Radiotherapy is a type of cancer treatment that uses high-energy radiation to kill or damage cancer cells. It can be used alone, after surgery, or in combination with other treatments such as chemotherapy. The goal of radiotherapy is to target and destroy cancerous tissue while minimizing harm to healthy tissues. There are two main types of radiotherapy: external beam radiation therapy (EBRT), which uses a machine outside the body to direct radiation at the tumor, and internal radiation therapy (brachytherapy or IORT), where radioactive material is placed inside the body near the cancer cells.