Pulmonary effects of radiation therapy.

The cellular effects of irradiating the lungs are rleated to the histologic and clinical sequelae. The occurrence and severity of damage rare semiquantitatively related to the volume of lung irradiated, and the dose rate of irradiation. The clinical syndrome occurs in up to about 10% of patients and consists of an acute transient phase, radiation pneumonitis, usually occurring 6 to 12 weeks after radiation therapy. This is followed by clinical remission except in the most severe cases and gradula radiologic progression to the stage of radiation fibrosis over the next 6 to 12 months. Concommittant chemotherapy, repeat courses of radiation, and steroid wihtdrawal are exacerbating factors. Characteristic changes in pulmonary function and radiographic appearance are described, and management is reviewed.