The objective of the study is to constrcut a noninvasive approach 124I-18B10(10L) PET/CT to detect the CLDN18.2 expression of tumor lesions in patients with gastrointestinal tumors and to identify patients benefiting from CLDN18.2 targeting treatment.

Inclusion Criteria:

• 1. Aged >18 years old; ECOG 0 or 1;
• 2. Patients with Gastrointestinal tumors;
• 3. Has at least one measurable target lesion according to Response Evaluation Criteria in Solid Tumors (RECIST V1.1);
• 4. life expectancy >=12 weeks.

Exclusion Criteria:

• 1. Significant hepatic or renal dysfunction;
• 2. Is pregnant or ready to pregnant;
• 3. Cannot keep their states for half an hour;
• 4. Refusal to join the clinical study;
• 5. Suffering from claustrophobia or other mental diseases;
• 6. Any other situation that researchers think it is not suitable to participate in the experiment.