This publication is a resource for specialists in nuclear medicine and radiation oncology on the coupling of positron emission tomography and X ray computed tomography (PET/CT) to more accurately identify cancer cells within the body. Besides, although radiation therapy plays an important role in cancer treatment as an effective non-invasive therapy, damage to normal cells in the vicinity of tumour cells may be detrimental to the patient’s health and recovery. The joint use of PET and CT provides superior imaging of the existing disease and, therefore, promises to minimize adverse effects of radiation therapy. By more precisely marking the presence of cancerous cells, thereby facilitating more precise irradiation, it also enables an increase in the dose of radiation therapy delivered to the malignant cells, which leads to better tumour control and improved survival of patients