Radiation Therapy and Stereotactic Radiosurgery With or Without Temozolomide or Erlotinib in Treating Patients With Brain Metastases Secondary to Non-Small Cell Lung Cancer

Inclusion Criteria: * Histologically confirmed non-small cell lung cancer * One to 3 intraparenchymal brain metastases by contrast-enhanced MRI, meeting the following criteria: * Well circumscribed tumor(s) * Maximum diameter ≤ 4.0 cm * If multiple lesions are present and one lesion is at the maximum diameter, the other lesions must not exceed 3.0 cm in maximum diameter * No metastases within 10 mm of the optic apparatus such that a portion of the optic nerve or chiasm would be included in the high-dose stereotactic radiosurgery boost field * No metastases in the brainstem, midbrain, pons, or medulla * No prior complete resection of all known brain metastases * Subtotal resection allowed provided residual disease is ≤ 4.0 cm in maximum diameter * No clinical or radiographic evidence of progression (other than study lesion\[s\]) within the past month * Patients with brain metastases at initial presentation do not require 1 month of scans documenting stable disease * Stable extracranial metastases allowed * No known or pre-existing liver metastases * No leptomeningeal metastases by MRI or cerebrospinal fluid evaluation * Synchronous brain metastases at initial diagnosis allowed * Performance status - Zubrod 0-1 * Hemoglobin ≥ 8 g/dL * Absolute neutrophil count ≥ 1,000/mm\^3 * Platelet count ≥ 100,000/mm\^3 * AST \< 2 times upper limit of normal (ULN) * Alkaline phosphatase \< 2 times ULN unless due to elevated bone metastases * Total bilirubin normal * Lactic dehydrogenase \< 2 times ULN * Creatinine \< 1.5 times ULN * No clinically active interstitial lung disease * Chronic stable asymptomatic radiographic changes allowed * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * HIV negative * Neurologic function status 0-2 * No other major medical illness or psychiatric impairment that would preclude study participation * No history of allergic reaction attributed to compounds of similar chemical or biologic composition to erlotinib or temozolomide * No concurrent immunotherapy * No concurrent biologic therapy, excluding growth factors and epoetin alfa * No prior temozolomide or erlotinib * No other concurrent chemotherapy during study radiotherapy * Other concurrent chemotherapy allowed after study radiotherapy, except for the following: * Temozolomide or erlotinib (arm I only) * Erlotinib (arm II only) * Temozolomide (arm III only) * No prior cranial radiotherapy * No concurrent intensity-modulated radiotherapy * Concurrent radiotherapy to painful bone lesions allowed * No concurrent radiotherapy to more than 15% of bone marrow * No other concurrent therapy for brain metastases unless a recurrence is detected * More than 30 days since prior investigational drugs * No concurrent enzyme-inducing antiepileptic drugs including, but not limited to, any of the following (for patients randomized to receive erlotinib): * Phenytoin * Carbamazepine * Rifampin * Phenobarbital * Primidone * Oxcarbazepine * No other concurrent investigational drugs * No concurrent Hypericum perforatum (St. John's wort) * No drugs that alter gastric pH (e.g., proton pump inhibitors or H2 antagonists) within 4 hours after erlotinib administration (arm III patients only)