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内容記述 |
[Purpose] In-beam PET is a practical technique for verifying the beam range in particle therapy, as positron emitters are produced along the beam path through nuclear fragmentation reactions. To enable 3D in-beam PET, we developed a human-scale OpenPET system, which features a full-ring geometry with a cylindrical shape cut by two parallel oblique planes, creating an open space that allows the treatment beam to pass through. This study aimed to evaluate the inter-fraction consistency of in-beam OpenPET images in carbon-ion therapy and to assess the potential of the system for treatment verification and quality assurance.[Methods] The OpenPET system was installed in the treatment room of the Heavy Ion Medical Accelerator in Chiba (HIMAC). Patients with head and neck cancer who underwent several treatment fractions under the same treatment plan were enrolled. As the OpenPET system is dedicated to horizontal irradiation, vertical irradiation was performed first. Subsequently, the OpenPET gantry was positioned at the isocenter using a rail system to ensure reproducible placement. PET data acquisition was conducted during horizontal irradiation and continued for 10 minutes after beam-off. Inter-fraction consistency was quantitatively evaluated using gamma-index analysis, which compares two images based on spatial and intensity agreement.[Results] Gamma-index evaluation showed high pass rates across all treatment fractions, indicating no significant variation among in-beam PET images acquired under identical irradiation plans. The results confirmed stable image characteristics, indicating that no significant inter-fractional differences affecting the beam range, such as patient setup and physiological variations, occurred.[Conclusion] Consistent in-beam OpenPET images across fractions demonstrate beam range stability in repeated carbon-ion therapy sessions. These findings support the feasibility of using in-beam OpenPET as a quality assurance tool for verifying treatment reproducibility and monitoring anatomical changes during the treatment course. |
