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Background: To determine the optimal timing and analytic method of 2-deoxy-2-[(18)F]fluoro-D-glucose positron emission tomography (PET) imaging during fractionated radiotherapy (RT) to predict tumor control., Methods: Ten head neck squamous cell carcinoma xenografts derived from the UT-14-SCC cell line were irradiated with 50 Gy at 2 Gy per day over 5 weeks. Dynamic PET scans were acquired over 70 minutes at baseline (week 0) and weekly for seven weeks. PET data were analyzed using standard uptake value (SUV), retention index (RI), sensitivity factor (SF), and kinetic index (Ki)., Results: Four xenografts had local failure (LF) and 6 had local control. Eighty scans from week 0 to week 7 were analyzed. RI and SF after 10 Gy appeared to be the optimal predictors for LF. In contrast, SUV and Ki during RT were not significant predictors for LF., Conclusion: RI and SF of PET obtained after the first week of fractionated RT were the optimal methods and timing to predict tumor control.

Purpose: To investigate the metabolic information provided by (18)F-fluorodeoxyglucose-positron emission tomography (FDG-PET) during the early response of head-and-neck squamous cell carcinoma (HNSCC) xenografts to radiotherapy (RT)., Methods and Materials: Low-passage HNSCC cells (UT14) were injected into the rear flanks of female nu/nu mice to generate xenografts. After tumors grew to 400-500 mm(3), they were treated with either 15 Gy in one fraction (n = 18) or sham RT (n = 12). At various time points after treatment, tumors were assessed with 2-h dynamic FDG-PET and immediately harvested for direct histological correlation. Different analytical parameters were used to process the dynamic PET data: kinetic index (Ki), standard uptake value (SUV), sensitivity factor (SF), and retention index (RI). Tumor growth was assessed using the specific growth rate (SGR) and correlated with PET parameters using the Pearson correlation coefficient (r). Receiver operating characteristic (ROC) and the area under the ROC curve (AUC) were used to test PET parameters for their ability to predict for radiation necrosis and radiation change., Results: Tumor growth was arrested for the first 20 days after RT and recovered thereafter. Histologically, radiation change was observed in the peripheral regions of tumors between days 7 and 23 after RT, and radiation necrosis were observed in the central regions of tumors between days 7 and 40. Ki provided the best correlation with SGR (r = 0.51) and was the optimal parameter to predict for early radiation necrosis (AUC = 0.804, p = 0.07). SUV(30 min) was the strongest predictor for late radiation necrosis (AUC = 0.959, p = 0.004). Both RI(30-60 min) and SF(12-70 min) were very accurate in predicting for radiation change (AUC = 0.891 and 0.875, p = 0.009 and 0.01, respectively)., Conclusions: Dynamic FDG-PET analysis (such as Ki or SF) may provide informative assessment of early radiation necrosis or radiation change of HNSCC xenografts after RT., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Purpose: Glioblastoma multiforme (GBM) is an aggressive tumor that typically causes death due to local progression. To assess a novel low-dose radiotherapy regimen for treating GBM, we developed an orthotopic murine model of human GBM and evaluated in vivo treatment efficacy using micro-positron-emission tomography/computed tomography (microPET/CT) tumor imaging., Methods: Orthotopic GBM xenografts were established in nude mice and treated with standard 2-Gy fractionation or 10 0.2-Gy pulses with 3-min interpulse intervals, for 7 consecutive days, for a total dose of 14 Gy. Tumor growth was quantified weekly using the Flex Triumph (GE Healthcare/Gamma Medica-Ideas, Waukesha, WI) combined PET-single-photon emission CT (SPECT)-CT imaging system and necropsy histopathology. Normal tissue damage was assessed by counting dead neural cells in tissue sections from irradiated fields., Results: Tumor engraftment efficiency for U87MG cells was 86%. Implanting 0.5 × 10(6) cells produced a 50- to 70-mm(3) tumor in 10 to 14 days. A significant correlation was seen between CT-derived tumor volume and histopathology-measured volume (p = 0.018). The low-dose 0.2-Gy pulsed regimen produced a significantly longer tumor growth delay than standard 2-Gy fractionation (p = 0.045). Less normal neuronal cell death was observed after the pulsed delivery method (p = 0.004)., Conclusion: This study successfully demonstrated the feasibility of in vivo brain tumor imaging and longitudinal assessment of tumor growth and treatment response with microPET/CT. Pulsed radiation treatment was more efficacious than the standard fractionated treatment and was associated with less normal tissue damage., (Copyright © 2011 Elsevier Inc. All rights reserved.)