China is a high incidence area for liver cancer, with about 110,000 people dying from liver cancer every year, accounting for about 45% of liver cancer deaths in the world. Liver cancer is also one of the malignant tumors that are difficult to treat. Although the surgical treatment of liver cancer has made some breakthroughs in recent years, there are still few early stage cases that can be surgically removed. Because the liver was thought to be resistant to radiation in the past, the positioning was difficult to be accurate under ordinary simulators, and conventional radiotherapy would cause damage to the liver and important organs around the liver, so radiation therapy for liver cancer was limited. As a result, radiotherapy was rarely used for the radical treatment of liver cancer in the past. Recently, research has confirmed that liver cancer is a radiation-sensitive tumor, and the latest American Comprehensive Cancer Network strongly recommends radiation therapy for liver cancer. In fact, the real limitation of radiation therapy for liver cancer is not that liver cancer is insensitive to radiation, but that the traditional irradiation methods in the past were unable to precisely target and effectively protect the normal liver and adjacent organs. As a result, the irradiated area of normal liver is too large and the adjacent organs are exposed to almost the same dose as the tumor, resulting in radiation damage. Three-dimensional conformal radiotherapy technique, due to its precise positioning, provides excellent protection to the normal liver and surrounding vital organs, allowing the tumor to receive high doses of irradiation without causing significant radiation damage to the liver and adjacent organs. It is believed that 3D conformal radiotherapy using the conventional segmentation method, the tumor area can receive up to 70Gy irradiation dose which is still safe for normal liver cells. With the clinical application of three-dimensional conformal and intensity-modulated radiotherapy techniques, a new situation has been created for radiation therapy of liver cancer. The main reason for the unsatisfactory radiotherapy of liver cancer in the past was directly related to the insufficient irradiation dose. Clinical observation shows that the rates of complete and partial remission for those with irradiation dose above 50GY are 11.4% and 61.4% respectively, while those with irradiation dose less than 50GY are only 0% and 46.7%. The application of three-dimensional conformal radiotherapy technology can irradiate the tumor with sufficient dose, thus significantly improving the radiation treatment effect of liver cancer.