Magnetic Particle Imaging for Quantitative Evaluation of Tumor Response to Magnetic Hyperthermia Treatment Combined with Chemotherapy Using Cisplatin

This study was undertaken to evaluate the tumor response to magnetic hyperthermia treatment (MHT) combined with cisplatin (MHT+CDDP) using magnetic particle imaging (MPI). Colon-26 cells were implanted into the backs of mice. When the tumor volume exceeded approximately 100 mm3, the mice were divided into control, MHT, CDDP, and MHT+CDDP groups. In the CDDP and MHT+CDDP groups, CDDP (5 mg/kg) was injected intraperitoneally. In the MHT+CDDP group, magnetic nanoparticles [250 mM (14.0 mg Fe/mL) Resovist®]were directly injected into the tumor one hour after CDDP administration, and MHT was performed for 20 min using an alternating magnetic field. In the MHT group, only MHT was performed after the injection of Resovist®. In the MHT+CDDP and MHT groups, MPI images were obtained using our MPI scanner immediately before, immediately after, and 3, 7, and 14 days after MHT. After the MPI studies, we drew a region of interest (ROI) on the tumor in the MPI image and calculated the average and maximum MPI values and the number of pixels within the ROI. In all groups, the relative tumor volume growth (RTVG) was calculated from (V-V0)/V0, where V0 and V were the tumor volumes immediately before and after treatment, respectively. The RTVG value in the MHT+CDDP group was significantly lower than that in the MHT group 3 to 14 days after MHT. It was also significantly lower than that in the CDDP group at 4 to 11 days except at 6 and 9 days after treatment. The average and maximum MPI values normalized by those immediately before MHT in the MHT+CDDP group were significantly higher than those in the MHT group 3 days after MHT. Our results suggested that MPI is useful for quantitatively evaluating tumor response to MHT combined with chemotherapy.