Worldwide, the incidence of cancer is greatest in China. Tumor screening is effective to achieve early diagnosis, improve prognosis, increase the quality of life, and reduce mortality among cancer patients. Positron emission tomography/computed tomography (PET/CT) imaging provides metabolic data to support initial staging, treatment planning, and response evaluation in tumor screening, as well as tumor follow-up. The progressive integration of PET/CT imaging in radiotherapy has its basic principle in the biological heterogeneity of inter- and intra-tumor malignant lesions, and the radiation dose is required to be adjusted to achieve effective local tumor control among cancer patients. In addition, PET/CT imaging provides data on the biological features of tumor lesions, such as metabolism, hypoxia, and proliferation, which is useful to identify radiation-resistant regions and optimize treatment plans. These data are effective to reduce the uncertainty and variability in the anatomic description of tumor sites. This review summarizes the application of PET/CT imaging in common tumors.

The combination of conventional single-photon emission computed tomography (SPECT) and computed tomography (CT) may display the morphological changes of lesions and distribution of imaging agents, which is effective to improve the imaging sensitivity and specificity of tumors and non-tumor diseases. SPECT/CT is feasible to analyze the anatomical structure and metabolic status through displaying multi-site lesions with single imaging, thereby improving differential diagnosis and diagnostic accuracy of diseases. In addition, the novel mixed SPECT/CT device shortens the duration of image acquisition and provides precise attenuation correction and fusion imaging, which provides a scientific basis for rational selection of treatment regimens in clinical practice. This review describes the advances in clinical application of SPECT/CT.