TY - JOUR T1 - Evaluation of 3′-Deoxy-3′-<sup>18</sup>F-Fluorothymidine for Monitoring Tumor Response to Radiotherapy and Photodynamic Therapy in Mice JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1754 LP - 1758 VL - 45 IS - 10 AU - Masahiro Sugiyama AU - Harumi Sakahara AU - Kengo Sato AU - Norihiro Harada AU - Dai Fukumoto AU - Takeharu Kakiuchi AU - Toru Hirano AU - Eiji Kohno AU - Hideo Tsukada Y1 - 2004/10/01 UR - http://jnm.snmjournals.org/content/45/10/1754.abstract N2 - 3′-Deoxy-3′-18F-fluorothymidine (18F-FLT) has been suggested as a new PET tracer for imaging tumor proliferation. We investigated the use of 18F-FLT to monitor the response of tumors to radiotherapy and photodynamic therapy (PDT) in mice. Methods: C3H/He mice bearing an SCCVII tumor were treated with single-dose x-ray irradiation of 20 Gy. Tumor uptake was examined for 18F-FLT, 3H-thymidine (3H-Thd), 18F-FDG, and 14C-deoxyglucose (14C-DG) at 6 h, 12 h, 24 h, 3 d, and 7 d after radiotherapy. BALB/c nu/nu mice bearing a HeLa tumor were treated with PDT. Tumor uptake was examined for the 4 tracers at 24 h after PDT. Expression of proliferating cell nuclear antigen (PCNA) was determined in untreated and treated tumors. Results: In the biodistribution study, considerable uptake of 18F-FLT was observed in both tumor types. Tumor volumes decreased to 39.3% ± 22.4% at 7 d after radiotherapy. The PCNA labeling index was reduced in x-ray–irradiated tumors (control, 53.2% ± 8.7%; 6 h, 38.5% ± 5.3%; 24 h after radiotherapy, 36.8% ± 5.3%). 18F-FLT uptake in tumor expressed as the percentage of the injected dose per gram of tumor (%ID/g) decreased significantly at 6 h and remained low until 3 d after radiotherapy (control, 9.7 ± 1.2 %ID/g; 6 h, 5.9 ± 0.4 %ID/g; 24 h, 6.1 ± 1.3 %ID/g; 3 d after radiotherapy, 6.4 ± 1.1 %ID/g). 18F-FDG uptake tended to gradually decrease but a significant decrease was found only at 3 d (control, 12.1 ± 2.7 %ID/g; 6 h, 13.3 ± 2.3 %ID/g; 24 h, 8.6 ± 1.8 %ID/g; 3 d after radiotherapy, 6.9 ± 1.2 %ID/g). PDT resulted in a reduction of the PCNA labeling index (control, 82.0% ± 8.6%; 24 h after PDT, 13.5% ± 12.7%). Tumor uptake of 18F-FLT decreased (control, 11.1 ± 1.3 %ID/g; 24 h after PDT, 4.0 ± 2.2 %ID/g), whereas 18F-FDG uptake did not decrease significantly after PDT (control, 3.5 ± 0.6 %ID/g; 24 h after PDT, 2.3 ± 1.1 %ID/g). Changes in the uptake of 18F-FLT and 18F-FDG were similar to those of 3H-Thd and 14C-DG, respectively. Conclusion: In our model system, changes in 18F-FLT uptake after radiotherapy and PDT were correlated with those of 3H-Thd and the PCNA labeling index. The decrease in 18F-FLT uptake after treatments was more rapid or pronounced than that of 18F-FDG. Therefore, 18F-FLT may be a feasible PET tracer for monitoring response to therapy in oncology. ER -