RATIONALE: Specialized radiation therapy that delivers a high dose of radiation directly to the tumor may kill more tumor cells and cause less damage to normal tissue. Drugs, such as pemetrexed and erlotinib, may make tumor cells more sensitive to radiation therapy. Erlotinib and pemetrexed may also stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Giving intensity-modulated radiation therapy together with pemetrexed and erlotinib may kill more tumor cells.