1. A method for planning and guidance of tumor ablation therapy in a target organ based on a patient-specific model, comprising: generating a patient-specific anatomical model of the target organ and a circulatory system of the target organ from medical image data of a patient, wherein generating the patient-specific anatomical model of the target organ and the circulatory system of the target organ comprises generating a patient-specific anatomical model of the liver including a liver parenchyma, at least one tumor, a hepatic vein, a portal vein, and at least one artery by segmenting the liver parenchyma, the at least one tumor, the hepatic vein, the portal vein, and the at least one artery in the medical image; simulating blood flow in vessels and porous regions of the target organ based on the patient-specific anatomical model by: calculating 3D blood flow and inlet pressures in the hepatic vein over a plurality of time steps using computational fluid dynamics (CFD) simulation, calculating portal vein and artery upstream pressures over the plurality of time steps based on the blood flow and the inlet pressures in the hepatic vein, and calculating 3D blood flow in the portal vein and the at least one artery over the plurality of time steps based on the portal vein upstream pressures using CFD simulation; simulating heat diffusion due to ablation based on a virtual ablation probe position and operating parameters and the simulated blood flow in the vessels and porous regions of the target organ considering both cooling effects from the blood flow in the vessels and the porous tissue blood perfusion by calculating, for each of a plurality of points in the patient-specific anatomical model, a temperature at each of the plurality of time steps using a first bio-heat equation having a first cooling term if the point belongs to a vessel or an artery, and a second bio-heat equation having a second cooling term if the point belongs to a porous medium; simulating cellular necrosis in the target organ based on the simulated heat diffusion; and generating a patient-specific visualization of a necrosis region in the anatomical model resulting from the simulation of heat diffusion due to ablation and the simulation of the cellular necrosis in the target organ.