1. To identify biomarkers of radiation-induced intestinal injury;
2. To develop a predictive model for radiation-induced intestinal injury.

1. Enroll eligible patients and obtain written informed consent.

2. Collect clinical data.

3. Sample collection and biomarker assessment: Peripheral blood, urine, and stool samples will be collected from patients before the initiation of radiotherapy and after the start of radiotherapy, followed by multi-omics analyses.

4. Patient follow-up: Patients will be followed during radiotherapy, within 1 month after completion of treatment, and every 3 months thereafter; after 1 year, follow-up will be conducted every 6 months. Patients' symptoms, laboratory tests, and examination results will be recorded. Radiation-induced intestinal injury and its grading will be assessed according to the Radiation Therapy Oncology Group (RTOG) criteria. In addition, treatments and outcomes after the occurrence of radiation-induced intestinal injury will be documented.

   The primary endpoint is radiation-induced intestinal injury, and the secondary endpoint is overall survival.

5. Data integration: Clinical data, previous research findings, and biomarkers measured from patient samples will be integrated to identify biomarkers of radiation-induced intestinal injury and to develop a predictive model using bioinformatics approaches.

Inclusion Criteria:

1. Abdominal radiotherapy dose ≥45 Gy;
2. Age ≥18 years;
3. Karnofsky Performance Status (KPS) >60;
4. Expected survival >6 months.

Exclusion Criteria:

1. Prior history of abdominal radiotherapy;
2. Active intestinal infection;
3. Intestinal inflammatory diseases due to other causes;
4. Inability to provide biological samples.

Patients with malignant tumors undergoing abdominal radiotherapy that may involve the intestine