How would you manage a patient with T3N0 rectal cancer status post transanal excision, who is not a surgical candidate, and who received pelvic radiation for prostate cancer 20 years ago?

Abdominal or abdominoperineal resection. T3 tumors have a 20+% risk of recurrence despite radiation and local excision. If truly T3N0, the risk may be the same with surgery. And reirradiation is fraught with risk.