Radiation-Induced Lung Disease

Radiologic manifestations are usually confined to the lung tissue within the radiation port and are dependent on the interval after completion of treatment. The radiological changes are expected 8 weeks after 4000 rad, and 1 week earlier for each 1000 rad increments above 4000. In the acute phase (2 to 6 weeks), radiation injury typically manifests as ground-glass opacity or as consolidation; in the late phase, it typically manifests as traction bronchiectasis, volume loss, and scarring. However, the use of oblique beam angles and newer irradiation techniques such as three-dimensional conformal radiation therapy or hypofractionated stereotactic radiotherapy can result in an unusual distribution of these findings. Awareness of the typical and atypical manifestations of radiation-induced lung disease can be useful in differentiating from infection, recurrent malignancy, lymphangitic carcinomatosis, and radiation-induced tumors. Findings such as the late appearance or enlargement of a pleural effusion, development of consolidation, opacification of a previously demonstrated air bronchogram, a mass, or cavitation suggest recurrence of malignancy and/or infection. Because radiation pneumonitis can have increased fluorodeoxyglucose (FDG) uptake that mimics recurrent disease, fluorodeoxyglucose positron emission tomography (FDG PET) is best performed at least 3 months after completion of radiation therapy or before lung radiation-induced lung injury. FDG PET has, however, high negative predictive value, and focal opacities with low FDG uptake can be followed radiographically.

Approximately 10% of patients receiving lung radiation will develop clinical disease usually 2 to 6 months after the initiation of therapy. Radiographic changes following radiation therapy can be seen in up to 42% of patients. Drug toxicity can be synergistic and may occur even if the drugs and radiotherapy are separated in time, as many as 10% of patients receiving chemotherapeutic agents will develop an adverse drug reaction in their lungs. The most common drugs resulting in lung toxicity are bleomycin, methotrexate, carmustine, busulfan, and cyclophosphamide.

Drug-Induced Lung Disease