Objective After studying the change rule of the blood brain barrier(BBB) permeability, to provide the imaging evidence of radiotherapy effect evaluation and choose optimal chance of chemotherapy during whole brain radiotherapy (WBRT) in patients with brain metastasis by 99mTc DTPA brain SPECT. Methods 19 patients with brain metastasis who undergone WBRT by 60Co were studied. All patients underwent 99mTc DTPA brain SPECT before, during WBRT. The total counts radio of the tumor and contralateral brain (T/N) before and during WBRT(20 Gy) was calculated. Results 1) The average T/N before WBRT and during WBRT in 32 tumors was 1.892?1.094 and 2.167?1.637 respectively. (t =2.433,P