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 radio therapy in 15 asymptomatic patients were compared with findings in a g roup of patients with clinical radiation pneumonitis. Measurements: Hi story, physical examination, chest radiograph, quantitative gallium lu ng scanning, respiratory function tests, bronchoalveolar lavage, and l avage lymphocyte subset analysis. Results: After irradiation, lavage l ymphocytes increased significantly (34.5% versus 46.8%; P = 0.01) in t he 17 patients studied prospectively. There was an associated reductio n in vital capacity (102.5% versus 95.5%; P = 0.04). Comparison of res ults in patients before treatment, after treatment without clinical pn eumonitis, and after treatment with clinical pneumonitis showed a dram atic increase in total lymphocytes after irradiation (6.3 versus 9.4 v ersus 35.2 million, respectively; P = 0.005), particularly in those wi th clinical pneumonitis. Only in those with clinical pneumonitis was t his accompanied by an increase in the gallium index (3.7 versus 3.4 ve rsus 9.0, respectively; P < 0.001). Vital capacity was also progressiv ely 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%, respecti vely; P = 0.003). No statistical differences existed between irradiate d 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 irradi ation; this is more pronounced in patients developing clinical pneumon itis. These findings suggest that radiotherapy may cause a generalized lymphocyte-mediated hypersensitivity reaction.