1. Identify benign and malignant tumors or lesions: As we all know, identifying benign and malignant tumors is very important, which is not only related to the treatment plan, but also directly affects the patient’s prognosis. For example, if a patient has a single nodule in the lungs and the metabolic activity of the nodule is not high after PET/CT examination, it suggests that the possibility of benign lesions is high and the choice of surgery should be cautious; on the contrary, if the metabolic activity of the nodule is increased, it suggests that the possibility of malignant, and active treatment measures should be taken, including surgery. Tumor staging: Tumor staging is an important basis for deciding the treatment plan of patients, PET/CT whole body imaging of patients, a PET/CT whole body imaging can provide the information of whether there is any metastasis in various organs of the whole body, such as brain, lungs, lymph nodes, liver, adrenal glands and bones, which is conducive to the accurate clinical staging of various tumors, such as lung, breast, colon, ovary, and lymphoma, etc. Take the diagnosis of lymph node metastasis as an example, it can be used to diagnose lymph node metastasis. Taking the diagnosis of lymph node metastasis as an example, PET/CT is more accurate, because CT or MRI regards enlarged lymph nodes (>1cm) as metastasis, in which there is no lack of enlarged lymph nodes due to chronic inflammation, or misjudges normal-sized lymph nodes that have been invaded by tumor tissues, whereas PET is more accurate in determining whether metastasis occurs according to the metabolic activity of lymph nodes, rather than considering only the size of the lesion. Evaluation of therapeutic efficacy: Due to the high sensitivity of PET/CT and its functional metabolic imaging, it is more accurate and sensitive in judging the therapeutic efficacy of radiotherapy and chemotherapy, which is helpful in guiding clinicians to adjust the treatment plan in time. 4, identify necrosis, fibrosis and residual or recurrent tumors after treatment: PET/CT can identify necrosis, fibrosis and residual or recurrent tumors after chemotherapy, radiotherapy and surgery, which is difficult to be done by other imaging means. 5, help to make tumor radiotherapy plan: PET/CT can help radiotherapists outline a more reasonable biological target area and help to make radiotherapy plan. 6.Finding of tumor primary foci: Patients who have clear tumor metastases can further find the primary tumor foci through PET/CT examination.