A retrospective analysis of patients with inoperable, Stage III non-small cell lung carcinoma presenting with malignant airway occlusion and treated with endobronchial brachytherapy boost prior to radical radiotherapy is reported. Of the 102 patients treated with endobronchial brachytherapy between October 1986 and January 1991, 22 were newly diagnosed, biopsy-proven Stage IIIA (14/22) or IIIB (8/22) non-small cell carcinoma with > 80% endoscopically demonstrated airway occlusion of the carina (1/22), mainstem bronchus (10/22) or lobar bronchus (11/22). Fifteen patients had complete lung or lobar atelectasis. Poor performance status (KPS < 70% in 13/22) and/or weight loss (> 10% in 9/22) rendered these patients ineligible for multi-institutional trials. Endobronchial boost was delivered using low dose rate (20 Gy at 2 cm) or high dose rate brachytherapy (16 Gy in 4 fractions over 2 days at 2 cm). Following a 10-14 day post-endobronchial period to allow for reaeration, patients underwent additional external beam radiotherapy (60 Gy in 30 fractions). Of the 15 patients with atelectasis, 6/15 (40%) reaerated completely, 4/15 (27%) partially, and 5/15 (33%) failed to reaerate. A new method, called "sequential volume integration" was used on the pre- and post-endobronchial films to analyze sparing of thoracic volume from external beam radiation as a consequence of reaeration. Patients with complete reaeration required 47% less and those patients with partial reaeration required 25% less ipsilateral thoracic volume radiation. There was a tend toward improved survival in reaerators (36 weeks) as compared to non-reaerators (24 weeks).