Positive micro vascular invasion in early stage hepatocellular carcinoma(HCC) leads to early recurrence after surgery. Adjuvant external radiotherapy will be applied in those patients to see if disease free survival and overall survival could be approved.

Hepatocellular carcinoma(HCC) ranks the 6th most common cancer and is the 2nd leading cause of cancer-related death globally. Surgical resection remains the most efficient therapy in early stage. Though an anatomical resection of tumor lead to an up to 70% 5-year overall survival, the existence of micro vascular invasion(MVI) caused early recurrence. Stereotactic body radiation therapy (SBRT) has been proved to be efficient in treating vascular tumor thrombosis. The investigators tried to implement this technique in adjuvant setting for HCC after surgery with MVI. Participants with early stage HCC whose tumor locates closely to the main intrahepatic vascular will be regarded as potentially-not-enough-surgical-margin candidates. Surgical resection will be carried out as scheduled and an additional silver clip will be put into the margin. Postoperative pathological examination will detect micro vascular invasion or daughter nodule. MVI-positive candidates will be eligible for enrollment. Eligible participants will be randomized to two groups, SBRT group and surgery-alone(SA) group with 1-to-1 ratio. Participants in SBRT group will receive a 35Gy limited resection margin parenchyma SBRT after surgery, while participants in SA group just get surgery. Radiation related adverse events (AE) or reaction will be recorded and intervened necessarily. All participants will be followed up by investigators every three months. DFS, OS, and AEs are end points in this study.

Inclusion Criteria:

1. solitary nodule;
2. tumor adjacent to the main trunk of hepatic vein, cava vena, or to the major branch of portal vein (including the lobar branch at least);
3. macro-vascular negative;
4. no previous treatment before surgery;
5. no previous hepatic surgery;
6. Child-Pugh score A for hepatic function.

Exclusion Criteria:

1. spontaneous rupture;
2. pathologically proved positive resection margin;
3. severe cirrhosis with hypersplenism or esophageal and gastric varices;
4. 4-weeks postoperative examination revealed α-fetal protein(AFP) still positive or new lesion in remnant liver;
5. postoperative complications required a secondary operation or more than 3 weeks'recovery from surgery.

3 months from radiotherapy.

The adverse events were reported according to the CTCAE 5.0 version.