[en] Objective: The aim of this study was to assess the value of fusion SPECT perfusion and CT images acquired separately at 2 time-points in evaluating regional lung function of patients with stage III non-small cell lung cancer (NSCLC). Methods: Thirty-two patients with untreated stage III NSCLC under- went pulmonary function test (PFT), CT and SPECT imaging. Two series of images were registered by software fusion based on external markers by Philips Pinnacle3 planning treatment system. The SPECT/CT fusion images were graded by comparing lung perfusion defect with the area of radiological abnormality. Grade 0: no lung perfusion defect in the area of radiological abnormality. Grade 1: the area of lung perfusion defect was similar to the size of radiological abnormality. Grade 2: the area of lung perfusion defect was bigger than that of radiological abnormality, and extended to 1 pulmonary lobe. Grade 3: the area of lung perfusion defect exceeded 1 pulmonary lobe. Statistically significant difference was evaluated by Pearson χ²-test using SPSS 13.0 software. Results: In 32 patients with stage III NSCLC, 31 patients had lung perfusion defects. There were 13 patients with grade 1, 8 with grade 2, 10 with grade 3. There was statistically significant difference between central lung cancer and peripheral lung cancer (χ²=10.49.5, P<0.05); 8 patients had PFT abnormality. There was also statistically significant difference between the positive rate of SPECT/CT fusion images and PFT [96.9% (31/32) vs25.0%(8/32), χ²=34.724, P<0.05]. Conclusion: The fusion of SPECT lung perfusion and CT images acquired separately at 2 different time-points is a feasible technique for assessing the regional lung function of patients with stage III NSCLC, thereby offering more in- formation for surgical planning, prediction of postoperative lung function and optimization of radiation treatment plans. (authors)