CT demonstration of pulmonary effects of tangential beam radiation.

Breast cancer is sometimes treated with an excisional biopsy and a radiation portal limited to the breast and the adjacent chest wall, especially in patients with negative lymph node dissections. The beam passes through this portion of the chest wall tangentially. Such radiation can result in changes in the included lung parenchyma that are pleural-based and sharply demarcated from the normal lung on CT lung windows. In our experience CT lung windows were more sensitive than chest radiography in showing these changes. Such changes must be recognized and differentiated from pleural metastases. Computed tomography also resulted in a more specific diagnosis than chest radiography because it better localized the abnormality to the radiation portal.