Application of Geant4-DNA for simulating water radiolysis induced by Auger electron-emitting radionuclides.

Auger-emitting radionuclides have potential application in targeted radiotherapy, particularly for metastatic cancers. This possibility, especially, is stemmed from their characteristic short-range (a few μm) in biological systems allowing localization of high dose within small tumours. To explore this potential application, a Geant4 Monte Carlo toolkit has been employed to simulate the energy deposition of different radionuclides in a water model. The Geant4 Monte Carlo toolkit has model packages to simulate the interaction of radiation with matter and with diverse applications such as studies in science and medicine. In this study, the Geant4-DNA package was used to simulate the radiolytic yields induced by some Auger electron-emitting (AE) radionuclides including; I-131, I-125 and Pd-103, In-111, Ru-97 and Rh-103 m in water model. The results showed that the transient yield of the radiolytic species is characterized by the kinetic energies of the emitted electrons. It was observed that almost all the radionuclides, except I-131, deposited more energy in their proximity thereby inducing a high density of spurs to interact in a short time. It is, therefore, important to consider the kinetic energies of the emitted particles in choosing a radionuclide for specified targeted radiotherapy. This means that apart from their toxicity, compatibility with chelator and carrier molecules, and method of production, we can predict radionuclides such as In-111, Ru-97, Pb-103 m and I-125 could be relevant for targeted radiotherapy for the treatment of metastasis lesions, or tiny tumours at the cellular level, and tumours after surgical resection.