Is there a role for checking calprotectin, or other markers of inflammation, in decision making or monitoring in patients undergoing abdominopelvic radiotherapy with history of IBD?  

The fecal calprotectin is neither sensitive nor specific enough to determine the protocol for radiotherapy. In fact, the very disease requiring the radiation may contribute to the results! If you need to know the condition of the rectosigmoid, a flexible sigmoidoscopy should be your best bet.