This thesis covers the development of a theoretical model of macroscopic vascularized tumor growth, the analysis of morphological characteristics, blood flow and tissue oxygenation in dependence on the vascular network in which the tumor grows, as well as an analysis of potential barriers to drug delivery caused by the transport characteristics of tumor blood vessel networks and tissue. An extended model is developed, incorporating processes of angiogenesis, vaso-dilation, vessel regression and collapse, for tumors embedded in artificial arterio-venous networks. It is predicted that substances dissolved in blood are rapidly conducted in maximal concentrations through most parts of the tumor network. Simulations of interstitial fluid flow and spatio-temporally variable drug concentrations showed that the local tumor vascular density predominantly determines the dose delivered and that non-diffusive substances may not reach all areas of tumors due to the heterogeneity of interstitial fluid flow. Moreover a new computational model to determine coupled intravascular and tissue oxygen concentrations was conceived which is applied to simulated tumor blood vessel networks guided by optical mammography data. Random differences of initial vessel layouts can accordingly explain the blood oxygen saturation fluctuations observed in tumors of a cohort of patients, to some degree. However other factors such as vessel compression need to be taken into account.
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