Abstract
1035
Objectives: The objective of this study was to investigate whether 3'-deoxy-3'-[18F]fluorothymidine (18F-FLT) could monitor early responses of malignant tumors to proton 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 were 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-FLT cell uptake experiment was assessed at 24 hr after irradiation, Cells were also treated with X-ray irradiation as a control.
Results: In proton and X-ray treated cells, a significant difference in the cell number on day 2, compared with controls (cells without irradiation), was observed in the group at 5 and 10 Gy (all P < 0.001) and this significant difference persisted until day 4 after irradiation (all P < 0.001). In addition, significant differences in the cell number were observed in the groups at 1 Gy on day 3 (P<0.001) and lasted to day 4 (P<0.05) in the proton treated cells. In the proton group, 18F-FLT cell uptake was significantly lower at 10 Gy (P<0.001) and significantly higher at 0.5Gy and 1 Gy (P<0.05 and P<0.01). 18F-FLT cell uptake was significantly higher at 1 Gy in the X-ray group (P<0.05).
Conclusion: The proton irradiation was more effective than X-ray irradiation under hypoxic condition. The reduction of 18F-FLT uptake after proton irradiation was more rapid than the change of cell viability at only 10 Gy. In addition, there were no significant differences at 5 and 10 Gy compared with control in the X-ray group. These results suggested that the time point (24 h after irradiation) of addition of 18F-FLT was not adequate in hypoxic condition, although 18F-FLT is a promising tracer for monitoring early responses of cancer to proton irradiation. Now 18F-FLT cell uptake study at 48 hr after irradiation is ongoing. Research Support: This study was partially supported by a research fund of the Wakasa Wan Energy Research Center and JSPS KAKENHI Grant Number 24249065.