1. irradiation dose, time

Pelvic area radiotherapy 4 ~ 4.5 weeks of irradiation less than 4200 ~ 4500rad, the incidence of a gradual increase; such as increasing the dose of irradiation, the incidence of rapid increase. It is generally estimated that the incidence rate is about 8℅ when the irradiation dose exceeds 5000rad in 5 weeks.

2. Different parts of the intestine have different sensitivities to irradiation

The tolerance is: rectum> small intestine, colon> stomach.

3. Different mobility of different parts of the intestine

Because the terminal ileum and distal colon are more fixed, they are more susceptible to damage by irradiation. Inflammation or postoperative adhesions make the bowel semi-fixed, limiting the activity of the bowel segment, increasing the irradiation per unit area of that segment and increasing the morbidity.

4. Hysterectomy

After total hysterectomy, the irradiation of the rectum is higher than that of those who have not had it removed.

5. Other underlying conditions

Arteriosclerosis, diabetes, and hypertension patients with pre-existing vascular disease, irradiation is more likely to cause damage to the gastrointestinal tract.