Chronic Radiation Induced Bowel Toxicity Study

This study is looking at how radiation treatment for prostate cancer affects the bowel over time, and whether factors like gut bacteria play a role in the severity of bowel side effects. **You may be eligible if...** - You are male and at least 18 years old - You have been newly diagnosed with intermediate to high-risk prostate cancer confined to the prostate - You are scheduled to receive a specific type of radiation treatment (IMRT, 60 Gy in 20 treatments) - Your general health is reasonably good **You may NOT be eligible if...** - You have taken antibiotics in the past 2 months - You have had chemotherapy or immunosuppressive therapy in the past 6 months - You have taken high-dose commercial probiotics in the past 12 months - You have inflammatory bowel disease, celiac disease, or a history of colorectal cancer - You have had part or all of your colon removed - You have a history of diverticulitis (inflamed pouches in the colon) Talk to your doctor to see if this trial is right for you.