Radiation pneumonitis is a term describing the injury and inflammatory changes of the lungs as a result of radiation exposure, principally from radiotherapy for an underlying thoracic malignancy. Depending on the dose received and the extent of radiation, symptoms range from a mild cough to chronic respiratory insufficiency and pulmonary hypertension. The diagnosis mandates a thorough clinical and imaging workup in order to confirm the diagnosis.
Radiation pneumonitis (often described as the initial event in radiation-induced lung injury) is not uncommon after the use of radiotherapy for treatment of malignant diseases located in the thorax   . The clinical presentation, although possessing a very wide spectrum of symptoms, depends on three main factors - the amount of radiation received by the patient (rare cases have been described after receiving < 20 Gy, while 40 Gy virtually always causes symptoms), the volume of the irradiated lung and the dose fractionation  . Certain cytotoxic drugs, when combined with radiotherapy, have also been implicated in the pathogenesis of radiation pneumonitis, such as bleomycin  . In milder cases, radiation pneumonitis is manifested as a subtle cough accompanied by chest discomfort that may spontaneously resolve after some time . On the other hand, dyspnea, a prominent nonproductive cough, and fever that progress to severe respiratory decline and cyanosis are typical for more severe cases  . Symptoms can appear after only 1 month in the case of profound radiation injury, whereas up to 6 months might pass before first symptoms are observed in individuals who were exposed to lower doses   . Regardless of the severity, the vast majority of patients develop progressive fibrosis of the lungs, which may lead to chronic respiratory insufficiency, portal hypertension (as a result of congestion), hepatomegaly, orthopnea, and a significant impairment in the overall quality of life  .
The initial signs of radiation pneumonitis, particularly in milder cases, have often been misinterpreted or misdiagnosed . For this reason, a thorough clinical investigation is mandatory in order to make a correct diagnosis. Physicians must obtain a meticulous patient history that will reveal an underlying malignant disease for which radiation therapy was recently used, and such findings must point toward radiation pneumonitis. Furthermore, a detailed physical examination, with an emphasis on lung auscultation and palpation of the abdomen (as liver tenderness is observed in severe cases) , may provide additional evidence to pursue the diagnosis. In addition to lung-function tests and evaluation of pulse oximetry, imaging studies should be employed. In the acute setting, plain radiography of the lungs can detect ground-glass opacities or lung consolidation at the site of irradiation as early as few weeks after radiotherapy  . Less common, but still important findings are the presence of a crazy paving pattern (opacities located at the ground-glass appearing areas), a reversed halo sign (a central opacity encircled by dense consolidation), pleural and pericardial effusions, as well as bronchiectasis   . Atelectasis and fibrosis, as well as their extension beyond the field of radiation, is seen in profound radiation injury  . Because the radiographic signs are not uniform across all individuals, computed tomography (CT), particularly contrast-enhanced CT, is often recommended over chest X-rays, as it provided a better view of the structural changes of the lungs   . Fluorodeoxyglucose-positron emission tomography (FDG-PET) is also recommended by some authors .