Radiation Enteritis of the Large Bowel

Anatomical Distribution of Radiation Enteritis

• The rectum is the most commonly affected segment of the large bowel in radiation enteritis due to its fixed anatomical position in the pelvis and proximity to organs commonly treated with radiation therapy 1, 2
• Radiation-induced proctitis is a common complication of pelvic radiation therapy, occurring due to the rectal proximity to pelvic organs and its fixed position 1

Pathophysiology of Radiation Enteritis

• Radiation damage occurs through direct energy absorption and free radical release from radiation interacting with cellular water 3, 2
• Damage to stem cells within intestinal crypts leads to reduced mucosal integrity and flattening of intestinal villi 3
• Radiation induces arteriole endarteritis, submucosal connective tissue fibrosis, and neoangiogenesis followed by telangiectasias in the rectal wall 1
• Modification of intestinal microflora and deterioration of enzymatic activities contribute to radiation enteritis 3
• The fixed position of the rectum makes it particularly vulnerable to cumulative radiation exposure compared to more mobile segments of the bowel 1, 2

Clinical Presentation

• Bleeding is the most common symptom of radiation proctitis 1
• Loss of distensibility due to rectal wall fibrosis results in tenesmus and defecation difficulties 1
• Acute radiation proctitis occurs almost immediately after starting radiation therapy and lasts up to 3 months 1
• Chronic radiation proctitis may begin during the acute phase but symptoms typically become apparent 8-12 months after completing radiation therapy 1

Risk Factors for Radiation Enteritis

• Large irradiated volume, radiation dose (>45 Gy or above 70 Gy), and older radiation techniques (3D-CRT vs. IMRT) increase risk 1
• Patient-related risk factors include low BMI, diabetes mellitus, vascular disease, arterial hypertension, atherosclerosis, inflammatory bowel disease, collagen disease, and HIV infection 1, 2
• Previous intestinal surgery may predispose to radiation enteritis due to anatomical changes leading to increased bowel exposure to radiation field 3
• Concomitant chemotherapy, particularly with fluoropyrimidines, increases the risk and severity of radiation enteritis 3

Prevention and Management

• Intensity-modulated radiation therapy (IMRT) is associated with significantly less rectal toxicity than 3D conformal radiation therapy (3D-CRT) 1
• Image-guided radiation therapy (IGRT) reduces the risks of target miss and/or organs at risk overdose during radiation therapy delivery 1
• Probiotics during treatment can significantly reduce acute toxicity 4
• Treatment of acute radiation enteritis includes probiotics to restore intestinal microbiota, loperamide for symptom control, and dietary counseling 1, 2

Clinical Implications

• About 90% of patients who receive pelvic radiation therapy may develop permanent changes in bowel habits 3
• Quality of life is affected by gastrointestinal symptoms in 50% of patients (moderate to severe effect in 20-40% of cases) 3
• Regular follow-up evaluation is essential to assess late toxicity for early intervention by a specialist multidisciplinary team 1

Management of Post-Radiation Colitis

Pathophysiology and Clinical Presentation

• Post-radiation colitis is an ischemic problem caused by arteriole endarteritis, submucosal fibrosis, and neoangiogenesis leading to telangiectasias, resulting in symptoms such as bleeding, tenesmus, and defecation difficulties in patients who have undergone pelvic radiotherapy 5, 6
• Bleeding is the most common symptom, occurring in up to 50% of patients after pelvic radiotherapy, typically appearing months after treatment and peaking within 3 years 5, 7

Appropriate Management

• The American Gastroenterological Association recommends optimizing bowel function and stool consistency, and stopping or reducing anticoagulants/antiplatelet agents if medically safe, as first-line management for post-radiation colitis 5, 8, 7
• Sucralfate enemas are the primary medical intervention for post-radiation colitis, administered via soft Foley catheter inserted rectally, with the patient rolling through 360 degrees to coat the entire rectal surface 8, 9
• Ablative therapies such as argon plasma coagulation, heater probe, and formalin therapy may be considered for patients who fail medical management, but carry significant risk of serious complications in radiation-damaged tissue 8, 9

Important Considerations

• Patients with post-radiation colitis should undergo flexible sigmoidoscopy or colonoscopy to confirm radiation-induced telangiectasia and exclude alternative pathology, with biopsy avoided unless neoplastic process is strongly suspected 5, 8, 7
• Informed consent is necessary before proceeding with ablative treatments, due to the significant risk of serious complications in radiation-damaged tissue 5, 8, 7

Management of Severe Radiation Proctitis

Immediate Stabilization Goals

• Assess and correct volume status through IV fluid resuscitation if active bleeding is present, as severe complications including hemorrhage occur in 10% of cases 10, 11
• The primary goals are to control bleeding, manage pain, prevent complications, and restore bowel function to preserve quality of life, with admission orders focused on hemodynamic stabilization, bowel rest, and initiation of topical anti-inflammatory therapy 10, 11

Medical Management Goals

• Initiate topical anti-inflammatory products such as sulfasalazine or mesalamine alone or combined with steroids for Grade 1/2 proctitis, as these are the recommended first-line treatments 10, 11
• Administer sucralfate enemas via soft Foley catheter inserted rectally, with the patient rolling through 360 degrees to coat the entire rectal surface 12
• Consider loperamide for diarrhea control if present 11
• Maintain adequate hydration as part of basic bowel care 12

Diagnostic and Monitoring Goals

• Perform sigmoidoscopy to investigate patient-reported bleeding or evidence of occult fecal blood to confirm radiation-induced telangiectasia and exclude alternative pathology 10, 11
• Evaluate for severe complications including hemorrhage, necrosis, and perforation that occur in 10% of cases 10, 11
• Assess for signs of chronic proctitis, which results from vascular endothelial cell damage developing with latency of 1-25 years 10

Advanced Treatment Planning

• Consider hyperbaric oxygen therapy if initial treatments fail, as it induces neo-vascularization, tissue re-oxygenation, collagen neo-deposition, and fibroblast proliferation, eliciting responses in the majority of patients with chronic proctitis 10, 11
• Plan for Argon Plasma Coagulation if medical management fails, as repeated applications resolve 80-90% of chronic proctitis cases with bleeding 10, 11
• Obtain early surgical consultation for refractory cases, as surgery may be required but carries high morbidity up to 60% 10

Quality of Life Preservation

• Note that in 20% of cases, anal or rectal pain resolves spontaneously 10, 11

Critical Pitfalls to Avoid

• Do not use oral sucralfate, as it does not prevent acute diarrhea and is associated with more gastrointestinal side-effects including rectal bleeding compared to placebo 12
• Avoid cytoprotective agents like sucralfate, balsalazide, mesalazine, and misoprostol for prevention, as they should not be treatment of choice due to conflicting evidence on efficacy 10, 11