Abstract
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Objectives: he objective of this study was to investigate whether 18F-FDG and 18F-FLT could monitor early responses of malignant tumors to charged particle irradiation under hypoxic condition.
Methods: Colorectal cancer cell line Colon26 cells were used. Cells were cultured under 1% oxygen concentration for 24 hr, and then were respectively treated with proton and carbon ion irradiation. Irradiation doses were0, 0.1, 0.5, 1, 5 and 10 Gy. From day 1 to day 4 after irradiation treatment, the cell number was measured. The 18F-FDG and 18F-FLT cell uptake experiment was assessed at 26 and 50 hr after irradiation. Cells were also treated with X-ray irradiation as a control.
Results: In proton treated cells, compared with control group (0 Gy group), a significant difference in the cell number was observed in the group at 1, 5 and 10 Gy at day 4 after irradiation. In carbon ion treated cells, there were significant differences from 0.5 Gy irradiated group. In X-ray treated cells, there were significant differences in 5 and 10 Gy irradiated groups. In cell uptake study at 26 hr after irradiation, the uptake of 18F-FDG was significantly decreased in 10 Gy group in X-Ray irradiation. Moreover, the uptake of 18F-FLT was increased in 0.5 and 1 Gy groups in proton irradiation, although it was decreased in 5 and 10 Gy groups in carbon ion and X-ray irradiation. Therefore, changes in the uptake of both 18F-FDG and 18F-FLTdid not reflect changes in cell numbers. In cell uptake study at 50 hr after irradiation, the uptake of 18F-FDG was decreased in 5 and 10 Gy groups in proton and carbon ion irradiation. On the other hand, the uptake of 18F-FLT was decreased in 0.1 ~ 10 Gy groups in carbon ion irradiation, in 1 ~ 10 Gy groups in proton irradiation, and in 5 and 10 Gy groups in X-ray irradiation. Thus, changes in the uptake of 18F-FLT reflected changes in cell numbers, although changes in the uptake of 18F-FDG did not.
Conclusions: 18F-FLT is a promising tracer for monitoring early responses of cancer to charged particle irradiation under hypoxic condition. Research Support: This study was partially supported by a research fund of the Wakasa Wan Energy Research Center and JSPS KAKENHI Grant Number 24249065.