2970 - Estimation of HSGc-C5 Cell Survival After multi-Ion Irradiation Using Geant4-DNA Monte Carlo Simulation

Materials/Methods: The Geant4-DNA MCTS framework was used to estimate the survival fraction (SF) of HSGc-C5 cells, based on the “molecularDNA” example. The cell nucleus was modeled as an ellipsoid with dimensions of 13.9 µm × 3.7 µm × 13.9 µm (volume of 374 µm³). A total of 6.4 Gbp of DNA was packed into the modeled cell using a fractal-based structure with modifications to the default DNA unit geometry. In the Geant4-DNA simulations, G4EmDNAPhysics_option4 and G4EmDNAChemistry_option2 were used as the physics and chemistry constructors, respectively, while other DNA damage scoring parameters were kept at default settings. To compare predicted SF with published experimental data [1], beam energies for helium-, carbon-, oxygen-, and neon-ion beams were determined by matching reported linear energy transfer (LET) values, using ICRU 90 data to derive the corresponding ion energies for simulation. The resulting DNA damage yields were used as inputs to the TLK model; experimental-condition parameters were set according to the reference [1], and lethality-related TLK parameters were optimized to fit the measured SF data.

Results: Beam energies for helium-, carbon-, oxygen-, and neon-ion beams were derived to match the LET values reported in the reference and were simulated in Geant4-DNA. Six TLK model parameters (?₁, ?₂, ?, ß₁, ß₂, and ?) were optimized for each ion species by fitting to measured SF data; ß₁ was fixed at 0. The optimized TLK parameters are summarized in Table 1. The predicted SF curves showed reasonable agreement with the experimental data points. However, for helium and carbon, one data interval exhibited an increase in SF despite increasing LET (He: 3.5–4.5 keV/µm; C: 48.8–59.1 keV/µm), which may be attributable to stochastic, track-structure–driven spatial heterogeneity in strand-break (SB) deposition in regions of small LET differences and to simplifications in the complex-damage calculation approach

Conclusion: Using the Geant4-DNA MCTS code in conjunction with the TLK model, cell survival following multi-ion irradiation was successfully predicted.