In patients with active IBD and rectal cancer, do you take any precautions before starting TNT?

First, I would be sure that the patient really needs TNT. If a patient has active inflammatory bowel disease, they will not tolerate TNT very well. If a patient has inactive IBD, there is not likely to be much added morbidity. I would be very hesitant to use TNT if someone has really active IBD. There are other alternatives. One is to do a diversion first- that will help, but there still could be problems with high output through a stoma. The second is to start with resection. Although not ideal, it still may be the better option. Also, one needs to consider whether the IBD is located just in the colon or in the small intestine. That should impact on the radiation fields that are used. Both fluoropyrimidines and radiation produce mucosal loss and will exacerbate IBD symptoms. Another possibility is to use short course RT and immediate surgery so there is little time for the RT reaction (if the IBD is colonic). Chemo would then come postop.

I agree with @Dr. First Last's comments and would add that the value of the current widespread trend of the use of TNT is in the realm of non-operative management. If that is not the plan, giving all the treatment upfront is often over-treatment. I would make sure there is an indication for radiation after consideration of the results of the PROSPECT trial. Likewise, there is abundant evidence that if there is a pCR after chemoradiation, the relapse free survival after surgery is very low (<10%) without the use of adjuvant chemotherapy. For this reason, many of our colleagues in Europe do not give adjuvant chemotherapy to these patients, and exposing these patients to the risk of peripheral neuropathy from oxaliplatin is unreasonable considering 5-FU or capecitabine would be better tolerated and may help reduce the risk as much with lower toxicity risk. If there is active inflammatory bowel disease and neoadjuvant radiation is considered the best option, I would consider reducing the dose to 45 Gy in 25 Fx if the acute reactions are severe towards the end of treatment.