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Background: In the treatment of osteosarcoma, the chemotherapeutic effect influences decisions regarding the surgical margin, continuation of chemotherapy, and choice of anticancer drugs for further chemotherapy. Therefore, it is necessary to evaluate the response to chemotherapy in the middle of the chemotherapy course. In this study, we investigated the use of Tc-hexakis-2-methoxyisobutyl-isonitrile (Tc-MIBI) scintigraphy in evaluating the response to chemotherapy of patients with osteosarcoma in comparison with Tl scintigraphy and angiography. Methods: A total 45 patients with osteosarcoma were examined using Tc-MIBI scintigraphy, Tl scintigraphy, and angiography to evaluate their response to chemotherapy. The percentage reduction in the uptake ratios (ΔUR) calculated as 100 × [(prechemotherapy value − postchemotherapy value)/prechemotherapy value] were compared with histological assessments. Similarly, changes in tumor vascularity assessed by angiograms were compared with histological assessments. On the angiographic findings, the results were classified as complete response (CR), partial response (PR), no change (NC), or progressive disease (PD). On the images, ΔUR in Tc-MIBI ≥ 30% and ΔUR in Tl ≥ 30% were classified as responder, as were CR and PR in angiograms. The therapeutic effect was assessed by histopathological examination of the resected specimens. The tumors of poor responders showed less than 90% necrosis, whereas the tumors of good responders showed 90% or more necrosis. Results: Sensitivity, specificity, and accuracy were 73.9, 84.2, and 78.6%, respectively, for Tc-MIBI (κ = 0.57); 80.0, 61.1, and 72.1%, respectively, for Tl (κ = 0.42); and 91.7, 35.0, and 65.9%, respectively for angiography (κ = 0.28). Conclusion: Tc-MIBI could be effectively used to predict the final response to chemotherapy of osteosarcoma. [ABSTRACT FROM AUTHOR]