1.Clinical staging and re-staging of tumors, evaluation of the extent of tumor invasion, metastases, malignancy, etc., to provide a basis for treatment decision. 2.Monitoring of tumor recurrence after radiotherapy or surgery. 3.Assist in the differentiation of benign and malignant lesions. 4.Monitoring and evaluation of the efficacy of tumor radiotherapy and chemotherapy in order to adjust the treatment plan in a timely manner. 5.Accurate description of tumor lesions and their metastases to assist in determining radiotherapy target areas. 6.For unexplained lymph node enlargement, increased serum tumor markers, or unexplained fever, etc., search for the tumor primary lesion. 7.To judge the prognosis of tumor patients.