Fluciclovine F18

This phase II trial tests effects of nivolumab in combination with chemotherapy drugs prior to radiation therapy patients with nasopharyngeal carcinoma (NPC). Immunotherapy with monoclonal antibodies, such as nivolumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Chemotherapy drugs, such as gemcitabine and cisplatin, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Radiation therapy uses high energy x-rays, particles, or radioactive seeds to kill cancer cells and shrink tumors. Researchers want to find out what effects, good and/or bad, adding nivolumab to chemotherapy has on patients with newly diagnosed NPC. In addition, they want to find out if children with NPC may be treated with less radiation therapy and whether this decreases the side effects of therapy.