The purpose of this study is to determine whether ctDNA could help to evaluate whether to use drug adjuvant therapy after SBRT in patients with early lung cancer.

This is a prospective study. The purpose of this study is to determine whether MRD could help to evaluate whether to use drug adjuvant therapy after SBRT in patients with early lung cancer. The ctDNA was detected for early stage lung cancer patients before and after SBRT. If a high level of ctDNA was detected after SBRT, the patients were randomly divided into observation group and adjuvant treatment group.

Inclusion Criteria:

1. Patients pathologically diagnosed as non-small cell lung cancer, and was early stage（AJCC 8th）;

2. Patients aged between 18 -80 years; with expected survival time>3 months.

3. Patients with normal organ function within 30 days prior to treatment, the following criteria are met:

   1. blood routine examination criteria : i) hemoglobin (HB) ≥90g/L; ii) absolute neutrophil count (ANC) ≥1.5×10e9/L; iii) platelet (PLT) ≥80×10e9/L; b) biochemical tests meet the following criteria: i) total bilirubin (TBIL) ≤1.5 times of upper limit of normal (ULN); ii) alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤2.5 ULN; iii) serum creatinine (Cr) ≤1.5 ULN or creatinine clearance (CCr) ≥60mL/min;

Exclusion Criteria:

1. Patients with small cell lung cancer (including small cell carcinoma and non-small cell carcinoma mixed lung cancer);
2. Patients with factors that affect oral medication (such as cannot swallow, chronic diarrhea and intestinal obstruction, etc.) or intravenous medication;
3. Patients with any other severe and/or uncontrolled disease;
4. Patients with a history of psychotropic medicine abuse and cannot quit or have mental disorders;
5. Patients with disease which will severely endanger their security and could not complete this study, according to the judgement of researchers；