Cellular and Multicellular Dosimetry of two copper radioisotopes: 67Cu and 64Cu

Radiopharmaceuticals are usually distributed nonuniformly inside tissues, since only a fraction of the cells are actually labeled. Labeled and unlabeled cells often receive different absorbed doses depending on the distribution pattern at the cellular and subcellular level and the characteristics of the emitted radiations. Both 67Cu and 64Cu radionuclides have nuclear decay features which make them suitable for diagnostic and therapeutic applications in nuclear medicine. However, 64Cu-based therapy is commonly considered advantageous if the radionuclide is incorporated inside cell nuclei, as its Auger electron emission component may cause a very high level of DNA damage. In this work, the MIRDCell software was used to assess the doses due to radioactive decays of a uniform distribution of 67Cu and 64Cu in tumour models represented as isolated spheres of water density. Besides, the dependence of the dose to cell nuclei on the subcellular distribution of radionuclides, cluster cell dimension and percentage of labeled cells were also investigated by modelling these spheres as cluster of cells. The results of this study demonstrate that, if xxCu is localized into the cell nucleus, the dose to the nucleus in isolated single tumor cells and very small cell clusters is larger for 64Cu compared to 67Cu, but this advantage is lost in larger clusters simulating micro-metastases.