Radiotherapy (radiation therapy) is one of the basic treatment methods for cancer, where high energy rays are used for treatment. The basic mechanism of action of ionizing radiation used in radiotherapy is to destroy tumor DNA and prevent tumor cells from multiplying in the first step. Genetically damaged cells die after a few splits. Ionizing rays also cause DNA damage in normal cells in normal human tissues, but normal cells have the ability to repair this damage when the tumor cells can not get rid of it. 
Radiotherapy (radiation therapy) is not used only for complaints of the patient in the last stages of the disease, contrary to popular belief in the society. Radiotherapy is an effective treatment modality, which is the earliest stage of almost all organ tumors that may come to mind. Depending on the condition of the patient and the patient, it may be used together with other treatment modalities, either sequentially or as a stand-alone treatment option.

Radiotherapy (radiation therapy) is generally used for 4 purposes:

Preoperative radiotherapy (Neoadjuvan): In some tumors, especially lung and rectum tumors, radiotherapy is applied before surgery to reduce the tumor and reduce the surgical burden. Thus, for example, in the bowel tumors, it is possible to get rid of the abdomen which is called colostomy if the abdomen is out of the skin, or to take only one lobe instead of taking the entire lung in lung tumors.
Post-operative radiotherapy (adjuvant): Radiotherapy is performed after surgery in many tumor types, especially breast tumors. The aim is to eliminate the possible tumor cells that may have remained in the disease area and prevent the disease from recurring in the following years.
Radiotherapy alone (Primer): Larynx tumor, Prostate cancer, etc. Radiotherapy can be a treatment option alone and it gives good results as well as some advantages. For example, the surgical method is also an option in tumors of the voice-tails, and both methods achieve successful results at similar times, but at the same time as the radiotherapy, the voice of the patient is maintained at a much higher level than the surgical method.
Radiotherapy for complaints (Palliative): Radiotherapy is an important treatment option in metastases seen in advanced stage patients. Radiotherapy is the most valuable choice, especially in brain and bone metastases. The aim here is to prevent complaints such as pain, bleeding and shortness of breath caused by metastasis as well as to prevent much more severe conditions such as pathological fractures, paralysis, unconsciousness.