Radiotherapy is a cornerstone of cancer management that utilizes ionizing radiation energy to destroy cancer cells. Radiotherapy is also known as radiation therapy. By directing ionizing radiation at the cancerous area, it damages the DNA of cancer cells, impairing their ability to reproduce and leading to cell death. Radiotherapy can be delivered externally, through external beam radiation, or internally, via brachytherapy where radioactive sources are placed inside or near the tumor. It can be used as a standalone treatment, or in conjunction with surgery, chemotherapy, and other therapies to enhance treatment outcomes. The precision and effectiveness of radiotherapy have significantly improved with advances in medical imaging and radiation delivery techniques, allowing for targeted treatment that minimizes damage to surrounding healthy tissues. Its application varies widely across different types of cancer, providing a critical therapeutic option for both curative and palliative care.