Breast-conserving treatment is a combination of surgery as the mainstay and radiotherapy as the base supplemented by chemotherapy. Radiation therapy after breast-conserving surgery has been the classic mode of breast-conserving treatment. According to statistics, whole-breast radiotherapy after breast-conserving surgery can reduce the 10-year local recurrence rate from 29.2% to 10% after breast-conserving surgery for early-stage breast cancer. Therefore, in principle, all patients undergoing breast-conserving surgery should undergo postoperative radiotherapy as long as there is no contraindication to radiotherapy. The following is a discussion and summary of several hot issues of postoperative radiotherapy for breast-conserving cancer: I. Timing of radiotherapy Postoperative radiotherapy for patients without adjuvant chemotherapy is recommended to be performed within 8 weeks after surgery. Because of the dynamic changes in the volume of the operative cavity in the early postoperative period, especially for patients containing seroma, radiotherapy is not recommended to be started within 4 weeks after surgery. Patients receiving adjuvant chemotherapy should be started within 2 to 4 weeks after the last chemotherapy. In China, alternating chemotherapy and radiotherapy (sandwich treatment) is more commonly used: radiotherapy is inserted in between chemotherapy, 2 cycles of chemotherapy are given after surgery, and radiotherapy is given after 1 to 2 weeks of rest, and chemotherapy is continued after 1 to 2 weeks of rest after the completion of radiotherapy. However, this treatment method lacks evidence-based medical evidence and is not recommended. Bed of tumor dosing Bed of tumor dosing is a further dosing of the tumor bed on top of whole breast irradiation, because most local recurrences are near the tumor bed. Studies have shown that bed-of-tumor dose irradiation can significantly reduce the local recurrence rate (0.9%-8.8%). Therefore, tumor bed dose supplementation is necessary after whole breast radiotherapy, and electron wire dose supplementation is the most common way at present. Conventional segmentation (50.0Gy/25 times) has limited the development of breast-conserving treatment due to the long radiotherapy time and high cost. “Large fractionated radiotherapy (42.5Gy/16 sessions) is aimed at shortening the total course of treatment or reducing the number of irradiation sessions, and is more favorable for elderly patients and patients with limited transportation access to breast-conserving treatment. Currently, it is suitable for early-stage breast cancer patients aged 50 years or older who are undergoing breast-conserving surgery. Three-dimensional conformal radiotherapy and three-dimensional intensity modulated radiotherapy Three-dimensional conformal radiotherapy (3D-CRT) is an irradiation technique that can make the dose distribution in the high-dose area consistent with the actual shape of the target area in the three-dimensional direction. It uses CT images to reconstruct the tumor structure in three dimensions. By setting a series of different irradiation fields in different directions and using conformal lead blocking that is consistent with the shape of the lesion, the shape of the high-dose area distribution is consistent with the shape of the target area in the three-dimensional direction, and at the same time, the exposure of the normal tissue around the lesion is reduced. Three-dimensional intensity-modulated radiotherapy (IMRT) is to adjust the beam intensity for the three-dimensional shape of the target area and the specific anatomical relationship between the vital organs and the target area under the condition that the radiation field at each location is consistent with the shape of the target area, and the dose distribution within a single radiation field is not uniform, but the dose distribution within the entire volume of the target area is more uniform than that of three-dimensional conformal radiotherapy treatment. Several studies have confirmed that 3D intensity-modulated radiotherapy has significant advantages over conventional radiotherapy and 3D conformal radiotherapy in that the dose to the tumor and the dose to the vital organs can be precisely controlled. Numerous studies have shown that 3D intensity-modulated radiotherapy can significantly improve tumor control rates and reduce complications.