Radiation pneumonitis: a possible lymphocyte-mediated hypersensitivity reaction

* Objective: To determine if unilateral thoracic irradiation results in a lymphoid alveolitis in both irradiated and unirradiated lung fields. * Design: A prospective, nonrandomized study. * Patients: Women receiving postoperative radiotherapy for carcinoma of the breast were evaluated both before and 4 to 6 weeks after radiotherapy. Findings after radiotherapy in 15 asymptomatic patients were compared with findings in a group of patients with clinical radiation pneumonitis. * Measurements: History, physical examination, chest radiograph, quantitative gallium lung scanning, respiratory function tests, bronchoalveolar lavage, and lavage lymphocyte subset analysis. * Results: After irradiation, lavage lymphocytes increased significantly (34.5% versus 46.8%; P = 0.01) in the 17 patients studied prospectively. There was an associated reduction in vital capacity (102.5% versus 95.5%; P = 0.04). Comparison of results in patients before treatment, after treatment without clinical pneumonitis, and after treatment with clinical pneumonitis showed a dramatic increase in total lymphocytes after irradiation (6.3 versus 9.4 versus 35.2 million, respectively; P = 0.005), particularly in those with clinical pneumonitis. Only in those with clinical pneumonitis was this accompanied by an increase in the gallium index (3.7 versus 3.4 versus 9.0, respectively; P < 0.001). Vital capacity was also progressively reduced (102.5% versus 96.9% versus 76.7%, respectively; P = 0.04), as was diffusing capacity (98.6% versus 91.4% versus 72.6%, respectively; P = 0.003). No statistical differences existed between irradiated and unirradiated sides of the chest in either lavage or gallium lung scan studies. * Conclusion: in most patients, a lymphocytic alveolitis develops in both lung fields after strictly unilateral thoracic irradiation; this is more pronounced in patients developing clinical pneumonitis. These findings suggest that radiotherapy may cause a generalized lymphocyte-mediated hypersensitivity reaction.
Lymphocyte-mediated hypersensitivity may be responsible for radiotherapy-induced pneumonitis. Pneumonitis is an inflammation of the lungs. Early acute pneumonitis develops in 5% to 15% of patients who undergo radiation therapy of the chest. Levels of lymphocytes, which are a type of white blood cell, were measured before and after radiation therapy in 17 women who had surgery for breast cancer. The percentage of lymphocytes obtained following irrigation of the lungs increased from 34.5% to 46.8%, and 13 of the women developed lymphocytosis, which is an excess of lymphocytes. Although the women had radiotherapy on only one lung, lymphocytosis developed to a similar degree in both lungs. Seven of the women developed radiation pneumonitis. The percentage of white blood cells was 43.5% in women who did not develop pneumonitis compared with 67.6% among women who did develop pneumonitis. The total lymphocyte count was 9.4 million in women who did not develop pneumonitis compared with 35.2 million among women who did develop pneumonitis.