Hey Rob and Adriana,
I'm not certain, but I would mostly likely attribute the diarrhea to the "lumbar" radiation. There is a lot of gut that can be incidentally affected in that process. Years ago my father-in-law suffered with many problems post radiation (for colon cancer) in that area…diarrhea being one of those. Oddly enough, when dealing with diarrhea due radiation patients need to INCREASE fiber – in forms like psylium, guar gum, inulin, or other soluble fiber product – as soon as possible. Advice is to begin with one dose per day, per package instructions, increasing to three doses daily as tolerated. Often this is started with radiation treatment. Patients are advised to snack on dry salty foods – like saltine crackers or dry toast. Avoid hard to digest foods like popcorn, peas, corn, raw veg, cruciferous veg, spicy foods, sugar free foods (sorbital). Avoid greasy foods. Eat yogurt with live active cultures…or kefir or buttermilk 4-8 ounces per day. Use other dairy products only if taking lactase tabs. Eat foods with soluble fiber – like oatmeal, bananas, apple sauce, peaches and pears. No beans. Avoid insoluble fiber like fresh fruits/veg and whole grain bread. Some advise to try rice congee….Combine one cup white rice (uncooked) with 6-7 cups of water and 1 teaspoon of salt. Bring to a boil, then simmer until you have a sticky soupy mixture…usually about 40 minutes. Sip and eat mixture. Broth may be used instead of water if you prefer.
It may seem daring (or unwise) to add fiber when already having diarrhea…but oddly enough…adding bulk may add subtance and therefore, decrease the liquidity of the stools. However, you two will have to do what you think best…but I thought I'd let you know this bit….for what it may be worth.
Probiotics are over the counter in pill form these days. They wouldn't hurt and may be helpful.
One final possibilty may be the use of sandostatin. This is a prescription medication you could ask your doc about. It is an injection that is given sub q….kind of like insulin shots.
I would start with the diet change and the probiotics. If that didn't help…I would try the sandostatin.
Diarrhea is a common problem after radiation to the gut. You can google it for much more info. It can last weeks to months. And I can't be sure this is what you are dealing with….but these would be the things I'd try at this point.
You are two of my most amazing and precious peeps. Holding you in my heart and sending much love and hugs. celeste
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, and 2x we live in the Seattle area. 
Working through the 24/7. I am setting up being to become a paid (albeit low $) caregiver via benefits available from Medicaid which should provide a little relief as I am unable to take on most photography jobs now. Looking to train her sister to provide some back-up help too. 
