Caren van Roekel

10 Chapter 1 tolerable dose on the parenchyma and the minimum tumor-absorbed dose required for response). This is of vital importance to obtain the best possible response for each patient while maintaining safety. The first aspect of 166 Ho- radioembolization that can be used to develop a tailored treatment approach that was investigated in this thesis was the quality of life after radioembolization (Chapter 3). Quality of life is especially important in patients of advanced age, with a shortened life expectancy. Therefore, the impact of treatment strategies on quality of life should be known before making a treatment decision. The second aspect comprised of the logistics of radioembolization: should the preparatory angiography and the treatment procedure be performed on a single day, which could be beneficial for patients with highly progressive disease, or is it better to separate the preparatory angiography from the treatment procedure (Chapter 4)? Also, the outcome after radioembolization was assessed. If the type of progression is known, which can be either based on growth of existing intra- or extrahepatic lesions, or on new intra- or extrahepatic lesions, this could possibly be linked to prognostic characteristics and be used for patient selection (Chapter 5). A key assumption for treatment planning is the existence of a dose-response relationship. This was investigated first in a mixed-tumor type cohort (Chapter 6) and secondly in colorectal cancer patients only (Chapter 7). In this last group, the dose-toxicity relationship was also investigated. The results of these studies, specifically the obtained dose thresholds, will be used for future patients. Finally, the impact of catheter-related techniques on treatment outcomes were assessed. First, the efficacy of coil-embolization to obtain intrahepatic redistribution was analyzed (Chapter 8). Secondly, the impact of an anti-reflux catheter on treatment outcomes was assessed in a prospective trial (Chapter 9). The hypothesis of the use of an anti-reflux catheter was that this may lead to a higher tumor- to non-tumor activity concentration ratio: (partial) obstruction of the vascular lumen induces a decreased downstream pressure, possibly leading to a better tumor targeting (9-14).