Two major topics were covered in this chapter. The first was to explore a method of establishing a rabbit model of SVCS by injecting VX2 tumor cell suspension transcutaneously under ultrasound guidance, and to observe the radiotherapeutic effects by SVC Doppler flow changes. The establishment of this model would offer an experimental evidence for better diagnosis, treatment and follow-up observation of SVCS. The second was to investigate the evolution of the SVC Doppler flow changes in patients with SVCS and its value in assessing clinical therapeutic effects in these patients. An animal SVC obstruction model would be of use in further studies directed at optimizing the therapeutic strategies for original tumors causing SVC syndrome in patients, yet no detailed information about the establishment of an animal SVC obstruction (SVCO) model can be found in the literature. It has been reported that VX2 tumor cell could be successfully inoculated into multiple organs to induce malignant tumors in rabbits (De Crespigny et al, 1999; Goldberg et al, 1999; Ishida et al, 2000), and various imaging modalities has been adopted to assess the effect of this inoculation (Kim et al, 2000; Liu et al, 2001). We hypothesize that a rabbit model with SVCO could be established by inoculating VX2 tumors cells into the areas around the SVC. Superior vena cava syndrome (SVCS) is a clinical expression of obstruction of blood flow through the SVC, and more than 80% cases are caused by malignant tumors. Though contrast-enhanced spiral or multi-slice CT is now able to identify accurately the site of occlusion or stenosis, it has been greatly limited by its high cost and radiation and thus is not appropriate for follow-up observations. In contrast, ultrasound is safe, reproducible, and relatively inexpensive. Doppler ultrasonography has been successfully used to assess the rabbit SVC obstruction model. We hypothesize that Doppler flow patterns of SVC could be applied for assessing the severity of SVCS and its therapeutic effects.