Dosimetry assessment of theranostic Auger-emitting radionuclides in a micron-sized multicellular cluster model: A Monte Carlo study using Geant4-DNA simulations.

The present work is aimed at improving the multicellular dosimetry of several Auger radionuclides of interest for targeted cancer therapy, including 99mTc, 111In, 123I, 125I, and 201Tl. For this purpose, using the Geant4-DNA Monte Carlo code, a cluster of 13 similar spherical cells with a hexagonal packed arrangement was modeled, and the mean absorbed doses per unit cumulated activity (S-values) were calculated by considering two target←source configurations, cell←cell and nucleus←nucleus. The obtained ratios of cross-dose to self-dose S-value in terms of the distance between the source and target regions were evaluated and also compared to those estimated by the Medical Internal Radiation Dose (MIRD) method. Besides, the contribution of the Coster-Kronig, Auger and internal conversion electrons to the S-values was provided for each radionuclide. According to the results, it can be concluded that in contrast to self-absorption, the cross-absorption due to the Auger-emitters has not a significant role in the total energy deposition within a cell in the cluster.