Would you recommend repeat radiation therapy for a painful perineal recurrence in a patient who failed definitive CRT, and recurred again after salvage abdominoperineal resection (APR)?

I think repeat radiation therapy is certainly an option that can be offered to this patient, especially if the interval between treatments is long. MD Anderson reported on a series of 10 patients with anal SCCs treated with reirradiation after definitive CRT (https://www.ncbi.nlm.nih.gov/pubmed/27755060) with a median dose of 39 Gy in 1.5 Gy bid fractions. For pelvic reirradiation in the setting of recurrent rectal cancers, 30 Gy in 1.5 Gy bid fractions were typically used if the re-treatment interval was <1 year and 39 Gy used if the interval was >1 year and generally just the GTV with about a 1.5-2cm PTV margin was treated. With this fractionation, toxicity seems to be acceptable. In that series specific to anal cancer patients, they repo...

I would add that if the recurrence is not exceedingly thick then concurrent hyperthermia with re-irradiation is a feasible option, especially in a patient who cannot tolerate concurrent chemotherapy. I have personally used External thermal therapy (ETT) is this setting and patients have had excellent outcomes and tolerance. Our institution's experience has demonstrated the same: http://www.redjournal.org/article/S0360-3016(15)02789-3/abstract