Evaluation of the usefulness of ^<99m>Tc-MIBI scintigraphy and positron emission tomography to analyze the radiotherapeutic effects in breast cancer models

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【Introduction】 Radiotherapy is a principal treatment in primary and metastatic breast cancer. The aim of this study was to investigate the difference of distribution of ^<99m>Tc-MIBI and deoxyglucose (DG) before and after irradiation in breast cancer models. We also investigated the correlation between microvessel density and ^<99m>Tc-MIBI uptake.【Materials and Methods】 Double-tracer macroautoradiography (ARG) images were prepared with ^<99m>Tc-MIBI and ^<14>C-DG in transplanted models using 3 mouse breast cancer cell lines (FM3A, MM48 and Ehrlich). The radiotherapeutic effects were monitored by measuring tumor burden, uptake and ARG finding using ^<99m>Tc-MIBI and ^<18>F-FDG.Microvessel density was quantified by immunohistochemical staining for CD34 and compared with ARG using ^<99m>Tc-MIBI.【Results】 Three tumors showed different growth rates and radiosensitivities, but ^<99m>Tc-MIBI uptake did not correlate significantly with the growth rates. Compared with ^<14>C-DG, ^<99m>Tc-MIBI accumulated more in cancer cells and less in infiltrating fibroblasts and macrophages in all tumor models. Microvessel density in tumor tissue correlated significantly with ^<99m>Tc-MIBI uptake on ARG.【Conclusion】 Accumulation of ^<99m>Tc-MIBI in cancer cells is preferential and can be used as a sensitive marker to examine the response of radiotherapy. Angiogenesis seems to enhance accumulation of ^<99m>Tc-MIBI in tumors. These characteristics may be favorable for tumor imaging using ^<99m>Tc-MIBI.