Can C-Arm Cone-Beam CT Detect a Micro-Embolic Effect After TheraSphere Radioembolization of Neuroendocrine and Carcinoid Liver Metastasis?

Rational and Objective: Radioembolization with yttrium-90 microspheres is a therapy that is used for hepatic tumors. 20-30 mu m microspheres loaded with Y90 are supposedly occluding tumor vessels at the capillary level. Then, these spheres deliver high-dose radiation to the tumor. However, this theoretical embolic effect has never been appreciated in imaging. Dual-Phase cone-beam computed tomography (DPCBCT) is a multi-phasic intra-procedural scan that uses only one contrast media injection to visualize early (feeding vessel) and delayed (capillary level) tumor enhancement. The purpose of this study was to determine whether there is a microembolic effect induced by TheraSpheres (R) (MDS Nordion, Ottawa, Ontario, Canada) at the capillary level by using DPCBCT imaging. Materials and Methods: 14 patients with 72 carcinoid or neuroendocrine tumors were treated with radioembolization, and all underwent DPCBCT (Allura Xper, Philips Healthcare) imaging before and immediately after radioembolization with TheraSpheres (R). Tumor enhancement was measured in each phase by drawing a region of interest within the tumors. Results: 72 tumors were evaluated: average tumor density in the early arterial phase was 241 and 230 Hounsfield units (HU) (p < 0.001) before and after radioembolization, respectively; the average density in the delayed arterial phase was 226 and 161 HU (p < 0.001) before and after radioembolization, respectively. Average difference in tumor attenuation before and after radioembolization in early arterial and delayed phase was 11 HU and 64 HU (p < 0.001), respectively. Conclusion: The significant decrease in tumor enhancement in the DPCBCT delayed phase after TheraSpheres (R) injection indicates that there is an appreciable microembolic effect at the tumor capillary bed level.