As one of the main treatments for all cancers, radiotherapy will inevitably cause adverse reactions during treatment; although these adverse reactions will occur when receiving radiotherapy, the effect of radiotherapy for breast cancer is very significant, which can effectively control the spread of cancer cells and prevent the disease from continuing to deteriorate. The early local adverse reactions of breast cancer radiotherapy will appear within 2 – 3 weeks of radiotherapy; the skin in the treatment area will become red, dry, tingling and itchy, and as the treatment progresses, the skin will become moist and blistered, so the radiotherapy site should be exposed to the air as much as possible during the treatment, which is conducive to skin recovery; local skin redness and pain, which can spread to the irradiated field, often resolves after 1 – 2 weeks; the last thing physicians and patients want is the possibility of lymphedema after 6 – 7 weeks of radiotherapy, resulting in persistent edema of the upper extremities after surgery (mostly seen in irradiated axillary lymph node area patients). Radiation therapy for breast cancer can also cause myocardial damage, coronary artery disease, or costochondritis, leading to spontaneous fractures, joint stiffness, and pulmonary fibrosis. In addition, most patients’ breasts look and feel the same as before radiotherapy, but a few may become harder, larger or smaller, or the skin becomes more sensitive or numb. With the clarification of the efficacy of breast-conserving surgery plus radiotherapy for early-stage breast cancer and the progress of comprehensive treatment for progressive breast cancer, the role of radiotherapy in the treatment of breast cancer can no longer be ignored. The average survival period of breast cancer patients is longer, and the quality of survival and efficacy are increasingly emphasized. Currently, the advantages of conformal intensity-modulated radiotherapy for breast cancer are mainly reflected in the following four points: (1) Uniform dose distribution in the target area: The tangential field plus wedge plate technique is commonly used to set up the field after breast-conserving surgery for early and mid-stage breast cancer, but this technique has the problem of uneven dose distribution, especially in the upper, lower and bilateral bases of the breast and under the nipple, where there are inevitably high dose areas, and the highest prescribed dose can reach 115% -120%. –The highest prescribed dose can reach 115% -120%, and the skin reaction and fibrosis in the above mentioned areas are obvious after radiotherapy, which seriously affects the cosmetic effect. Intensity-modulated radiotherapy is a precise radiotherapy technique that makes 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, and the dose intensity in the target area is adjustable, thus reducing the dose to normal tissues and reducing normal tissue damage while achieving the same dose to the target area. (2) Reduced dose to important organs: The breast is a highly irregular shaped organ, and it is difficult to achieve uniform dose in the target area during conventional radiotherapy. In the case of left-sided breast cancer, complications in the left anterior part of the heart, coronary artery and pericardium are increased. In contrast, techniques such as conformal intensity modulated radiotherapy can reduce the dose of exposure to vital organs. However, in cases where radical breast cancer resection has been performed, the postoperative chest wall thickness is only 1-1.5 CM, and it is questionable whether the application of conformal intensity modulated radiotherapy to the chest wall is better than conventional electron beam irradiation, especially in reducing non-lethal radiation complications to lung tissue. (3) Reduction of related organ complications: Clinical studies of axillary lymph node dissection have shown that radiotherapy to axillary lymph nodes can cause many long-term adverse effects, such as upper arm edema, sensory numbness, and limitation of upper limb movement and muscle strength. Internal breast lymphatic chain irradiation has been associated with reduced tolerance to chemotherapy and high mortality rates due to myocardial infarction or cardiovascular disease. Conformal intensity-modulated radiotherapy for breast cancer can avoid direct irradiation of intolerable tissues or lower the dose of irradiation of intolerable tissues, especially for radical radiotherapy after breast-conserving surgery for left-sided breast cancer. (4) Shortened radiotherapy time: 67% – 86% of patients with breast-conserving surgery have recurrence sites around the tumor bed. Conventional whole breast irradiation is prescribed at a total dose of about 5000 CGy and generally takes up to 5–7 weeks. The results of several studies suggest that accelerated partial breast irradiation (including only the tumor bed and surrounding tissues) after breast-conserving surgery for early-stage breast cancer can achieve the same therapeutic efficacy as whole-breast radiotherapy, with the advantages of shorter radiotherapy time and less toxic side effects; accelerated partial breast irradiation can be completed within 1–2 weeks, significantly shortening the radiotherapy time. The accelerated partial breast irradiation can be completed within 1 – 2 weeks, significantly shortening the radiotherapy time. In recent years, the results of multicenter prospective clinical studies and the application of evidence-based medical research results have led to a deeper understanding of the biological behavior of breast cancer and the factors affecting the healing process. Modern diagnostic imaging techniques, new radiotherapy equipment and three-dimensional treatment planning systems have been developed to locate the target area and key organs more accurately and to design and achieve the ideal dose distribution; breast cancer radiotherapy target areas, indications and radiotherapy techniques are being continuously developed and improved.