Early changes of F-18 flt uptake after irradiation of tumor in animal model

F-18 Fluorothymidine (FLT) has been introduced as a new radiotracer for imaging proliferating cell, but its potential for monitoring radiotherapy has not been fully investigated. The aim of of this study was to evaluate early changes of FLT uptake after irradiation of tumor in animal model and microPET. Nine C3H/HeN mice with SCC-VII tumors in their right shoulders were divided into three groups according to radiation dose (0 Gy, 10 Gy and 20 Gy, n=3 in each group). At 1 hr after i.p. injection of 3.7 MBq of FLT, sequential microPET (Concord, R4) images were obtained on the day before radiation (day0), day1 and day2 after radiation of tumor. Quantification was done using ASIProtm. Tumor to background uptake (T/B) ratios were measured using ROIs in sum of three consecutive slices of coronal view with slice thickness of 0.085 cm. Maximum T/B ratios in three groups (0 Gy, 10 Gy and 20 Gy) were 2.6±0.3, 3.1±1.0, 2.6±0.1 on day 0, and showed 5.3%, 59.1%, 57.5% decrease on day 1 and 22.7%, 54.2%, 59.5% decrease on day 2, respectively. Mean T/B ratios in three groups were 2.4±0.3, 2.7±0.5, 2.6±0.2 on day 0, and showed 6.5%, 52.8%, 50.4% decrease on day 1 and 11.6%, 47.4%, 53.9% decreased on day 2, respectively. In irradiated groups, maximum and mean T/B ratios were significantly decreased on day 1 and day 2 after irradiation (p < 0.0000), and significantly lower than control group. However, there was no significant difference between 10 Gy and 20 Gy groups. In control (0 Gy) group, the T/B ratio was not changed on day 1, but it was decreased on day 2 (p=0.0093). The change of FLT uptake on 1 day after irradiation reflected early radiation induced changes of tumor, and it may be used for imaging early tumor response to radiotherapy