To study the application of Intersphincteric Resection（ISR）combined with intraoperative radiation therapy(IORT) for ultra-low rectal cancer,and to broaden the surgical indications of Intersphincteric Resection（ISR.

The study is aimed to assess the postoperative acute complication and the short-term acute efficacy on the patients with middle and low rectal cancer by treated with intraoperative radiotherapy,especially those with peritoneal inversion rectal cancer.

Abstract objective: To study the application of Intersphincteric Resection（ISR）combined with intraoperative radiation therapy(IORT) for ultra-low rectal cancer,and to broaden the surgical indications of Intersphincteric Resection（ISR）.

Methods: Patients, who were diagnosed with ultra-low rectal cancer and had strong desire of preserving anal function, will take part in the research,whose tumor invading the levator ani muscle or above, the diameter less than 6cm, the lower tumor margin away from the anal verge by less than 5cm and away from the dentate line by less than 3cm.They will undergo total mesorectal excision(TME) and ISR combined with IORT and prophylactic ileostomy.

Outcomes Measures:The evaluation of short term effects includes complications such as anastomotic leakage, acute radiation injury ,urinary dysfunction ,dysfunction of anal sphincter ,sexual dysfunction ,local recurrence , total life expectancy and expectancy without metastasis. The postoperative pathological examination reported to be moderately differentiated adenocarcinoma .We wili assess their postoperative acute complications and short-term efficacy .Their time of follow up visit wil be 1 year or more.

Inclusion Criteria:

Inclusion Criteria:

• Aged 40 to 80 years old, gender not limited.
• Be diagnosed as colorectal cancer by coloscopy.
• Patients with middle and low rectal cancer,whose preoperative staging evaluation is T3 ,T4 or N+.
• Accept surgery and intraoperative radiotherapy.
• Signed informed consent

Exclusion Criteria:

• the patients whose preoperative evaluation is below T3 stage with middle and rectal cancer.
• Active internal bleeding (such as gastrointestinal bleeding), urogenital system, or have not cure of peptic ulcer in four weeks
• Severe liver and kidney dysfunction
• Intracranial tumor, suspicious aortic dissection, arteriovenous malformation, aneurysm
• Thrombolysis treatment in one week
• Allergies of thrombolysis drug or contrast
• Participated in any clinical trials within three months

When the investigators complete the study and publish our data.

When the investigators complete the study and publish our data.