A 47-year-old woman presents with rectal pain and feculent discharge from her vagina. A digital rectal exam (DRE) in the office reveals a 4-cm, firm, palpable mass starting just below the dentate line; it is immobile and contiguous with the posterior vaginal wall. You perform a biopsy that confirms squamous cell carcinoma. After completing the staging workup, you find she has T4N0, stage IIIB disease. The recommended treatment is