The risk of lung injury is a significant limiting factor in the use of thoracic radiotherapy for lung cancer. Given the high mortality and local failure rates in patients with unresectable lung cancer, a goal has been to increase the dose to the tumor as much as possible while trying to limit the damage to normal tissue. Efforts have been made to predict the risks for lung injury pretreatment, based on the planned dose and volume of lung treated, with mixed results. Complicating factors include performance status, underlying medical conditions, possible genetic predisposition to injury, and tumor location-associated changes in lung function. Much as a thoracic surgeon stratifies a patient's risk for pulmonary morbidity before resection, radiation oncologists should perform an assessment of patient specific factors that will impact on the potential toxicity of a given course of treatment. We present a proposed approach to the evaluation, risk assessment, and follow-up of patients treated with thoracic radiotherapy for lung cancer.