D-CT, and the corresponding IGTVs were constructed by a physician. Then the GTVs were delineated on contrast-enhanced 4D-CT images, and the corresponding IGTVs were constructed by the same physician using the same standards.

Results: The coefficient of variation for the target volume delineated on contrast-enhanced 4D-CT images was constantly smaller than that for plain 4D-CT images. The length of the GTVs along the z axis, as well as the volumes of the GTVs that were delineated and the IGTVs that were constructed, did not change between contrast-enhanced and plain 4D-CT images in patients with upper or lower thoracic oesophageal cancer (P>0.05), but showed significant differences in patients with middle thoracic oesophageal cancer (P<0.05).

Conclusions: Contrast-enhanced 4D-CT scans can reduce the error of target volume delineation and be used to construct a more accurate internal target volume in patients with middle thoracic oesophageal cancer, however, whether GTV delineation or IGTV construction for patients with upper or lower thoracic oesophageal cancer, no significant benefit was found from contrast-enhanced 4D-CT scan.