Presentation Information
[16p-S2_202-7]Compton Imaging of Ac-225 using GAGG-SiPM based pixel detectors
〇(M2)HAO GUO1, Boyu Feng1, Ayaka Otsuka1, Kenji Shimazoe1, Seiichi Ohta1 (1.Tokyo Univ.)
Keywords:
Medical radiation detection and measurement,Imaging & Image processing
Actinium-225 (Ac-225) is emerging as a key radionuclide for targeted alpha therapy (TAT) because of its high linear energy transfer and potent cell-killing capability, enabling promising outcomes for treating disseminated and micrometastatic disease. Quantitative imaging of Ac-225 and its daughters is essential for preclinical pharmacokinetic studies, treatment planning, and dosimetry; however, conventional gamma imaging is challenging due to low photon yields, multiple emissions, and the severe sensitivity loss imposed by mechanical collimation in SPECT. Compton imaging offers an attractive alternative by replacing collimation with electronic event reconstruction, potentially improving sensitivity for low-activity Ac-225 studies while maintaining energy flexibility for emissions from daughter nuclides (notably 218 keV from 221Fr and 440 keV from 213Bi). In this work, we developed a compact Compton camera based on HR-GAGG scintillator pixel detectors coupled to SiPM arrays. The system adopts a two-layer geometry (thin scatter layer and thick absorber layer), where each layer is instrumented with pixelated GAGG-SiPM modules (pixel pitch: 3.2 mm, pixel size: 2.5 mm×2.5 mm) and read out using a time-over-threshold–based front-end to extract energy and timing for list-mode event building.We demonstrate Ac-225 imaging performance using (i) point-source measurements and (ii) preclinical phantom imaging. Using energy windows centered at 218 keV and 440 keV, Compton reconstruction successfully localized the sources and resolved phantom structures. The reconstructed spatial resolution (image-space FWHM) was 6.18 mm at 440 keV under a source-to- scatter detector distance of 43.7mm. These results support the feasibility of GAGG-SiPM Compton imaging for sensitive, low-activity Ac-225 studies and provide a pathway toward practical quantitative imaging for TAT-related preclinical research.