A Pilot Study of the Utility of 18F-FLT-PET and Diffusion-Weighted MRI for Surgical Planning, Radiotherapy Target Delineation, and Treatment Response Evaluation in Ewing Sarcoma Patients

PRIMARY OBJECTIVES: I. Establish correlation between 18F-FLT positron emission tomography (PET) activity, apparent diffusion coefficients (ADC) values from diffusion-weighted magnetic resonance imaging (DW-MRI), fludeoxyglucose F 18 (18F-FDG) PET activity, magnetic resonance imaging (MRI) contrast enhancement, and pathologic response for Ewing sarcoma. II. Assess the efficacy of detecting therapy induced changes in 18F-FLT PET uptake and ADC from DW-MRI for more accurately predicting local control, event-free survival, and overall survival as compared to standard prognostic factors (e.g. change in tumor size). III. Compare radiotherapy target volume delineation with pre- and post-chemotherapy 18F-FLT PET and DW-MRI information to delineation with pre-chemotherapy conventional MRI to determine role of advanced imaging in radiotherapy treatment planning for Ewing sarcoma. SECONDARY OBJECTIVES: I. Establish correlation between 18F-FLT PET activity, ADC values from DW-MRI, 18F-FDG PET activity, MRI contrast enhancement, and biomolecular assays for Ewing sarcoma. II. Determine imaging thresholds to discriminate between viable and necrotic tumor, as established through pathologic correlations. III. Assess efficacy of advanced imaging for more accurately guiding biopsy targeting by comparing planned targeting with standard (MRI contrast enhancement) vs. advanced imaging (18F -FLT PET and DW-MRI). IV. Compare post-treatment response assessment with 18F-FLT PET and DW-MRI vs. 18F-FDG PET to determine whether 18F-FLT PET and ADC information is more accurate than 18F-FDG PET for distinguishing between necrosis and non-specific inflammation immediately following treatment. V. Estimate potential reduction in acute and late side effects based on modified radiation therapy (RT) treatment volumes with pre- and post-chemotherapy 18F-FLT PET and DW-MRI information as compared to volumes delineated with pre-chemotherapy conventional MRI. VI. Evaluate automatic image segmentation techniques for 18F-FLT PET and DW-MRI, comparing against biopsy determined imaging thresholds and expert Nuclear Medicine and MR Radiologist contours. OUTLINE: Patients undergo 18F-FLT PET, 18F-FDG PET, and DW-MRI the week prior to induction therapy, within one week after the completion of induction therapy, the week prior to RT (for patients that received surgery), and within 1 week of completion of RT. After completion of study intervention, patients are followed up every 3 months for 1 year and then every 6 months for up to 4 years.