The large and small bowel are very sensitive to radiation. The amount of damage to normal tissues increases as the radiation dose increases and, since larger doses are needed for most tumors in the abdomen and pelvis, enteritis is likely to occur. Almost all patients undergoing radiation to the abdomen, pelvis, or rectum will show signs of acute enteritis. Acute symptoms are those that appear during the first course of radiation therapy and up to 8 weeks later. Chronic radiation enteritis may appear months to years after finishing radiation therapy or it may begin as acute enteritis and continue after treatment stops.
Several factors determine the occurrence and severity of radiation enteritis.
The risk of radiation enteritis usually increases as the dose of radiation and the percentage of normal bowel treated increases. Also, the patient factors listed above can decrease blood flow to the bowel wall and affect bowel movement, increasing the chance of radiation injury. An increasing number of cells die, and this leads to other problems over the next few days and weeks. Patients with acute enteritis may complain of nausea, vomiting, abdominal cramping, the frequent urge to have a bowel movement, and watery diarrhea. With diarrhea, the gastrointestinal tract does not function as efficiently, and fat, lactose, bile salts, and vitamin B12 are not well absorbed.