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Abstract
Recently, 225Ac has received considerable attention for its use in targeted alpha therapy because it has a relatively long half-life and yields four more alpha-particles from the daughter nuclides. The performance evaluation should separately assess the distribution of 225Ac and 213Bi because daughter nuclides, including 213Bi, can cause renal toxicity, which may hinder the widespread use of 225Ac for targeted alpha therapy. In this study, we describe and validate a spectrum decomposition method for dual-isotope imaging of 225Ac and 213Bi using an alpha imaging detector. We implemented an experiment to demonstrate the feasibility of using the alpha imaging detector to obtain distribution images using therapeutic amounts of 225Ac. In addition, we designed and conducted a Monte Carlo simulation under realistic conditions based on the experimental results to evaluate the spectrum decomposition method for dual-isotope imaging. The alpha imaging detector exhibited a detection efficiency of 18.5% and an energy resolution of 13.4% at 5.5 MeV. In the simulation, the distributions of 225Ac and 213Bi were obtained in each region with a relative error of 5%. The results of this study confirmed the feasibility of the dual-isotope imaging method for discriminating alpha-emitters using small amounts of 225Ac.

Fig. Kidney Fusion image of 225Ac and 213Bi generated using the distribution images in Figure 9. In the fusion image, 225Ac and 213Bi are shown in red and green, respectively. Note, the region composed of a mixture of two nuclides is shown in the mixture of the colours

Affiliations

Jong-Guk Kim 1, Guna Kim 2, Hyun Su Lee 3, Byoungsoo Kim 3, Il-Han Lim 3, Kwangil Kim 3, Kyochul Lee 3
1Korea Institute of Radiological and Medical Sciences, Seoul, 01812, Republic of Korea. Electronic address: jgkim@kirams.re.kr.
2Radiation Safety Management Division, Korea Atomic Energy Research Institute, Daejeon, 34057, Republic of Korea.
3Korea Institute of Radiological and Medical Sciences, Seoul, 01812, Republic of Korea.