Abstract
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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 carbon ion irradiation under hypoxic condition.
Methods Colorectal cancer cell line Colon26 cells were used. Cells were cultured under 1% oxygen concentration for 24 h, and then were treated with 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 h after irradiation, Cells were also treated with X-ray irradiation as a control.
Results In carbon ion 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 0.5y and 1 Gy on day 3 (P<0.01 and P<0.001) and lasted to day 4 (both P<0.001) in the carbon ion treated cells. On the other hand, 18F-FLT cell uptake was significantly lower at 5 and 10 Gy in the carbon ion group (both P<0.05) and at 10 Gy in the X-ray group (P<0.05).
Conclusions The carbon ion irradiation was more effective than X-ray irradiation under hypoxic condition. The reduction of 18F-FLT uptake after carbon irradiation was more rapid than the change of cell viability at 5 and 10 Gy. Therefore, 18F-FLT is a promising tracer for monitoring early responses of cancer to carbon ion irradiation under hypoxic condition.