Patients with lung cancer may develop a second primary tumor or recurrent disease after previous radiotherapy. Surgical salvage therapy is the mainstay of therapeutic options. However, in case of irresectable disease, re-irradiation should be considered. Also in the postoperative setting, re-irradiation is considered after surgical salvage in case of features in the pathology specimen indicating a high risk for subsequent recurrence. However after re-irradiation, there is a high risk of 43% grade 3 (late) toxicity at 5 years (including possible fatal complications) and a relatively low chance of locoregional control of 50% at 5 years. One out of three patients survives re-irradiation without recurrence and severe complications. Improvements in both the risk of radiation-induced complications and the oncological outcome are thus warranted.