Radiation therapy has been used for breast cancer for 100 years, but in the early years, it was only used as postoperative complementary treatment or palliative treatment for advanced and recurrent cases. It was not until 1941 when Mcwhirter first used simple mastectomy plus radiotherapy to replace radical surgery that radiotherapy took a step forward in the treatment of breast cancer. In recent years, with the improvement of radiotherapy equipment and technology, as well as the progress of radiobiological research, it is possible to obtain higher doses locally with less damage to the surrounding normal tissues, and the radiotherapy effect is obviously improved. With the development of screening technology and the popularization of knowledge, more and more breast cancers are detected at an early stage. In the past, the treatment for breast cancer was mainly radical surgery, but in recent years, breast-conserving treatment has gradually become the standard treatment for early-stage breast cancer, because while preserving the function of the patient’s breast, several clinical trials have confirmed that there is no statistical difference in the local recurrence rate and survival of breast-conserving treatment compared with those of radical surgery patients. The so-called breast-conserving treatment usually includes breast-conserving surgery (segmental, quadrant or swelling excision with axillary lymph node dissection) and postoperative radiotherapy (whole breast irradiation plus incremental irradiation of the tumor bed and irradiation of the regional lymphatic drainage area). 1.Post-operative radiation therapy after breast-conserving surgery 1.Immunization scope If the axillary lymph nodes are not cleared, the irradiation scope should include the breast, chest wall, ipsilateral axilla and supraclavicular lymph nodes. For patients whose axillary lymph nodes have been cleared, the scope of irradiation depends on the metastasis of the axillary lymph nodes. For patients with no axillary lymph node metastasis or 1 to 3 metastatic lymph nodes, only the breast and chest wall should be irradiated. For axillary lymph nodes with ≥4 metastases, the breast, chest wall, supraclavicular and parietal axillary lymph nodes should be irradiated. If the axillary lymph nodes are only sampled in a low position, all axillary lymph nodes should be irradiated if they have metastases. The extent of additional dose irradiation should be determined by the metal markers placed intraoperatively or 3 cm around the surgical scar; the area of internal breast lymphatic drainage is highly controversial and radiation therapy is not recommended. Radiation therapy is not recommended even if the tumor is located in the medial quadrant, unless imaging or anterior lymph nodes show positive internal breast lymph nodes. If radiation therapy is performed in the internal breast area, it is also recommended that the irradiation area should only cover the 1st to 3rd intercostal space. If the primary tumor has been completely removed, the additional irradiation dose for the primary lesion is 10 Gy; if the primary tumor is not completely removed, the additional irradiation dose is 15-20 Gy. The irradiation for the regional lymphatic drainage area is a preventive dose: 50 Gy for 5-5.5 weeks. weeks.