Radiation therapy is one of the main means for treating malignant tumor, during which radioactive lung injury is inevitable. Currently there is nearly no effective clinical treatment for late post-radiotherapy pulmonary fibrosis. This study intends to carry out an open, single-center, non-randomized phase I clinical trial. During the treatment, the local lesions will be fully lavaged, and then clinical grade umbilical cord mesenchymal stem cells (MSCs) will be injected directly into the lesion by fiberoptic bronchoscopy. After six-month observation, the investigators will initially evaluate the safety and effectiveness of the treatment by measuring two key indicators-the CT density histogram and the patients' self-evaluation, and one secondary indicator-the changes of TGF-β1 contents, both before and after the treatment. Meanwhile, the investigators will make a preliminary discuss about the possible immunomodulatory effects of the umbilical cord MSCs.

Inclusion Criteria:

1. Male or female, 18-70 years old.
2. Subjects with a clear history of malignancy.
3. Subjects with a clear history of chest radiation therapy at least 3 months earlier.
4. Subjects diagnosed as chronic phase of radiation-induced pneumonitis or radiation-induced pulmonary fibrosis stage (see Annex 3 for diagnosis).
5. Subjects signed informed consent.

Exclusion Criteria:

1. Women of childbearing age at the stage of pregnancy or lactation, or those without taking effective contraceptive measures.
2. Subjects with syphilis or HIV positive antibody.
3. Subjects with infection aggravated within the past month.
4. Subjects suffering from any of the following pulmonary diseases: active tuberculosis, pulmonary embolism, pneumothorax, multiple huge bullae, uncontrolled asthma, severe pneumonia, acute exacerbation of chronic bronchitis, AECOPD, severe and / or extremely severe COPD, etc..
5. Subjects suffering from other serious diseases, such as myocardial infarction, unstable angina, cirrhosis, and acute glomerulonephritis.
6. Subjects with progression-free survival (PFS) less than 0.5 years or Karnofsky performance scores less than 60 points.
7. Subjects with leukopenia (WBC less than 4x109 / L) or agranulocytosis (WBC less than 1.5x109 / L or neutrophils less than 0.5x109 / L) caused by any reason.
8. Subjects with severe renal impairment, serum creatinine> 1.5 times the upper limit of normal.
9. Subjects with liver disease or liver damage: ALT, AST, total bilirubin> 2 times the upper limit of normal
10. Subjects with a history of mental illness or suicide risk, with a history of epilepsy or other central nervous system disorders.
11. Subjects with severe arrhythmias (such as ventricular tachycardia, frequent superventricular tachycardia, atrial fibrillation, and atrial flutter, etc.) or cardiac degree II or above conduction abnormalities displayed via 12-lead ECG.
12. Subjects with a history of alcohol or illicit drug abuse.
13. Subjects accepted by any other clinical trials within 3 months before the enrollment
14. Subjects with poor compliance, difficult to complete the study.
15. Any other conditions that might increase the risk of subjects or interfere with the clinical trial.