## 1 Introduction  
Liver cancer is one of the leading causes of death worldwide [1]. The most common type of liver cancer is hepatocellular carcinoma, which is mainly caused by cirrhosis due to the Hepatitis B virus (HBV), Hepatitis C virus (HCV), alcohol, and tobacco. Over 75% of liver cancer cases are attributable to persistent viral infections with either HBV or HCV. Cirrhosis infection with HBV or HCV is more likely to develop into hepatocellular carcinoma [2; 3; 4; 5]. In addition to these two major contributors, excessive alcohol consumption is a significant risk factor of cirrhosis that will later develop into hepatocellular carcinoma as well [6; 7; 8]. Current treatments for liver cancer include surgery (partial hepatectomy or liver transplant), tumor ablation, radiation therapy, chemotherapy, targeted therapy, and hepatic artery embolization. Surgery is the most commonly used method of treating early-stage liver cancer; however, it is limited to patients with smaller tumors and without other severe diseases. For patients who are not suitable for surgery, the following treatments may be better options. In tumor ablation, a needle or probe is inserted into the tumor through the skin; then, a high-frequency current, concentrated alcohol, or microwaves are delivered to the liver tumors to destroy them without removing them. In radiation therapy, high-energy rays are used to kill cancer; however, the radiation can easily damage healthy liver tissue as well. In chemotherapy, anti-cancer drugs are injected into a vein, where they enter the bloodstream and reach all areas of the body. In contrast, targeted therapy flags specific genes or proteins and prevents the growth of cancer cells with minimum side effects. In hepatic artery embolization, small beads are injected to block a branch of the hepatic artery and thereby reduce the blood flow towards cancer cells; however, it has some clinical limitations. First, its flow direction is difficult to control, and the beads may also travel to normal blood vessels and healthy cells. Furthermore, the embolization effects last for only a limited period, so multiple treatments are required. [PERSON] et al. studied the effects of vascular occlusion in mouse tumors by applying D-shaped metal clamps to induce regrowth delay. Results showed that after 18 h of clamping, no tumors regrew within 23 days. It was found that a clamping period exceeding 24 h was necessary to achieve complete eradication of tumor cells [9]. [PERSON] et al. performed transcatheter hepatic artery embolization in 120 patients with unresectable hepatoma. Based on [PERSON]'s criteria, the therapeutic effects of hepatic artery embolization were rated as 0-B (favorable objective changes without subjective benefit) or better in 96% of the total cases and as 1-B (observed tumor regression unequivocally) or better in 75% of the total cases [10; 11]. [PERSON] et al. evaluated the clinical effects of the Amplatzer vascular plug, an embolization device for congenital heart disease made by Abbott Vascular (Santa Clara, CA, USA). Results showed that 94% of the patients had complete vessel occlusion within ten minutes [12]. These previous studies have demonstrated that tumor regrowth can indeed be reduced by cutting the blood supply to cancer cells. Therefore, we propose a novel nitinol \"spherical occlusion device\" for future cancer treatment options. This device, the first of its kind in the world, also represents the first \"spherical\" variation or transformation from traditional intravascular stents with a cylindrical shape. The spherical occlusion device is crimped inside a catheter for delivery to the lesion site and deployed at the upstream location of the hepatic artery to cut off the blood supply. It can stay inside the body for months as needed and be retrieved by catheter when the task is completed. Furthermore, it can carry chemotherapy and radioactive drugs directly to the lesion site and treat cancers more effectively.