The tumor volume delineation is a key step for the improvement of precision of tumor radiotherapy.The multimodality image fusion between CT and MRI,or PET and CT,or PET and MRI can obviously compensate for lower tumor boundary display definition caused by single modality image for many tumor eases.In addition,the lung breathing also will cause the displacement of tumor contour boundary,thus it is necessary to make tracking analysis on its contour boundary change for all dynamic CT image series,and to obtain maximum tumor displacement boundary.Before real field radiotherapy,these tumor volume and displacement boundary obtained by the multimodality image fusion and dynamic CT image tracking analysis should be verified by static 3D DRR verifying image and real time conformal beam field,and not be out of the range of real time eonformal beam field for accurate radiotherapy.