This phase I trial studies the side effects and best dose of trametinib with or without whole brain radiation therapy in treating patients with brain metastases. Trametinib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Radiation therapy uses high energy x-rays to kill tumor cells and shrink tumors. Drugs, such as trametinib, may make tumor cells more sensitive to radiation therapy. Giving trametinib with whole brain radiation therapy may be a better treatment for brain metastases.