Basic Research On ¹⁸F-FLT PET/CT Imaging In Efficacy Evaluation Of Radiotherapy For Lung Adenocarcinoma

Objective:To evaluate the effect of 18F-FLT PET/CT imaging to assess the prognosis of lung adenocarcinoma after radiotherapy, and contrast with 18F-FDG which is used in clinic frequently.Methods:Cell experiments:Use different of doses of X-rays to irradiate the cultured human lung adenocarcinoma cell line A549 and the irradiation doses were 0Gy,2Gy, 5Gy,8Gy,10Gy and 15Gy respectively. Then observed the A549 cell morphological changes under the microscope at different times after irradiation. And using y RIA counter to detect the change of A549 cell uptake ability to 18F-FLT or 18F-FDG 1h,2h,4h,6h,8h,12h,24h and 48h later in sequence. Collecting the different groups cells at different times after irradiation in centrifuge tube, then discarding the supernatant after centrifugation, adding 1 milliliter of 95% ethanol in centrifuge tube to fix the A549 cells. The cells were stored in refrigerator at 4℃for more than one day. Flow cytometry was applied to detect the A549 cell cycle changes after irradiation, and Mod Fit Software was uesd to analyze the cell cycle results. Use MTT colorimetric assay to calculate the cell growth inhibition rate under the same conditions on the A549 cell with different doses of radiotherapy 24h and 48h later. Animal experiments:First of all, to establish nude mice model with A549 human lung adenocarcinoma cell lines. Mice model receive 18F-FLT and 18F-FDG PET/CT imaging before the radiotherapy, after radiotherapy 3 days,1 week,2 weeks and 4 weeks. We analysed SUVmax and T/NT value respectively. Radiation doses were 0Gy,2Gy,5Gy,8Gy, 10Gy and 15Gy. We measured the tumor volume every other day. At last, we killed the nude mice for the tumor. Use immunohistochemistry to detect the expression of Ki-67 in every slice. Statistical software SPSS 15.0 was applied to analysis data. We analysis correlation between A549 cell uptake 18F-F LT or F-FDG ability and cell growth inhibition rate or cell cycle S phase proportion respectively. We also analysed correlation between T/NT value and Ki-67 expression in correspondence slice.Results:1. A549 cell growth inhibition rate grows complying with increase of the irradiation dose and times after radiotherapy.2. We can observe G2/M phase cell block peak in different of levels of A549 cell after radiation.3. The ability of A549 cell uptaking F-FDG is stronger than F-FLT after radiotherapy. There was negative correlation between the ability of A549 cells uptakes 18F-FLT 18F-FDG and growth inhibition rate after radiotherapy 24h and 48h.4. The ability of A549 cell uptaking 18F-FLT is correspond with the change of the proportion of S phase cell, but not the 18F-FDG.5. Not only the 18F-FDG PET/CT, but also the 18F-FLT PET/CT can show the mice tumor clearly and correctly before irradiation. There are more 18F-FDG uptaked than 18F-FLT in tumor. Both 18F-FDG and 18F-FLT can distinguish malignancy correctly. 6. The diversification of Ki-67 expression is greater after radiotherapy. Ki-67 expression in the low-dose groups(0,2,5 Gy) increased and then decreased after radiotherapy, but high-dose groups(8,10,15Gy) increased all the time. 7. T/NT values of 18F-FLT PET/CT imaging related with Ki-67 expression, but not the 18F-FDG, and the inflammation caused by radiation made the F-FDG PET/CT imaging in the 10Gy and 15Gy groups perform badly. 8. Ki-67 expression changed earlier than tumor size, and there were no correlation between them.9.18F-FLT performs better than 18F-FDG in the diagnosis of inflammation, and false positives can be seen in 18F-FDG PET/CT imaging.Conclusions:It is proved that 18F-FLT PET/CT imaging can reflect the effect of radiotherapy on lung adenocarcinoma both in vitro experiments and animal studies. F-FLT is not influenced by the glucose metabolism, but it has a greater tumor-specific than 18F-FDG. The ability of A549 cell uptaking 18F-FLT corresponds with the change of the proportion of S phase cell, but not the 18F-FDG. The T/NT value of 18F-FLT PET/CT imaging related with Ki-67 expression, but not the 18F-FDG, and the inflammation caused by radiation made the 18F-FDG PET/CT imaging in the lOGy and 15Gy groups; performe badly.18F-FLT performs better than 18F-FDG in the diagnosis of inflammation aspect, and false positives can be seen in 18F-FDG PET/CT imaging.