Evaluation of Therapeutic Effects of Radiotherapy during Treatment of Lung Adenocarcinoma in Mice with Positron Emission Tomography Imaging of 18F-FLT and 18F-FDG

Purpose: To assess the role of 3'-deoxy-3'-¹⁸F-fluoro-thymidine (¹⁸F-FLT) and 2'-deoxy-2'-¹⁸F-fluorodeoxy- glucose (¹⁸F-FDG) positron emission tomography (PET) imaging in the evaluation of the therapeutic effects of radiotherapy during treatment of lung adenocarcinoma.
Methods: Eighteen mice with lung adenocarcinoma were randomly divided into 2 groups; each group was randomly paired and evenly divided into three smaller groups, namely, A, B and C. Group A served as the control group without any treatment; mice in group B were received radiotherapy in sites of tumor. A single dose of 2000 cGy, 6MV x-ray was used in this experiment; mice in group C also received radiotherapy at sites of tumors two days before the experiment using the same procedure and dose as group B. Micro PET imaging was taken after intravenous injection of ¹⁸F-FLT and ¹⁸F-FDG through the mice’s tail.
Results: The intake ratio of ¹⁸F-FLT and ¹⁸F-FDG was much higher at the tumor sites. After radiotherapy, ¹⁸F-FLT uptake was significantly lower than that of the control group (p < 0.05), while there was no obvious change of ¹⁸F-FDG uptake. There was a significant decrease in T/NT value of FLT PET imaging group 24 and 48 h after radiotherapy; a significant difference could be seen, compared with that before radiotherapy (p < 0.05).
Conclusion: Change in ¹⁸F-FLT uptake induced by radiotherapy is more sensitive than that of ¹⁸F-FDG. Intake of ¹⁸F-FLT is lowered more significantly after radiotherapy than that of ¹⁸F-FDG, and this can serve as evidence that ¹⁸F-FLT is an effective tracer to monitor the therapeutic effect of radiotherapy on malignant tumors.

Keywords
3'-deoxy-3'-¹⁸F-fluoro-thymidine; 2'-deoxy-2'-¹⁸F-fluoro-deoxy-glucose; Radiotherapy; Positron Emission Tomography imaging; Cell proliferation; Lung adenocarcinoma