PET – CT- which is a method that increases success in the fight against cancer to identify cancerous tissues, treatment planning, and evaluation of the process, is considered as one of the most important technologies for many patients to have a healthy life. Positron emission tomography (PET-CT) technology, combined with computed tomography (CT), is an important technology medical imaging method that enables the diagnosis of many diseases. PET / CT is widely used in the diagnosis and staging of cancer. In addition, its effectiveness is utilized in the diagnosis of “undiagnosed diseases” such as fever of unknown origin, presence of infection foci, detection of living tissue in cardiac patients, and differentiation of Alzheimer’s and dementia. In particular, all stages are carried out with a PET / CT device for the initial diagnosis, staging, determination of the prevalence, and correct treatment plan. A road map of cancer treatment with PET / CT makes a significant contribution to the fight against the disease.