RATIONALE: Radiation therapy uses high energy x-rays to kill tumor cells. Erlotinib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Erlotinib may also make tumor cells more sensitive to radiation therapy. It is not yet known whether giving whole-brain radiation therapy together with erlotinib is more effective than whole-brain radiation therapy alone in treating patients with non-small cell lung cancer and brain metastases.