ABSTRACT
<p><b>BACKGROUND AND OBJECTIVE</b>Monitoring the therapeutic effects of radiotherapy for nasopharyngeal carcinoma (NPC) is critical to providing individualized treatment. This in-vivo study was initially designed to evaluate the therapeutic effect of radiotherapy using 18F-fluorodeoxyglucose positron emission tomography with computed tomography (18F-FDG PET-CT) imaging.</p><p><b>METHODS</b>18F-FDG PET-CT imaging was performed on all of the 10 nude mice bearing NPC xenografts before radiotherapy, and early-phase and delayed-phase PET-CT images were performed on 7 of the 10 mice. All mice were randomly divided into either a control group or a radiotherapy group. The 5 mice in the control group were immediately killed after the imaging and pathology were performed. After receiving radiotherapy of 12 Gy, 5 animals in the radiotherapy group were given 18F-FDG PET-CT imaging on days 2, 4, and 6, and then were killed for pathologic evaluation. Regions of interest (ROI) technology was used to measure the tumor target/non-target (T/NT) ratio and the volume of the tumors.</p><p><b>RESULTS</b>The average T/NT ratios of early- and delayed-phase imaging were 1.806 +/- 0.532 and 1.777 +/- 0.597, respectively, with no significance (P > 0.05). For the radiotherapy group, the average T/NT ratios for 18F-FDG PET-CT before radiotherapy, and on days 2, 4, and 6 after radiotherapy, were 1.735 +/- 0.466, 1.818 +/- 0.396, 1.096 +/- 0.101, and 0.604 +/- 0.108, respectively, The tumor volumes were (1.48 +/- 0.27) cm3, (1.57 +/- 0.31) cm3, (1.59 +/- 0.31) cm3 and (1.60 +/- 0.29) cm3, respectively. The average T/NT ratios of day 6 after radiotherapy and the other time points were significant (P < 0.05). The average death ratio of the tumor cells was (93.00 +/- 7.42)% after 6 days of post-radiotherapy.</p><p><b>CONCLUSIONS</b>18F-FDG PET-CT imaging can be used for the early assessment of radiotherapeutic effect of NPC in vivo. Day 6 after radiotherapy may be an appropriate time point for the imaging. However, the T/NT ratio measurement of delayed-phase imaging might make no sense for the diagnosis of NPC.</p>