Radiation therapy of the chest has become part of standard regimens to treat limited-stage small-cell and locally advanced (stage III) non-small-cell lung cancer (NSCLC), and it is also used in other types of malignancies such as breast cancer and lymphoma. Recent advances in radiation techniques were aimed at minimizing radiation exposure to normal tissue. With the use of three-dimensional conformal radiation, it has been possible to target chest tumours much more precisely and to considerably exceed the traditional cut-off dose of 60 Gy (1 Gy equals 100 rad). These advances have resulted in improved local tumour control and prolonged survival in patients with locally advanced NSCLC. However, even with the most advanced planning techniques, normal tissue structures will inevitably be exposed to radiation, which may result in morbidity and even mortality. Radiation toxicity may develop acutely within a short time span after radiation exposure or occur as late as several years after therapy has been completed.