Caren van Roekel

139 Mode of progression after radioembolization in colorectal cancer patients situ, time since diagnosis of metastases, WHO performance status, KRAS wild type versus KRAS mutation, pre-treatment CEA level, primary tumor location (categorized as left sided (splenic flexure to rectum) or right sided (proximal to the splenic flexure)) and tumor load (percentage liver involvement, categorized as <25%, 25-50%, >50%) (21, 25, 27-33). Radioembolization The prescribed activity for the patients that were treated with glass 90 Y-microspheres was calculated according to the Medical Internal Radiation Dose (MIRD) method, with a desired absorbed dose of 80-120 Gy, according to the instructions for use (34-36). Visual and quantitative assessment of 99m Tc- MAA distribution is weighted in this decision, also considering whole liver treatment in one session or sequentially. For the patients that were treated with resin 90 Y-microspheres, the body surface area (BSA) method was used. The injected activity for 166 Ho-microspheres was calculated based on the MIRD method with an aimed whole-liver absorbed dose of 60 Gy (37). Response assessments Two blinded readers independently performed measurements for tumor diameter on abdominal contrast-enhanced CT or MRI at baseline and three- months follow-up, using the same modality at both time points, according to RECIST version 1.1 (17). In case no consensus was reached, a third reader gave the final call. Finally, inter-observer variability between the two raters was assessed. Response at three months was dichotomized as disease control (i.e. complete or partial response (CR or PR) and stable disease (SD)) or progressive disease (PD). For a more detailed assessment of mode of progressive disease a further subdivision was made in four categories: growth of intrahepatic metastases, growth of extrahepatic metastases, new intrahepatic metastases, and new extrahepatic metastases. All extrahepatic metastases were taken into account, regardless of their size. Statistical analyses Standard descriptive statistics were used to display patient demographics and summarize response measures. Cohen’s kappa was used to determine agreement. Chi-Square was used to test for differences in whole body response 5