A special treatment procedure that utilizes the irradiation of a target with sealed radioactive sources placed at short distances from the target and inside the patient's body. Typically, the sources are implanted in the target tissue directly (interstitial brachytherapy) or are placed at distances of the order of a few mm from the target tissue, in body cavities such as the uterus, mouth, etc. (intracavitary brachytherapy)