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内容記述 |
At the National Institutes for Quantum Science and Technology, helium, carbon, oxygen, and neon ion beams are utilized together in multi-ion therapy to enhance the therapeutic efficacy of charged-particle therapy. When accelerated ions traverse a medium, a fraction will undergo nuclear interactions, some of which, in turn, produce positron-emitting nuclei. This study investigates the accuracy of ion beam range determination using the annihilation photons emitted from the nuclei measured with an in-house online PET system (OpenPET). A polymethyl methacrylate phantom was irradiated separately with un-scanned helium, carbon, oxygen, and neon ion beams to 1.5-Gy doses at the Bragg peak. Annihilation photons were measured with OpenPET after irradiation. Each irradiation was simulated using the Particle and Heavy Ion Transport code System (PHITS) to obtain the predicted annihilation photon distributions. The range of beams in the phantom was determined by comparing measured and simulated planar-integrated annihilation photon distributions (PIADs) using maximum likelihood estimation method. The measured PIADs showed good agreement with the simulated PIADs for carbon, oxygen, and neon ions. However, discrepancies were observed for helium ions, likely due to uncertainties in the cross-section data used in PHITS. The range was determined within an accuracy of 2 mm for four ion species for the measurement time longer than 3 minutes. |
