The purpose of this study was to research on the safety and feasibility of ISR combined with low energy X ray intra-operative radiotherapy for the patients with local advanced rectal cancer.

Inter-sphincteric resection (ISR) has become an increasingly popular optional surgical tool for the treatment of very low rectal cancer. Nowadays, preoperative criteria for Lap ISR were the patients whose diagnosed with clinical stages T1-2 and N0_1, which only a few patients with early stages can benefit from it. However, intra-operative radiotherapy with low energy X ray applied by Intrabeam is becoming an accepted radiotherapy technique for treatment of cancers. The purpose of this study was to research on the safety and feasibility of ISR combined with low energy X ray intra-operative radiotherapy for the patients with local advanced rectal cancer.

Inclusion Criteria:

• those whom were preoperatively assessed to be in clinical stageT3 or has lymphatic metastasis by MRI or ultrasonic endoscopy;
• the lower edge of the tumor is away from the anal edge by less than 5 cm, or away from the dentate line by less than 3cm;
• in intra-operative separation, the lower edge of the tumor is below the plane of the levator ani muscle or the tumor is hard to separate;
• those in T4 stage and could be radically resected by intra-operative surgeon assessment;
• adequate preoperative sphincter function and continence; (vi)local spread restricted to the rectal wall or the IAS.
• absence of distant metastases.

Exclusion Criteria:

• clinical T4 tumors based on the Union for International Cancer Control UICC TNM classification (7th edition):
• infiltrating gross appearance of the tumors;
• poorly differentiated adenocarcinoma by biopsy specimens;
• a degree of preoperative incontinence.

When the investigators complete the study and publish our data.

Patients will be assigned to two different groups and receive intraoperative radiation randomly. The care provider and investigator also don't know the concrete situation of the patients.