What is radiation colitis?
Radiation colitis refers to radiation-induced changes in the mucosa of the colon and rectum. Generally, radiation colitis is a chronic, ischemic process caused by obliterative endarteritis, in contrast to acute inflammation seen in other types of colitis.
Which part of the GI tract is most commonly injured by radiation?
Radiation injury to the colon occurs following treatment of rectal, cervical, uterine, prostate, urinary bladder, and testicular cancer. Because prostate cancer is the most common of these cancers, most data has been obtained in this group of patients. The peristaltic movement of the small intestine in and out of the field of radiation decreases the degree of injury to the small bowel. The colon, especially the rectosigmoid, is highly susceptible to radiation injury because it is immobile. Brachytherapy, or internal radiotherapy, can deliver high-energy radiation to more focused tissues and therefore causes less damage to the colon than external-beam radiation. Tumors in the pelvic area often require higher dosages of radiation and result in greater risk of damage to the colon.
What can be done to prevent radiation damage?
The extent of radiation colitis depends on the cumulative radiation dose, fraction size, technique of radiation delivery, amount of tissue exposed, and presence of other treatments such as surgery or chemotherapy. Of those listed, radiation dose appears to the most significant factor. Radiation damage can be reduced by limiting the dosage and area of exposure while shielding adjacent tissues. Additionally, amifostine has been shown to reduce the incidence of radiation colitis by scavenging free radicals produced during treatment.
What symptoms are associated with irradiation?
The initial symptoms of radiation exposure are nausea and vomiting. Diarrhea typically develops 5 days later. Loss of mucosal defenses increases the patient’s risk of developing sepsis. Acute radiation injury to the colon typically occurs within 6 weeks and is manifested by diarrhea, mucus discharge, tenesmus, and rarely, bleeding. These symptoms are self-limited and typically resolve in 2 to 6 months without therapy. Chronic symptoms of radiation colitis and proctitis (or chronic radiation proctopathy) can occur 9 to 12 months following radiation therapy, but can be delayed by decades after the initial radiation exposure. The primary symptoms associated with chronic injury to the colon and rectum include diarrhea, obstructed defecation, rectal pain, and rectal bleeding. Severe radiation colitis may manifest with bowel necrosis, perforation, fistula development, and uncontrolled rectal bleeding.
What are the effects of localized radiation to the colon?
Colonoscopy may be normal or may show telangiectasias, pallor, and friable mucosa. Early or acute changes include microscopic damage to mucosal and vascular epithelial cells, which may be asymptomatic to the patient. One common histologic feature is the presence of atypical fibroblasts. Late changes commonly involve fibrosis with obliterative endarteritis resulting in chronic ischemia, stricture formation, and bleeding.
How can radiation colitis and proctitis be managed?
There is limited data on the appropriate treatment for radiation colitis and proctitis. Medications used to treat radiation colitis and proctitis include oral and rectal sucralfate, steroids, 5-acetylsalicylic acid compounds, hyperbaric oxygen, and antibiotics, such as metronidazole. Stool softeners are also recommended, as straining can cause telangiectasias to bleed.
What are the endoscopic therapies for chronic bleeding?
The primary goal of endoscopic therapy is to treat telangiectasias, which are the most common source of rectal bleeding. Argon plasma coagulator, heater probe, and bipolar cautery have all been used. Colorectal surgeons may apply formaldehyde, also known as chemical cautery, to control bleeding. Patients should be transfused with blood as needed and take oral iron.
How are chronic, radiation-induced bowel strictures managed?
Patients with obstructive symptoms often benefit from the use of stool softeners. Balloon dilation of the strictures may be necessary. Patients with long or angulated strictures may benefit from surgery as these lesions are more likely to perforate with dilating procedures. Recurrent strictures may be treated with steroid injections. Colonic stents have also been used, but increase the risk of bowel perforation.