SU-E-CAMPUS-J-06: Development of a Tumor Blood Flow Measurement System for Proton Therapy Patients

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Purpose: To develop a tumor blood flow rate measurement system utilizing positron emission after proton therapy for potential evaluation of the efficacy of radiotherapy, concurrent chemotherapy and/or antiangiogenesis therapy of proton therapy patients. Method: Daily proton treatment generates positron emission nuclei, i.e., 15O, 13N and 11C inside the treated volume of patients. In-room measurement of activities of 15O as a function of time right after proton treatment can directly measure tumor blood flow rate due to the biological washout characteristics. A pair of NaI2 detectors and coincidence detection electronics were obtained. The NaI2 detectors were mounted on a modified C-arm for good axial alignment and flexible isocentric rotation. The detector energy spectrum was calibrated using 60Co, 137Cs and 22Na sources. The energy window was set for 511 keV peaks. Current system is not optimized for collimation and shielding. The system performance was evaluated using 18F-FDG. Proton irradiated water and/or ice were also measured for positron emission activity and the acquired data were analyzed. Detector shielding and collimation is under construction. IRB approval for proton patient blood flow rate measurement was obtained for evaluation of their tumor blood flow rates and changes over treatment course. Results: The C-arm based detector platform demonstrated precise alignment and great flexibility for different treatment sites. The 18F-FDG decay measurement using the system showed the measured half life is within 16s of the theoretical value. Activity measurement of proton irradiated water and ice showed about 10s half life difference between the measured and theoretical value. This was potentially due to the activation inside the water/ice container and lack of detector collimation and shielding. Conclusions: A non-invasive in-room tumor blood flow rate measurement system for proton therapy patients is under development. The preliminary data is reported. American Cancer Society Chris DiMarco Institutional Research Grant

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