Fast Monte Carlo simulation of DNA damage induction by Auger-electron emission

Purpose: A local damage model (LDM) was developed to estimate the biological efficiency of Auger-electron-emitting radionuclides. Materials and methods: The LDM required information on the local dose distribution, local energy spectrum, and clustered DNA damage yields in the cell nucleus. To apply the model, the nucleus was divided into concentric shells where each shell contributed its own local dose, energy spectrum, and damage yield. The local doses and energy spectra were computed using the PENELOPE (PENetration and Energy LOss of Positrons and Electrons) code. The DNA damage yields were estimated using the MCDS (Monte Carlo damage simulation) code. Results: For a typical 4-μm radius mammalian cell nucleus, the absorbed doses to the cell nucleus per unit cumulated activity, equal to 0.0065, 0.00418, 0.0028, 0.0027 and 0.0015 Gy Bq^-1 s^-1 for ¹²⁵I, ¹¹⁹Sb, ¹²³I, ¹¹¹In and ^99mTc, were within 6% difference with the MIRD (Medical Internal Radiation Dose) published data. The simulated total (simple and complex) single-strand break (SSB) and double-strand break (DSB) yields were in the same order, i.e., ¹²⁵I > ¹¹⁹Sb > ¹²³I > ¹¹¹In > ^99mTc. The agreement between present results and literature data for the DNA damage yields was generally good. More than 75% of the total SSB and DSB yields were contributed from regions within 2.5 μm of the nucleus center. Conclusions: The proposed methodology was computationally efficient and could be applied to other irradiation geometries such as cell clusters.