en Radiation Biology Radiation Biology تحقيق بديع Original Research <b>Background:</b> Radiotherapy is an established therapeutic modality for prostate cancer. Resveratrol, a natural antioxidant, has been shown to inhibit carcinogenesis and to block the process of tumor initiation and progression. No data is available on the response of cellular spheroid to Reseveratol. In this study we have examined the effect of Resveratol on the radiation response of human prostate cell line DU145 in monolayer and spheroid cultures. <b>Materials and Methods:</b> Radiosensitivity was assessed using viability and colony formation assay. Apoptosis and necrosis were assessed using acridine orange/ ethidium bromide double staining. <b>Results:</b> The colony formation assay did not show any significant radio-sensitizing effect, but apoptosis assay showed significant radio-sensitizing effect of Resveratol on DU145 cells grown as monolayer. In the spheroid cells the results of apoptosis test were not significant and corresponded closely to the result of survival curve. <b>Conclusion:</b> While Resveratol could sensitize DU145 cells in monolayer to ionizing radiation, it did not have any effect on sensitivity of cells cultured in spheroid cultures.<b> Iran. J. Radiat. Res., 2012 10(3‐4): 177‐181 </b> Resveratrol, X-ray irradiation, multicellular spheroid, radioresistance, apoptosis. 177 181 http://ijrr.com/browse.php?a_code=A-10-1-441&slc_lang=en&sid=1 M.S. Nezamtaheri 790031947532846003083 790031947532846003083 No S. Khoei 790031947532846003084 790031947532846003084 No A.R. Nikoofar 790031947532846003085 790031947532846003085 No B. Goliaei goliaei@ibb.ut.ac.ir 790031947532846003086 790031947532846003086 Yes