GATE Monte Carlo evaluation of cellular dosimetry for ¹¹⁹Sb in targeted radionuclide therapy

This study evaluates the cellular dosimetry of Antimony-119 (¹¹⁹Sb) as a candidate for targeted radionuclide therapy (TRT), using Monte Carlo simulations with the GATE toolkit. The goal is to assess the microdosimetric characteristics of ¹¹⁹Sb as an Auger and Internal conversion electron emitter and compare its performance with other clinically relevant radionuclides-¹⁷⁷Lu, ¹²⁵I, ¹²³I, and ¹⁰³Pd-across different cellular geometries and emission spectra.

Monte Carlo simulations were performed using the GATE toolkit to model energy deposition at the cellular level. Two cell geometries were considered: one with a centrally located nucleus and another with the nucleus adjacent to the cell membrane, reflecting real biological diversity. S-values (absorbed dose per decay) were calculated for three possible locations of radioactivity (nucleus, cytoplasm, and cell membrane). Three emission spectra and two physics models were used to ensure robust results. Simulations were benchmarked against established dosimetry models (MIRDcell, PENELOPE, and Geant4).

¹¹⁹Sb delivered the highest and most localized dose to the cell nucleus, particularly when radioactivity was at the cell membrane, outperforming the other radionuclides tested. Its S-values were up to five times higher than ¹⁷⁷Lu and four times higher than ¹²⁵I in certain configurations. This effect remained strong even when the nucleus was off-center, suggesting ¹¹⁹Sb's effectiveness is independent to nucleus locations diversities. Auger and Coster-Kronig electrons dominated the energy deposition for most isotopes in single cell configurations, while internal conversion electrons contributed significantly for ¹¹⁹Sb in the cytoplasmic and membrane configurations.

¹¹⁹Sb is a promising candidate for TRT of micrometastases and single cancer cells due to its high and stable S-values, especially when radioactivity is localized at the cell membrane. Its dosimetric stability across nucleus positions makes it particularly suitable for therapeutic applications where cellular morphology varies. However, production and radiolabeling challenges may limit its clinical adoption.