Ponente
Descripción
Introduction
Compton cameras are a promising tool in radiopharmaceutical therapy (RPT) treatment assessment and dosimetry, where gamma cameras perform sub-optimally due to the high energies of the emitted photons and low activities. The IRIS group is developing MACACO, a LaBr3-based Compton camera, for this application. The prototype MACACO III has been successfully used to visualize I-131 and Ac-225 [1,2] in phantoms. The latest prototype, MACACO III+, was tested at CIC biomaGUNE using a mouse phantom with several organs filled with I-131 and live mice injected with [I-131]NaI. The images were compared with those obtained using a commercial pre-clinical SPECT system. Simulations of a mouse with a realistic biodistribution of [Ac-225]Ac-DOTA were performed to test the viability of using MACACO III+ for imaging Ac-225 in small animals.
Methods
MACACO III+ features two detector planes, the first one composed of a single detector with 25.8 mm x 25.5 mm x 5 mm crystal size, and the second plane comprising four such detectors. The system was tested at CIC biomaGUNE with a mouse phantom, filling different combinations of the brain, heart, kidney and bladder in 45 minute acquisitions. Two living mice injected with 1.20 MBq and 2.16 MBq of [I-131]NaI were imaged during 30 minutes. The mouse phantom and the living mice were also imaged in a γ-CUBE SPECT system from Molecubes for 3 hours in a tomographic acquisition.
Simulations were performed using GATE and a digital 3D mouse phantom containing 25 kBq of Ac-225, with activity per organ based on data from biodistributions in mice injected with [Ac-225]Ac-DOTA [3], including a tumor of realistic size and uptake located in the brain.
Results/Discussion
Measurements of the mouse phantom filled with I-131 resulted in images comparable to those obtained using the γ-CUBE. When four organs were filled, the brain, heart, bladder and individual kidneys were clearly distinguishable. Images of the two live mice acquired using MACACO III+ are also similar to those obtained with the γ-CUBE, as can be seen in the attached figure. Here, I-131 uptake can be clearly identified in the thyroid gland as well as in the bladder and stomach. Form the simulation studies, Ac-225 accumulation can be clearly visualized in the tumor and the individual kidneys.
Conclusion
The MACACO Compton camera developed by the IRIS group successfully imaged I-131 distributions in a mouse phantom and living mice for the first time and shows great promise for imaging Ac-225, as shown by realistic simulations. Images of I-131 distributions were obtained with lower acquisition times and of similar quality compared to those obtained using a commercial pre-clinical SPECT. Future studies will be aimed at imaging other isotopes in live animals, in particular Ac-225.
References
[1] J Roser et al. 2024 Phys Medica 132:104928
[2] K. Brzezinski et al, Talk at 2024 IEEE NSS MIC, Tampa, USA, 26 Oct - 2 Nov 2024.
[3] M. Rodak et al. 2022 Mol Cancer Ther. 21(12) 1835–1845
