A comparison of contrast-to-noise ratio of liver tumors between dynamic contrast-enhanced (DCE) CT and respiration-tracked 4D-CT for radiotherapy targeting

Objectives We compare the contrast-to-noise ratio (CNR) of tumours on 4D-CT and DCE-CT and explore how DCE-CT can be used to enhance tumour delineation for radiotherapy targeting. Methods A total of 18 intrahepatic lesions from 15 patients were included in this study. 8 patients with primary hepatocellular carcinoma, and 7 metastatic patients with a total of 10 tumours, underwent DCE-CT and respiration tracked 4D-CT. Both 4D-CT and DCE-CT were acquired at 120 kVp, but with 600 and 1920 mAs, respectively. CNRs were calculated for each lesion for each image set and compared using paired t-test. Results DCE-CT image sets had CNRs which were higher than those of 4D-CT image sets. The improvement in CNR was significant for lesions that were metastatic rather than primary, for lesions that were smaller than the mean size (5.7 cm), and for lesions which had undergone prior treatment rather than those which had not. Conclusions Target volume delineation in liver radiotherapy is challenging due to the inherent low tumour CNR. DCE-CT significantly improves CNR in liver metastases compared to 4D-CT, the current standard for radiation treatment planning. Considerations for DCE-CT include patients with metastatic lesions, additional iodinated contrast and CT dose. Advances in Knowledge DCE-CT combined with 4D-CT can offer advantages in delineating small, previously-treated metastatic tumours for radiotherapy.