A 70-year-old man undergoes follow-up evaluation to determine treatment options following a third occurrence of bladder cancer. High-grade transitional cell carcinoma of the bladder was initially diagnosed 7 months ago following cystoscopy to evaluate painless hematuria. Transurethral resection of the bladder tumor (TURBT) was performed followed by administration of intravesical bacillus Calmette-Guérin (BCG). Three months later, surveillance cystoscopy identified recurrent superficial high-grade transitional cell carcinoma in the same location that was again treated with TURBT and BCG. Now, 4 months following the second episode, high-grade transitional cell carcinoma is again diagnosed. This time, the cancer is in the same location with an additional focus near the trigone. No evidence of invasion into the muscle layer of the bladder has ever been identified.

Physical examination findings, including vital signs, are normal.

CT scans of the abdomen and pelvis (done at the time of the second recurrence) identified no evidence of significant bladder wall thickening, regional lymphadenopathy, or evidence of metastatic disease.

Which of the following is the most appropriate treatment at this time?