Breast cancer is one of the most common malignant tumors in women, and its incidence is increasing year by year. In Europe and the United States, breast cancer accounts for 25-30% of all malignant tumors in women, and statistics from the late 20th century show that about 1.3 million people are diagnosed with breast cancer and 400,000 die from the disease each year worldwide. The incidence rate of breast cancer in China is increasing year by year, and it has become the second most common cancer among women, and has risen to the first place in some big cities. With the deepening understanding of the biological characteristics of breast cancer, people gradually realize that breast cancer is a systemic disease, and thus the classical radical breast cancer surgery is still only a local treatment, but it brings great harm to the physical and mental health of patients. Breast-conserving treatment is a new treatment concept that has little adverse effect on the physical and mental health of patients. There is no statistically significant difference between breast-conserving treatment and radical surgery in terms of recurrence and survival rates, while breast-conserving treatment allows women to keep their bodies in good shape. Therefore, breast-conserving treatment has become the main treatment for early-stage breast cancer in Western countries. However, the recurrence rate after breast-conserving surgery without radiotherapy is over 60%, while the recurrence rate after breast-conserving surgery with radiotherapy is reduced to about 9%. Therefore, radiotherapy has become an essential treatment after breast-conserving surgery. However, due to the biological and physical characteristics of radiation, while killing tumor cells, it inevitably causes certain damage to normal tissue cells in the irradiation area, such as skin reaction: redness, dry peeling, wet peeling, ulceration, etc.; mucous membrane reaction: congestion, erosion, ulceration, co-infection, etc.; subcutaneous tissue: tissue fibrosis, lymphatic flow obstruction, swelling of limbs, etc. Pulmonary reactions: such as coughing, chest tightness, wheezing and other manifestations of radioactive pneumonia; cardiac reactions: such as chest pain, cardiac insufficiency and other manifestations of radioactive cardiac inflammation. These reactions obviously reduce patients’ quality of life and affect their treatment tolerance. As an emerging radiation therapy technology, IMRT, i.e. Intensity Modulated Radiation Therapy, can effectively reduce the volume and dose of irradiation to the endangered organs and reduce the chance of side effects through inverse calculation and plan optimization, resulting in better conformality of radiation therapy and more uniform dose distribution in the target area. Currently, breast cancer radiotherapy technology is undergoing a change from conventional simulation and two-dimensional planning to CT simulation, three-dimensional and intensity-modulated treatment. With the application of computers and spiral CT in the field of radiotherapy, conformal radiotherapy and intensity-modulated radiotherapy can make the shape of the dose distribution in the high-dose area consistent with the actual shape of the target area at the three-dimensional level. The dose intensity within the target area is adjustable, thus increasing the irradiation dose to the tumor without reducing or increasing the normal tissue damage and improving the local control rate and/or patient’s quality of life, which not only achieves better results, but also significantly reduces the incidence of complications. However, conventional half-beam radiation therapy for breast cancer has many disadvantages such as high irradiation of normal tissues, non-uniform dose and many complications. The use of conformal intensity modulated radiotherapy has been shown to overcome these problems. IMRT has also reduced the incidence of acute dermatitis (a common complication after radiotherapy, occurring in up to 50% of patients). . Conformal intensity-modulated radiation therapy applied to breast cancer treatment has reduced skin reactions and cardiopulmonary toxicity while increasing the target dose, better ensuring its cosmetic effects and improving the long-term quality of life of patients. Since 2005, our center has carried out conformal intensity modulated radiotherapy after breast-conserving surgery and radical surgery for early-stage breast cancer, which has achieved excellent results and significantly improved the treatment effect of breast cancer and patients’ quality of life, and has been widely praised by patients.