Fig. 1

A Monte Carlo-simulated energy spectrum for \(^{223}\text {Ra}\)-based \(\alpha\)-RPT SPECT in 2-D. The activity map was a single-voxel 2-D phantom and the attenuation map considered is shown in Fig. 3b. The Monte Carlo simulation process is as described in “Agreement between path-based modeling approach and MC simulation” section except for including multiple order of scatters. The three photopeak energy windows are shown in color. (EW1 = 68–102 keV, EW2 = 123–184 keV, EW3= 243–297 keV)