Chronic Radiation Injury
Chronic radiation proctitis is a common entity occurring in up to 75% of patients receiving pelvic radiation therapy. Symptoms are similar to those experienced in an acute injury with the exception of bleeding being more of a problem. It is important, when these symptoms occur, to mention prior radiation exposure to the physician as symptoms may first occur many years later. The doctor will want to perform an examination and tests to make a diagnosis. A flexible sigmoidoscopy (examination of the inside of the sigmoid colon and rectum using a thin, lighted tube called an endoscope) will be sufficient in identifying the injured colon. However, in those persons having a family history of colon cancer, age greater than 50, or possible inflammatory bowel disease, it would be appropriate for the doctor to perform a full evaluation by colonoscopy (endoscopic exam to inspect the entire colon and rectum).
A doctor may find very subtle changes using an endoscopic approach, such as loss of normal folds in the colorectal lining (mucosa) or mild redness. More advanced or obvious findings may include ulcerations, easily damaged blood vessels, and/or abnormal narrowings (strictures). These visible endoscopic changes occur as a result of chronic inflammation, formation of scar-like tissue (fibrosis), and injury from low blood flow (ischemia). During the colonoscopy, the doctor may also decide to cautiously remove tissue for microscopic examination (biopsy). Once the diagnosis has been confirmed, it becomes important to discuss the available treatment options with the physician.
Other medical conditions such as diabetes and atherosclerosis (clogging and narrowing of arteries) affect the circulatory system and can increase the risk of chronic radiation injury. It is important to let the doctor know if these conditions are present.
Treatment – The 5-ASA agents used to treat acute radiation injury tend to be less effective when used in treating chronic changes. This is likely a result of the underlying changes due to scar tissue and ischemic injury. Sucralfate enemas have been shown to decrease the risk of bleeding and are generally well tolerated.
When bleeding is resistant to first line therapies, a doctor may try using a topical formaldehyde application to decrease bleeding. While relatively easy to apply in an office setting, it has been associated with adverse events (fistula formation and bowel perforation). Another method, argon plasma coagulation (APC), does not require contact with the tissue. During a colonoscopy, a probe is aimed at the injured blood vessel and a jet of electrically charged gas is emitted that coagulates the lesion and helps prevent further bleeding. Depending on the extent of bleeding, 3–4 applications may be required to achieve complete resolution. 5-ASA suppositories or steroid enemas can be used to speed-up healing of any ulcers that may form with the use of APC.
Surgery is only occasionally needed. It is reserved for severe cases that do not respond to other treatments because problems may arise due to poor healing where the colon is surgically rejoined. It is thought that the injured blood vessel supply network contributes to the poor healing.