Positron Emission Tomography and Computed Tomography in Guiding Radiation Therapy for Stage III Non-small Cell Lung Cancer

Inclusion Criteria: * Patients must have FDG-avid (maximum SUV \>= 4.0) (from PET scan of any date, any scanner) and histologically or cytologically proven non-small cell lung cancer * Patients must be clinical American Joint Committee on Cancer (AJCC) stage IIIA or IIIB (AJCC, 7th ed.) with non-operable disease; non-operable disease will be determined by a multi-disciplinary treatment team, involving evaluation by at least 1 thoracic surgeon within 8 weeks prior to registration; Note: For patients who are clearly nonresectable, the case can be determined by the treating radiation oncologist and a medical oncologist, or pulmonologist * Patients with multiple, ipsilateral pulmonary nodules (T3 or T4) are eligible if a definitive course of daily fractionated radiation therapy (RT) is planned * History/physical examination, including documentation of weight, within 2 weeks prior to registration * FDG-PET/CT scan for staging and RT plan within 4 weeks prior to registration * CT scan or sim CT of chest and upper abdomen (IV contrast is recommended unless medically contraindicated) within 6 weeks prior to registration * CT scan of the brain (contrast is recommended unless medically contraindicated) or MRI of the brain within 6 weeks prior to registration * Pulmonary function tests, including diffusion capacity of carbon monoxide (DLCO), within 6 weeks prior to registration; patients must have forced expiratory volume in 1 second (FEV1) \>= 1.2 Liter or \>= 50% predicted without br…