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Abstract: Assessment of treatment response in acute leukemia is routinely performed after therapy via bone marrow biopsy. We investigated the use of positron emission tomography (PET) for early assessment of treatment response in patients with acute myeloid leukemia (AML), using the proliferation marker 3′-deoxy-3′-[18F]fluoro-l-thymidine (FLT). Eight adult AML patients receiving induction chemotherapy underwent whole-body FLT PET/CT scans acquired at different time points during therapy. Patients who entered complete remission (CR) exhibited significantly lower FLT uptake in bone marrow than those patients with resistant disease (RD). In bone marrow, mean and maximum standardized uptake values were 0.8, 3.6 for CR and 1.6, 11.4 for RD, p <0.001. FLT PET results for CR and RD patients were independent of assessment time point, suggesting that FLT PET scans acquired as early as 2 days after chemotherapy initiation may be predictive of clinical response. This pilot study suggests that FLT PET imaging during induction chemotherapy may serve as an early biomarker of treatment response in AML. [Copyright &y& Elsevier]

Abstract: Spatial organization of tumor phenotype is of great interest to radiotherapy target definition and outcome prediction. We characterized tumor phenotype in patients with cancers of the oropharynx through voxel-based correlation of PET images of metabolism, proliferation, and hypoxia. Methods: Patients with oropharyngeal cancer received 18F-fluorodeoxyglucose (FDG) PET/CT, 18F-fluorothymidine (FLT) PET/CT, and 61Cu-diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) PET/CT. Images were co-registered and standardized uptake values (SUV) were calculated for all modalities. Voxel-based correlation was evaluated with Pearson’s correlation coefficient in tumor regions. Additionally, sensitivity studies were performed to quantify the effects of image segmentation, registration, noise, and segmentation on R. Results: On average, FDG PET and FLT PET images were most highly correlated (R FDG:FLT =0.76, range 0.53–0.85), while Cu-ATSM PET showed greater heterogeneity in correlation to other tracers (R FDG:Cu-ATSM =0.64, range 0.51–0.79; R FLT:Cu-ATSM =0.61, range 0.21–0.80). Of the tested parameters, correlation was most sensitive to image registration. Misregistration of one voxel lead to ΔR FDG =0.25, ΔR FLT =0.39, and ΔR Cu-ATSM =0.27. Image noise and reconstruction also had quantitative effects on correlation. No significant quantitative differences were found between GTV, expanded GTV, or CTV regions. Conclusions: Voxel-based correlation represents a first step into understanding spatial organization of tumor phenotype. These results have implications for radiotherapy target definition and provide a framework to test outcome prediction based on pretherapy distribution of phenotype. [Copyright &y& Elsevier]