PURPOSE:External beam radiation therapy (EBRT) alone for early stage, medically inoperable non-small cell lung cancer (MILC) can produce local disease control and sometimes cure. We have previously reported that higher EBRT doses result in improved disease control and, for patients with tumors > or =3.0 cm, improved survival. This report describes the impact of dose escalation with endobronchial brachytherapy boost during or following EBRT upon local disease control. METHODS AND MATERIALS:Medical records of 404 patients with MILC treated with radiotherapy alone were reviewed. Thirty-nine patients received a planned endobronchial brachytherapy boost during or following a course of EBRT. A matched-pair analysis of disease control and survival was performed by matching each brachytherapy patient to 2 EBRT patients from a reference group of the remaining patients. RESULTS:Endobronchial brachytherapy boost significantly improved local disease control over EBRT alone (58% vs. 32% at 5 years). The local control benefit for brachytherapy was found to be limited to patients with T(1-2) disease or tumors < or =5.0 cm. Among these patients treated with endobronchial boost, EBRT doses of > or =6500 cGy were necessary to optimize local disease control. No overall survival differences were observed at 3 years. Excess toxicity with brachytherapy was not observed. CONCLUSION:Endobronchial brachytherapy boost enhances local disease control rates in MILC treated with EBRT. Local control outcome is optimized when radical EBRT doses are used in conjunction with brachytherapy.