Author: Go Akamatsu, Hiroaki Ikawa, Yuma Iwao, Han Gyu Kang, Masashi Koto, Hideyuki Mizuno, Akram Mohammadi, Makoto Shinoto, Minoru Tajiri, Hideaki Tashima, Chie Toramatsu, Taiga Yamaya 👨🔬
Affiliation: National Institutes for Quantum Science and Technology 🌍
Purpose: In-beam positron emission tomography (PET), in which positron emitters produced through fragmentation reactions are visualized, is a practical method for range verification in particle therapy. As a PET system for such in-beam use, the OpenPET, which has an aslant ring geometry to pass the beam through to the patient, has been developed. In contrast to a conventional dual-panel PET system, which is mainly dedicated to two-dimensional imaging, OpenPET enables three-dimensional imaging with high sensitivity. The aim of this study was to apply a prototype of the OpenPET for visualization of an irradiation field in carbon-ion therapy.
Methods: The OpenPET prototype, which was positioned on retractable rails, was installed in the Heavy Ion Medical Accelerator in Chiba (HIMAC). Head and neck cancer was selected, and for total 16 fractions, in-beam PET measurement was performed 4 times each in the fractions of 1-4, 5-8, 9-12 and 13-16. Because the OpenPET prototype was designed only for horizontal irradiation, vertical irradiation was performed first without using OpenPET. Then after moving the OpenPET to the isocenter along the rails, OpenPET measurement was performed during the horizontal irradiation and continued for 10 min after the end of the irradiation. The gamma analysis was applied to compare images between different fractions obtained with the same treatment plan.
Results: The RBE-weighted dose delivered for each fraction was 1.3 Gy for the vertical and 2.7 Gy for the horizontal irradiation. For the tolerance value ∆D=3% for the difference in the voxel value and the tolerance value ∆d=6 mm for the spatial distance, the gamma pass rate of 99.4%, which was high enough, was obtained between the 2nd and the 8th fractions.
Conclusion: In the first clinical trial of OpenPET targeting head and neck cancer, feasibility of OpenPET, which confirmed the same dose prescription between different fractions, was shown.