Caren van Roekel

213 The efficacy of coil-embolization in radioembolization (QuiremSpheres ® , Quirem Medical B.V.). Patients were included if they had undergone embolization of at least one tumor-feeding arterial branch. Patients were excluded when post-treatment imaging was not available. Both angiography images and cone-beam CT images, acquired during the work-up procedure of the included patients, were reviewed to identify the coil- embolized artery and the liver volume that was vascularized by it (i.e. dependent liver volume). Baseline characteristics were obtained, including type of primary tumor, gender, age, injection sites, and interval between coil-embolization and radioembolization. Our institute’s medical ethics committee waived the need for informed consent for this retrospective study. Qualitative analysis Distribution was analyzed qualitatively by visual assessment performed by two nuclear medicine physicians with >5 years of experience with radioembolization. Data on gender, age, embolized artery, dependent embolized segment, intended target volume, and relevant information regarding patients’ medical history (e.g. history of hepatic surgery, radio frequency ablation) was provided. Relevant digital subtraction angiography images and cone-beam CT images were also available. All other data was blinded. The redistribution was visually rated in a nominal scale: 1) no redistribution, 2) dubious redistribution, and 3) successful redistribution. Rating was performed independently, and any disagreement was resolved by consensus. Quantitative analysis The distribution of microspheres was also analyzed quantitatively by measuring the average activity concentration in the dependent segments (i.e. segments that rely on a coil-embolized artery for blood supply), using post-treatment imaging. These activity concentrations were compared to the activity concentrations measured in non-dependent segments (i.e. all liver segments that did not rely on the coil-embolized artery). The activity concentration in dependent tumors was also compared to the activity concentration in non- dependent tumors. 8