Radiotherapy is a treatment method that uses high-energy rays to target and destroy cancer cells. This treatment is applied to a limited area and affects only the cancer cells within the treatment region. It can be administered before surgery to shrink a tumor (neoadjuvant), after surgery to eliminate remaining cancer cells (adjuvant), or as a primary treatment on its own. Especially in cases of regionally advanced cancer unsuitable for surgery but without distant metastasis, radiotherapy is generally considered one of the main treatment options, often in conjunction with chemotherapy. Furthermore, in advanced-stage cancer patients, it is also used as a palliative treatment to alleviate symptoms such as pain or shortness of breath.