量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum and Radiological Science and Technology.
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The OpenPET geometry is our original idea to visualize a physically opened space between two detector rings. One of the targets is in-beam PET, which is a method for in situ monitoring of charged particle therapy. The OpenPET is expected to be the first practical 3D geometry, while conventional trials using positron cameras are basically limiting to 2D imaging with low statistics. In the last year, we have developed the small prototype and carried out the initial in-beam tests in the Heavy Ion Medical Accelerator in Chiba (HIMAC). In this paper, we carried out the detailed experiments to show range resolution performance.
Methods:
The OpenPET prototype (two detector rings of 110 mm diameter separated by a gap of 42 mm) was positioned so that the beam passed through the gap. For usual carbon (12C) beam irradiation, the activity of positron emitters produced through fragmentation reactions is generally low, in addition to the theoretical difference between the dose distribution and positron emitter distribution. Instead of the 12C beam, therefore, we used a 11C radioactive beam as an incident beam directly. A PMMA phantom was placed in the center of the FOV, and irradiated along radial direction by the 11C / 12C pencil beam (~30 Gy).
Results:
For the 11C irradiation, PET images directly corresponding to the distribution of primary particles were obtained with more than ten times higher activity concentration compared with the 12C irradiation. Especially, a 3 mm difference in the range was detectable only from in-beam measurement data, while additional off-beam measurement was required for the 12C beam.
Conclusion:
We showed feasibility of PET image-guided carbon ion therapy. Our next work will include exploration of performance limitation for the reduced irradiation dose.
In-beam imaging performance of the small OpenPET prototype for carbon ion therapy
