e23100 Background: PET imaging with 18F-fluorothymidine (18F-FLT) can potentially be used to identify tumor subvolumes for selecting dose escalation in radiation therapy. The aim of this study was to monitor tumor cell proliferation and repopulation during fractionated radiotherapy and investigated the spatial concordance of tumor cell proliferation and repopulation with 18F-FLT tracer uptake. Methods: Mice bearing A549 xenograft tumors were assigned to 5 different irradiated groups (3f/6d, 6f/12d, 9f/18d, 12f/24d and 18f/36d) with 2 Gy/fractions and non-irradiated group. Serial 18F-FLT micro PET scans were performed at different time points, the maximum of standard uptake value (SUVmax) were measured to detect the feasible time of tumor repopulation during irradiation. Ex vivo images of the spatial pattern of intratumor 18F-FLT uptake and Ki-67 labeling index (LI) were obtained from thin tumor tissue sections. A layer-by-layer comparison between SUVmax and Ki-67 LI results, including the thresholds at which maximum overlap occurred between FLT-segmented areas and areas of active cell proliferation, were conducted to evaluate the spatial imaging pathology correlation. Results: The SUVmax were observed decreases in the 3f/6d group (P = 0.000), compared to these for non-irradiated tumors. However, it was significantly increased in the 6f/12d later, and then gradually reduced with treatment time prolonged again after 6f/12d group. Proliferation changes on pathology imaging at 6f/12d were also confirmed. Significant correlations were found between the SUVmax and Ki-67 LI of all ROIs in each in vitro tumor of cell proliferation group (Ps < 0.001). Similar results were also found in each tumor of accelerated repopulation group (Ps < 0.001). Furthermore, both of the mean ORRs were more than 50% in all layer of the tumor cell proliferation and accelerated groups. Regions of high-intensity 18F-FLT uptake in the autoradiographs exhibited prominent staining for Ki-67. Conclusions: 18F-FLT PET may be a promising imaging surrogate of tumor proliferative response to fractionated radiotherapy and might help make adaptive radiation oncology treatment plan.
Spatial Concordance of Tumor Proliferation and Accelerated Repopulation from Pathologic Images to 3′-[18F]Fluoro-3′-Deoxythymidine PET Images: a Basic Study Guided for PET-Based Radiotherapy Dose Painting