Oral mucositis (inflammation of the lining of the mouth) is a very common adverse effect when chemotherapy and radiation therapy are used to treat cancer. Mucositis occurs in about 40% of patients receiving standard dose chemotherapy, 80% of patients receiving radiation therapy of the head and neck, and up to 100% of patients undergoing a bone marrow transplant. Because the pain from mucositis can be so bad it can cause the inability to eat or drink, inability to talk, gagging and drooling. Many times mucositis can affect cancer treatment because patients may have to be given a lower dose of a drug or stop treatment completely. There are not many treatments today that can help relieve the severe pain caused from mucositis. This research study will help researchers determine if using an oral mouthwash called Ketamine will help lessen mucositis pain.