Caren van Roekel

187 Dose-effect relationships of holmium-166 radioembolization in colorectal cancer In case of fused lesions at follow-up, a volume-weighted average of the absorbed dose of the different components at baseline was calculated. Also, a weighted average, correcting for tumor volume, was calculated to obtain the mean tumor-absorbed dose per patient. The parenchymal-absorbed dose was determined using the activity in the entire (dilated) liver contour, with the activity in the (dilated) tumor regions subtracted. Toxicity Evaluation The emergence of clinical toxicity between treatment and three months post- treatment was recorded, with exception of clinical adverse events during the first week after treatment, to allow for distinction between adverse events due to embolization and adverse events due to radiation. Laboratory toxicity between treatment and three months post-treatment was evaluated using the following parameters: albumin, alkaline phosphatase (AP), alanine aminotransferase (ALAT), aspartate aminotransferase (ASAT), bilirubin and gamma-glutamyltransferase (GGT). Common terminology criteria for adverse events (CTCAE) version 5.0 was used for grading (14). Since version 5.0 allows for higher values of laboratory parameters when these were already abnormal at baseline, relative change in laboratory values between baseline and three months follow-up was calculated as well. Furthermore, presence of ascites and encephalopathy (as part of radioembolization-induced liver disease (REILD)) was determined at three-months follow-up. Efficacy Evaluation Metabolic response to treatment was evaluated on 18 FDG PET/CT at three- month follow-up. Tumors were automatically defined based on standardized uptake value (SUV) and lesion total lesion glycolysis (TLG) was obtained. To avoid misidentification, baseline and follow-up images were evaluated in parallel. Metabolic response of hepatic lesions was defined based on the change in TLG between baseline and follow-up, according to the PERCIST criteria (15). Hepatic tumor response was also assessed according to the Response evaluation criteria in solid tumours (RECIST) version 1.1 (16). 7