Can radiation therapy to the prostate cause diarrhea?

Radiation Therapy to the Prostate Commonly Causes Diarrhea

Yes, radiation therapy to the prostate commonly causes diarrhea, affecting approximately 25% to 50% of men after treatment. 1 This gastrointestinal side effect is a well-documented complication of pelvic radiation that can significantly impact quality of life.

Incidence and Duration

• Diarrhea and loose stools are common after external beam radiation therapy (EBRT), typically affecting 25-50% of men following treatment 1
• These symptoms can persist for two to three years after radiotherapy in some patients 1
• Generally, about 60% of patients experience temporary mild diarrhea during pelvic radiation treatment 1
• The Prostate Cancer Outcomes Study demonstrated that bowel side effects were more common among men who received radiotherapy compared to those who underwent radical prostatectomy 1

Pathophysiology of Radiation-Induced Diarrhea

Radiation causes diarrhea through several mechanisms:

• Direct damage from energy absorption and free radical release from radiation interacting with cellular water 1
• Injury to stem cells within intestinal crypts, leading to reduced mucosal integrity and flattening of intestinal villi 1
• Modification of intestinal microflora and deterioration of enzymatic activities 1
• Decreased absorptive intestinal surface area and reduced intestinal transit time 1
• Possible lactose malabsorption that develops as a side effect of pelvic radiation 1
• Cholerheic enteropathy from ileal dysfunction, with impaired bile salt absorption 1

Risk Factors

Several factors influence the risk of developing radiation-induced diarrhea:

Patient-Related Factors:

• Low BMI 1
• Comorbid diseases (diabetes, hypertension, collagen vascular diseases, inflammatory bowel disease) 1
• Smoking history 1
• Previous intestinal or abdominal surgery 1, 2

Treatment-Related Factors:

• Volume of small bowel in radiation field 1
• Radiation dose (acute side effects to intestine occur at 10 Gy; curative doses for pelvic tumors range between 50-75 Gy) 1
• Fractionation schedule (hypofractionation may increase risk beyond standard linear-quadratic model correction) 2
• Radiation technique (IMRT vs. 3D-CRT) 1
• Concomitant chemotherapy administration 1

Timing and Classification

• Acute diarrhea: Occurs during radiation therapy or within 3 months of treatment 1
• Chronic diarrhea: Lasts for or develops after a longer period 1
• Some studies indicate that bowel problems can linger for two to three years after radiotherapy 1

Associated Symptoms

Radiation-induced diarrhea may be accompanied by:

• Nausea and vomiting 1
• Abdominal cramping 1
• Rectal tenesmus 1
• Bowel urgency and increased stool frequency 1
• Rectal pain (affecting 12-39% of men in the year after EBRT) 1

Treatment Options

For management of radiation-induced diarrhea:

• Probiotics containing Lactobacillus species are suggested to prevent diarrhea in patients receiving radiation therapy for pelvic malignancies 1
• Systemic sulfasalazine (500 mg orally twice daily) is suggested to prevent radiation-induced enteropathy in patients receiving pelvic radiation 1
• Loperamide for symptomatic management 1
• Dietary counseling to address potential nutrient malabsorption 1
• Intravenous amifostine (≥340 mg/m²) is recommended to prevent radiation proctitis 1

Important Considerations

• Combining interstitial prostate brachytherapy with EBRT can result in higher rates of complications (including diarrhea) than treatment with brachytherapy alone 1
• Not all post-radiation bowel symptoms are due to radiation effects; other diagnoses including malignancy should be considered 3
• In one study, only 4% of patients with post-radiation bowel symptoms had radiation proctopathy without associated pathology 3
• Modern radiation techniques like IMRT may reduce but not eliminate the risk of gastrointestinal toxicity 4

Long-term Impact

• Even after 5 years, patients treated with radiation therapy continue to experience significantly higher rates of new GI toxicities than those managed conservatively 4
• The cumulative incidence of patient-reported severe bowel problems at 5 years was 8% in dose-escalated radiation therapy 5
• Prevalence of moderate and severe toxicities generally increases up to 3 years and then lessens 5

Patients undergoing radiation therapy for prostate cancer should be informed about the risk of diarrhea and other gastrointestinal side effects, and appropriate preventive and management strategies should be implemented to minimize impact on quality of life.