Abstract: The lung is a parallel organ,which is radiation sensitive. It is necessary to strictly control the dose to normal lung tissue during chest radiotherapy. By comparing and analyzing the DVH map data obtained after the definition of two different lung ttissue, it is found that when a large tumor in the lung is defined, the tumor volume should be subtracted from the definition of normal lung tissue in order to more objectively reflect the functional lung ttissue intake and guide the delineation of normal lung tissue, so that lung injury can be predicted more accurately.

Key words: Lung tumor, Intensity-modulated radiation therapy, Normal lung tissue