This is an open-label positron emission tomography/computed tomography (PET/CT) study to investigate the clinical predictive value of 68Ga-ICAM-1pep in metastatic cancer patients receiving radiotherapy. A single dose of 2.96 MBq/kg body weight of 68Ga-ICAM-1pep will be injected intravenously. The visual and semiquantitative methods will be used to assess the PET/CT images.

Radiotherapy has a systemic inhibitory effect on non-irradiated lesions (abscopal effect) in addition to local antitumor effects, and currently no biomarkers are used for the prediction of the abscopal effect of radiotherapy in standard clinical practice. Our recent preclinical studies identified ICAM-1 as a potential predictive biomarker for the radiotherapy-induced abscopal effect. In this clinical trial, we aim to investigate whether the ICAM-1-targeting radiotracer 68Ga-ICAM-1pep could be used for PET imaging of tumor responses to radiotherapy in cancer patients. PET/CT imaging of 68Ga-ICAM-1pep will be performed in patients before and after radiotherapy.

Inclusion Criteria:

1. 18-80 years old;
2. ECOG score 0 or 1 point;
3. Patients with suspected or confirmed lung cancer, esophagus cancer, cervical cancer or other cancers who are suggested by the clinicians to conduct PET/CT imaging for tumor diagnosis or staging.

Exclusion Criteria:

1. Pregnant or nursing;
2. Severe hepatic or renal dysfunction;
3. Low WBC (less than 3 x 10^9/L);
4. Unable to comply with the PET/CT imaging procedures.