Cellular dosimetry of beta emitting radionuclides-antibody conjugates for radioimmunotherapy

The choice of optimal radionuclides for radioimmunotherapy depends on several factors, especially the radionuclide and antibody. The dosimetric characteristics of a non-internalizing and an internalizing monoclonal antibody (MAb) labeled with beta emitting radionuclides were investigated. Using Geant4-DNA Monte Carlo simulation, we carry out dosimetric calculations for different subcellular distributions of beta-emitting radionuclides; 131I, 177Lu, 64Cu, 186Re and 153Sm. The dependency of theradialdose profiles on the energy spectra of   electrons (beta particles and Auger and internal conversion electrons) and also their relative yield of emission is clear. The highest difference between the radionuclides tested was observed when the activity was localized in the nucleus. There was not considerable difference in the nucleus dose when radionuclides were localized in cytoplasm and over the cell membrane. There is a very significant increase in the dose deposited to the nucleus if 153Sm localized at the nucleus. Although subcellular localization of activity isn’t a critical factor for beta emitting radionuclides, but the use of internalizing MAbs leads to an increase in nucleus dose and to the killing of single cells in addition to the tumors.