The aim of this study was to build a simulation framework to evaluate the number of DNA double-strand breaks (DSBs) induced by in vitro targeted radionuclide therapy (TRT). This work represents the first step toward exploring underlying biologic mechanisms and the influence of physical and chemical parameters to enable a better response prediction in patients. We used this tool to characterize early DSB induction by 177Lu-DOTATATE, a commonly used TRT for neuroendocrine tumors. Methods: A multiscale approach was implemented to simulate the number of DSBs produced over 4 h by the cumulated decays of 177Lu distributed according to the somatostatin receptor binding. The approach involves 2 sequential simulations performed with Geant4/Geant4-DNA. The radioactive source is sampled according to uptake experiments on the distribution of activities within the medium and the planar cellular cluster, assuming instant and permanent internalization. A phase space is scored around the nucleus of the central cell. Then, the phase space is used to generate particles entering the nucleus containing a multiscale description of the DNA in order to score the number of DSBs per particle source. The final DSB computations are compared with experimental data, measured by immunofluorescent detection of p53-binding protein 1 foci. Results: The probability of electrons reaching the nucleus was significantly influenced by the shape of the cell compartment, causing a large variance in the induction pattern of DSBs. A significant difference was found in the DSBs induced by activity distributions in cell and medium, as is explained by the specific energy ([Formula: see text]) distributions. The average number of simulated DSBs was 14 DSBs per cell (range, 7-24 DSBs per cell), compared with 13 DSBs per cell (range, 2-30 DSBs per cell) experimentally determined. We found a linear correlation between the mean absorbed dose to the nucleus and the number of DSBs per cell: 0.014 DSBs per cell mGy-1 for internalization in the Golgi apparatus and 0.017 DSBs per cell mGy-1 for internalization in the cytoplasm. Conclusion: This simulation tool can lead to a more reliable absorbed-dose-to-DNA correlation and help in prediction of biologic response.
Keywords: 177Lu-DOTATATE; DNA double-strand break simulation; Geant4-DNA; dose–effect relationship; targeted radionuclide therapy.
© 2022 by the Society of Nuclear Medicine and Molecular Imaging.