Optimization of a protocol for contrast-enhanced four-dimensional computed tomography imaging of thoracic tumors using minimal contrast agent

PURPOSE: The accuracy of target delineation for node-positive thoracic tumors is dependent on both four-dimensional computed tomography (4D-CT) and contrast-enhanced three-dimensional (3D)-CT images; these scans enable the motion visualization of tumors and delineate the nodal areas. Combining the two techniques would be more effective; however, currently, there is no standard protocol for the contrast media injection parameters for contrast-enhanced 4D-CT (CE-4D-CT) scans because of its long scan durations and complexity. Thus, we aimed to perform quantitative and qualitative assessments of the image quality of single contrast-enhanced 4D-CT scans to simplify this process and improve the accuracy of target delineation in order to replace the standard clinical modality involved in administering radiotherapy for thoracic tumors. METHODS: Ninety consecutive patients with thoracic tumors were randomly and parallelly assigned to one of nine subgroups subjected to CE-4D-CT scans with the administration of contrast agent volume equal to the patient’s weight but different flow rate and scan delay time (protocol A1: flow rate of 2.0 ml/s, delay time of 15 s; A2: 2.0 ml/s, 20 s; A3: 2.0 ml/s, 25 s; B1: 2.5 ml/s, 15 s; B2: 2.5 ml/s, 20 s; B3: 2.5 ml/s, 25 s; C1: 3.0 ml/s, 15 s; C2: 3.0 ml/s, 20 s; C3: 3.0 ml/s, 25 s). The Hounsfield unit (HU) values of the thoracic aorta, pulmonary artery stem, pulmonary veins, carotid artery, and jugular vein were acquired for each protocol. Both quantitative and qualitative image analysis and delineation acceptability were assessed. RESULTS: The results revealed significant differences among the nine protocols. Enhancement of the vascular structures in mediastinal and perihilar regions was more effective with protocol A1 or A2; however, when interested in the region of superior mediastinum and supraclavicular fossa, protocol C2 or C3 is recommended. CONCLUSION: Qualitatively acceptable enhancement on contrast-enhanced 4D-CT images of thoracic tumors can be obtained by varying the flow rate and delay time when minimal contrast agent is used.