Objective:To compare the percentages of lung volume receiving ≥ 20 Gy（V20） and ≥ 30 Gy（V30） between interstitial brachytherapy（ISBT） and intensity-modulated radiotherapy（IMRT） in advanced lung cancer patients with mediastinal lymph node metastasis

and to investigate the feasibility of using ISBT for the lung tumor plus IMRT for mediastinal lymph nodes to reduce the lung dose. Methods:The target volumes of lung tumor and mediastinal lymph nodes were delineated on the CT images of a human phantom. The ISBT plan and IMRT plan were made for each target volume

and the IMRT plan was made for the mediastinal lymph node target volume. Comparison of lung V20 and V30 was made. The relationship between V20 difference and the size of target volume was analyzed. Results:Lung V20 and V30 were lower in the regimen involving ISBT plan

and there were significant differences in lung V20 and V30 between the two regimens（P < 0.05）

except in lung V20 for the lung target volumes of the same size（P > 0.05）. The V20 and V30 differences of the two regimens decreased with the increase in the size of target volume. Conclusion:ISBT for the lung tumor plus IMRT for mediastinal lymph nodes is feasible to reduce the lung dose

and it may be limited by the tumor size.