| disease | Radiation Pneumonitis |
| alias | Radiation Pneumonitis |
Radiation pneumonitis is an inflammatory reaction caused by injury to normal lung tissue within the radiation field following radiotherapy for lung cancer, breast cancer, esophageal cancer, cervical malignancy with cachexia, or other thoracic malignancies. Mild cases may be asymptomatic, with inflammation resolving on its own; severe cases can lead to extensive pulmonary fibrosis, resulting in impaired respiratory function or even respiratory failure.
bubble_chart Etiology
The occurrence and severity of radiation pneumonitis are closely related to the radiation method, dose, area, and speed. It is believed that the threshold dose is 2500–3000 rad within 3 weeks. According to clinical statistics from Zhongshan Hospital of Shanghai Medical University, when the dose is less than 2000 rad within 6 weeks, pneumonitis rarely occurs. However, when the dose exceeds 4000 rad, the incidence of pneumonitis increases significantly, and doses exceeding 6000 rad invariably lead to radiation pneumonitis. The larger the radiation field, the higher the incidence. Large-area radiation causes more severe lung injury than localized radiation, and faster radiation speeds increase the likelihood of lung injury. Other influencing factors include poor individual tolerance to radiation, pre-existing lung conditions such as pneumonia, chronic bronchitis, chronic obstructive pulmonary disease, and repeat radiation therapy, all of which can promote the development of radiation pneumonitis. Certain chemotherapy drugs may also exacerbate lung reactions to radiation. The elderly and children have poorer tolerance to radiation therapy.
bubble_chart Pathological Changes
Acute pathological changes often occur 1-2 months after radiotherapy, and in some cases may not appear until half a year after treatment. These changes manifest as injury to pulmonary blood vessels, particularly capillaries, leading to congestion, edema, and cellular infiltration. There is also reduced regeneration of type II alveolar cells, lymphatic dilation, and the formation of hyaline membranes. Acute changes may resolve spontaneously but often result in pulmonary connective tissue hyperplasia, fibrosis, and hyaline degeneration. The chronic phase typically occurs more than 9 months after radiotherapy, characterized by extensive alveolar fibrosis, lung contraction, thickening and sclerosis of capillary membranes, luminal narrowing or obstruction, leading to increased pulmonary vascular resistance and pulmonary arterial hypertension. The pleura may also thicken due to inflammation and fibrosis. Metaplasia of bronchiolar mucosal epithelium and secondary pulmonary infections can accelerate radiation-induced fibrosis.bubble_chart Clinical Manifestations
Mild cases may be asymptomatic. Symptoms typically appear 2–3 weeks after radiotherapy, often including irritative, dry cough accompanied by dyspnea, palpitations, and chest pain, with no fever or low-grade fever, occasionally high fever. Dyspnea progressively worsens as pulmonary fibrosis intensifies, and respiratory infections can easily exacerbate respiratory symptoms. Difficulty swallowing occurs if radiation esophagitis develops. If radiation injures the ribs, causing fractures, localized tenderness is evident. Physical examination reveals atrophy and hardening of the skin in the irradiated area, with dry and wet rales and friction rubs audible in the lungs. Extensive and severe pulmonary fibrosis may eventually lead to pulmonary hypertension and cor pulmonale, manifesting corresponding signs.
bubble_chart Auxiliary Examination
Changes in pulmonary function: Both radiation pneumonitis and fibrosis cause restrictive ventilatory dysfunction, reduced lung compliance, accompanied by a decreased ventilation/perfusion ratio and diminished diffusion capacity, leading to hypoxia. Sometimes, chest X-rays may not yet show abnormalities, while pulmonary function tests already reveal changes.
X-ray findings: In most cases, lung shadows appear one month after radiation therapy is discontinued. During the acute phase, diffuse patchy opacities appear in the irradiated lung fields, with faintly visible reticular shadows, resembling bronchopneumonia or pulmonary edema. The extent of the lesions corresponds to the radiation field on the chest surface. Chronic pulmonary fibrosis develops, presenting as linear or mass-like contraction or localized atelectasis. There is extensive adhesion of the mediastinal pleura and pericardium, with mediastinal shift toward the affected side, elevation of the ipsilateral diaphragm, and collapse of the thorax.
Based on the history of radiotherapy, dry cough, progressive dyspnea, and inflammatory or fibrotic changes on chest X-ray, a diagnosis can be made. However, it should be differentiated from the progression of lung tumors and metastatic tumors to avoid misdiagnosis and continued radiotherapy, which can lead to death. Irradiation of the bronchial mucosal epithelium often causes cellular metaplasia, which should be carefully distinguished from cancer cells.
bubble_chart Treatment Measures
To prevent the occurrence of radiation pneumonitis, it is essential to strictly control the total radiation dose, the distribution of single doses, and the size of the irradiation field. For breast cancer radiotherapy, tangential projection is preferred to minimize lung injury. During radiotherapy, patients should be closely monitored for respiratory symptoms and elevated body temperature. If pneumonia is detected on X-ray, radiotherapy should be immediately discontinued.
