Radiotherapy is a local treatment for tumors and plays a major role in tumor treatment. Many patients have the same question, that is, why do they need radiotherapy after the surgery is already successful, and what exactly is the role of radiotherapy? The following is a brief introduction to this problem. 1, prevention of tumor recurrence: Because the growth of tumor is mainly manifested as infiltrative growth like tree roots, there are often some subclinical lesions that need microscope to be found outside of the visible tumor, these lesions are sometimes difficult to be removed cleanly by surgery, and then become the root cause of recurrence. There are also some tumor cells that adhere to the surgeon’s gloves or surgical instruments during surgery and then implant on the surgical wound or incision, laying the groundwork for future recurrence. Post-operative radiotherapy can eliminate these microscopic lesions and reduce future recurrence, for example, for patients with mid-stage and advanced breast cancer and rectal cancer. 2.Cure tumors: Many tumors, such as nasopharyngeal carcinoma, because they are located at the base of the skull, surgery is not easy to reach the ideal treatment effect, and it is difficult to remove them completely, plus they are more sensitive to radiotherapy, so radiotherapy can achieve the same effect as surgery, while avoiding the destructive nature of surgery. 3. Combine with surgery to preserve organs: Currently, foreign countries have widely chosen “minor surgery and major radiotherapy” to treat certain tumors in order to preserve the function of diseased organs. For example, breast cancer is treated by local enlargement of the tumor and breast preservation surgery; most patients with osteosarcoma of the limb do not need to choose amputation and preserve the limb, and postoperative prophylactic radiotherapy. The above is the introduction of the role of radiotherapy, I hope it will be helpful to you. We would like to remind you that tumors must be treated in time, and you should choose the treatment method suitable for your condition in order to achieve the best treatment effect.