Radiation-induced injury in the "nonirradiated" lung.

An unqualified answer to the above question is "yes". A qualified response, however, requires that the word, "nonirradiated", be defined. A truly nonirradiated lung represents the pulmonary parenchyma that is not exposed to any type or amount of radiation. Currently, there is sufficient scientific basis to consider that this nonirradiated normal lung parenchyma can suffer injury caused by radiation therapy aimed at malignant disease. There have been several reports of pathological processes occurring outside the field of radiation, including the contralateral lung [1±5]. These abnormalities have been demonstrated by a diffuse increased gallium uptake on lung scan, lymphocytosis in the bronchoalveolar lavage (BAL) fluid of nonirradiated lung [5], and a histological pattern consistent with bronchiolitis obliterans-organizing pneumonia (BOOP) in biopsy specimens from nonirradiated lung. BOOP, however, remains less well known among clinicians. The type of injury sustained by the lung that is not exposed to radiation is different from either the acute radiation-induced pneumonitis or the chronic radiationinduced pulmonary fibrosis. These two well known types of lung pathology indicate a direct physical insult of radiation on the lung. The "classic" radiation pneumonitis has been recognized in patients receiving radiation treatment for nonpulmonary (i.e. breast) as well as pulmonary malignancies [6, 7]. In most cases, radiographic findings are confined to the field of radiation. However, bilateral lymphocytic alveolitis develops in both lung fields in most patients after unilateral breast irradiation [5]. When external beam radiation therapy is contemplated for the treatment of cancers of the lung, breast, oesophagus, or other organs adjacent to or in the vicinity of the lungs, great effort is undertaken to avoid radiation injury to lung parenchyma uninvolved in the neoplastic process. While this effort is theoretically sound, it is practically impossible to prevent normal pulmonary parenchyma (that is closely adjacent to the radiated area) from some exposure to radiation. This normal lung exposed to direct radiation thus suffers radiation injury. Furthermore, normal pulmonary parenchyma in the path of the tangential radiation field can also suffer injury. Some have argued that "radiation scatter" over areas away from those intended can cause radiation lung injury. All of these represent direct radiation insult to the lungs. The effects are well-recognized in clinical medicine as acute radiationinduced lung injury and chronic radiation-induced lung fibrosis. The pulmonary damage caused by radiation in these entities is dependent on the total dosage, fractionation protocol, dose rate, type of radiation used, and the volume of lung exposed to the radiation.