ESTRO 2025 - Abstract Book

S2929

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

4256

Digital Poster Comparative analysis of Monte Carlo algorithms for low-energy photon dose calculation Sophia Galvez 1 , Jorge Jara 1 , Sebastián Martinez 1 , Maria Pía Valenzuela 1 , Ignacio Jara 1 , Andrea Russomando 1 , Rodrigo Cherubini 2 1 Physics, Pontifical Catholic University, Santiago, Chile. 2 Medical Physics, UC CHRISTUS, Santiago, Chile Purpose/Objective: This study aimed to evaluate the performance of the Monte Carlo (MC) codes PENELOPE and FLUKA in the low energy range for photon irradiations, with a focus on how the limitations of these codes in estimating energy deposition influence the prediction of radiation-induced effects. To address this, the spectra obtained were translated into cell survival curves through MC-based DNA damage estimation combined with a mechanistic model. The results were benchmarked against available experimental data on the V79 cell line. Material/Methods: A software chain was designed to validate the procedure. As a benchmark, data from Cobalt-60 irradiations were used. The geometry was reproduced in the Monte Carlo code, and the profile of secondary charged particles was extracted to estimate the effect on DNA damage. This step was necessary because MCDS does not allow direct work with photons [1][2]. The result was combined with a mechanistic model [3] that estimates cell survival, following a procedure already validated for protons [4]. The experimental setup [5] was reproduced in both FLUKA [6] and PENELOPE [7]. This approach allowed the comparison to be focused on the ultrasoft X-ray range, as the study reports results for characteristic K-line of titanium and aluminum, with average energies of 1.49 keV and 4.5 keV, respectively. The lower energy transport thresholds in each code were set at 1 and a few hundred eV, respectively. Results: The predictive chain performed well in the case of Cobalt-60 in figure 1a. The RMSE between the prediction and the experimental data was ~0.019 for PENELOPE and~0.017 for FLUKA. The results for ultrasoft photons are shown in figure 1b. In this case, the RMSE values are ~0.053 and ~0.089 for Ti and ~0.060 and ~0.179 for PENELOPE and FLUKA, respectively.

Conclusion: The results showed that at MeV energies, both codes performed well. However, at lower energies, significant differences in the spectra by PENELOPE and FLUKA affected DNA damage predictions and cell survival estimates. Although FLUKA has a lower photon transport energy threshold than the one used in the comparison experiment, in this energy range, the portion of the spectrum that is truncated has a significant impact on the final results.