Assessment of radiotherapeutic effects on experimental tumors using ¹⁸F-2-fluoro-2-deoxy-D-glucose

The purpose of this study is to evaluation the effect of tumor volume and radiotherapy on the uptake of ¹⁸F-2-fluoro-2-deoxy-D-glucose (¹⁸FDG). The tumor models used were mouse mammary carcinoma MM48, FM3A, and rat hepatoma AH109A. Results were expressed as an ¹⁸FDG uptake ratio. This was the ratio of irradiated tumor uptake of ¹⁸FDG to unirradiated tumor uptake. The total tumor uptake was expressed as ¹⁸FDG uptake ratio multiplied by relative tumor volume. Following 20 Gy irradiation of the radioresistant tumor (MM48), the ¹⁸FDG uptake ratio was found to be unchanged, whereas in radiosensitive tumors (FM3A) the ¹⁸FDG uptake ratio was 0.37, the relative tumor volume was 0.31, and the calculated total tumor uptake was 0.11 on the eighth day after irradiation. The total tumor uptake was lower than the relative tumor volume. AH109A began to regrow after ten Gy irradiation, accompanied by elevated uptake of ¹⁸FDG on the seventh day. These results suggest that the ¹⁸FDG uptake by tumor is a good marker of radiotherapeutic effects as well as relapses of cancers and is more sensitive than morphological methods.