Radiation is treatment with high-energy rays (such as x-rays) to kill or shrink cancer cells. After surgery, radiation can kill small deposits of cancer cells that may not be seen during surgery.

After transurethral surgery, a combination of radiation therapy and chemotherapy is sometimes able to completely destroy cancers that would otherwise require cystectomy. If the tumor is in a position that makes surgery difficult, radiation may be used to shrink the tumor, making surgery easier. Radiation might also be used to ease the symptoms of advanced cancer or limit bleeding from inoperable tumors.