Online adaptive radiotherapy has demonstrated to be feasible to reduce inter-fractional radiotherapy errors as it re-optimizes treatment plan every fraction. To investigate the extent and value of margin reduction，we conduct a prospective clinical trial to determine the optimal margin and toxicity of smaller margin.

This is a prospective phase II clinical trial with an anticipated total of more than 380 radiotherapy fractions of 15 patients to evaluate optimal margin of iterative cone-beam computed tomography（iCBCT） guided online adaptive radiotherapy （oART） for postoperative treatment of endometrial and cervical cancer. Postoperative endometrial and cervical cancer patients with following characteristics are included in the present study:（a）underwent radical surgery （b）no residual tumor at the resection margin by postoperative pathology（c）pathological findings indicate risk factors but no metastasis (d) adjuvant radiotherapy are prescribe (e)without evidence of para-aortic metastatic lymph nodes. Five patients （almost 125 fractions）treated with oART have the target volume contoured on pre-treatment iCBCTs and end-treatment iCBCTs. Anterior-posterior, lateral, and superior-inferior shifts were calculated and the average shift in all directions was calculated. A clinical target volume (CTV) to planing tumor volume (PTV) expansion is determined and verifies on a validation cohort of 10 patients (almost 250 fractions) treated with oART. Record acute toxicity from the start of treatment to 3 months after treatment.

Inclusion Criteria:

1. Patients must be informed of the investigational nature of this study and give written informed consent before treatment.
2. Postoperative endometrial and cervical cancer patients with pathologically confirmed no residual tumor at the resection margin and no evidence of distant metastasis (FIGO stage IVB).
3. Pathological findings indicate risk factors and adjuvant radiotherapy are prescribe.
4. Karnofsky score ≥ 70.
5. Subjects aged ≥ 18 years and ≤ 70 years.
6. No evidence of para-aortic metastatic lymph nodes.
7. No contraindications to CT scanning.
8. Subjects must be able to cooperate in completing the entire study.
9. Adequate marrow: neutrophile granulocyte count ≥1.5*10^9/L, hemoglobin ≥ 80 g/L, platelet count ≥100*10^9/L.
10. Normal liver and kidney function: Creatinine (Cr) < 1.5 mg/dl, Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST) < 2*upper limit of normal (ULN).

Exclusion Criteria:

1. Subjects who have received prior pelvic radiotherapy.
2. Subjects with other primary malignancies.
3. Subjects with contraindications to radiotherapy, as determined by the investigators.
4. Any severe disease which may bring unacceptable risk or affect the compliance of the trial, for example, unstable cardiac disease requiring treatment, renal disease, chronic hepatitis, diabetes with poor control, and emotional disturbance.
5. Active infection with fever.
6. Active inflammatory bowel disease.