Monte Carlo Damage Simulation Code Research Articles

An inter-comparison between radiobiological characteristics of a commercial low-energy IORT system by Geant4-DNA and MCDS Monte Carlo codes

Introduction The need for accurate relative biological effectiveness (RBE) estimation for low energy therapeutic X-rays (corresponding to 50 kV nominal energy of a commercial low-energy IORT system (INTRABEAM)) is a crucial issue due to increased radiobiological effects, respect to high energy photons. Modeling of radiation-induced DNA damage through Monte Carlo (MC) simulation approaches can give useful information. Hence, this study aimed to evaluate and compare RBE of low energy therapeutic X-rays using Geant4-DNA toolkit and Monte Carlo damage simulation (MCDS) code. Materials and methods RBE calculations were performed considering the emitted secondary electron spectra through interactions of low energy X-rays inside the medium. In Geant4-DNA, the DNA strand breaks were obtained by employing a B-DNA model in physical stage with 10.79 eV energy-threshold and the probability of hydroxyl radical’s chemical reactions of about 0.13%. Furthermore, RBE estimations by MCDS code were performed under fully aerobic conditions. Results Acquired results by two considered MC codes showed that the same trend is found for RBEDSB and RBESSB variations. Totally, a reasonable agreement between the calculated RBE values (both RBESSB and RBEDSB) existed between the two considered MC codes. The mean differences of 9.2% and 1.8% were obtained between the estimated RBESSB and RBEDSB values by two codes, respectively. Conclusion Based on the obtained results, it can be concluded that a tolerable accordance is found between the calculated RBEDSB values through MCDS and Geant4-DNA, a fact which appropriates both codes for RBE evaluations of low energy therapeutic X-rays, especially in the case of RBEDSB where lethal damages are regarded.

Monte Carlo simulations of cell survival in proton SOBP.

Objective. The objective of this study is to develop a multi-scale modeling approach that accurately predicts radiation-induced DNA damage and survival fraction in specific cell lines.Approach. A Monte Carlo based simulation framework was employed to make the predictions. The FLUKA Monte Carlo code was utilized to estimate absorbed doses and fluence energy spectra, which were then used in the Monte Carlo Damage Simulation code to compute DNA damage yields in Chinese hamster V79 cell lines. The outputs were converted into cell survival fractions using a previously published theoretical model. To reduce the uncertainties of the predictions, new values for the parameters of the theoretical model were computed, expanding the database of experimental points considered in the previous estimation. Simulated results were validated against experimental data, confirming the applicability of the framework for proton beams up to 230 MeV. Additionally, the impact of secondary particles on cell survival was estimated.Main results. The simulated survival fraction versus depth in a glycerol phantom is reported for eighteen different configurations. Two proton spread out Bragg peaks at several doses were simulated and compared with experimental data. In all cases, the simulations follow the experimental trends, demonstrating the accuracy of the predictions up to 230 MeV.Significance. This study holds significant importance as it contributes to the advancement of models for predicting biological responses to radiation, ultimately contributing to more effective cancer treatment in proton therapy.

Incorporating oxygenation levels in analytical DNA-damage models—quantifying the oxygen fixation mechanism

Purpose. To develop a framework to include oxygenation effects in radiation therapy treatment planning which is valid for all modalities, energy spectra and oxygen levels. The framework is based on predicting the difference in DNA-damage resulting from ionising radiation at variable oxygenation levels. Methods. Oxygen fixation is treated as a statistical process in a simplified model of complex and simple damage. We show that a linear transformation of the microscopic oxygen fixation process allows to extend this to all energies and modalities, resulting in a relatively simple rational polynomial expression. The model is expanded such that it can be applied for polyenergetic beams. The methodology is validated using Microdosimetric Monte Carlo Damage Simulation code (MCDS). This serves as a bootstrap to determine relevant parameters in the analytical expression, as MCDS is shown to be extensively verified with published empirical data. Double-strand break induction as calculated by this methodology is compared to published proton experiments. Finally, an example is worked out where the oxygen enhancement ratio (OER) is calculated at different positions in a clinically relevant spread out Bragg peak (SOBP) dose deposition in water. This dose deposition is obtained using a general Monte Carlo code (FLUKA) to determine dose deposition and locate fluence spectra. Results. For all modalities (electrons, protons), the damage categorised as complex could be parameterised to within 0.3% of the value calculated using microdosimetric Monte Carlo. The proton beam implementation showed some variation in OERs which differed slightly depending on where the assessment was made; before the SOBP, mid-SOBP or at the distal edge. Environment oxygenation was seen to be the more important variable. Conclusions. An analytic expression calculating complex damage depending on modality, energy spectrum, and oxygenation levels was shown to be effective and can be readily incorporated in treatment planning software, to take into account the impact of variable oxygenation, forming a first step to an optimised treatment based on biological factors.

SU-E-T-495: Monte Carlo Simulations of Relative DNA Damage From KV CBCT Radiation

Purpose: Daily imaging protocols using kilovoltage cone beam CT (kV CBCT) have the potential to accumulate non‐trivial doses (up to several percent of the prescription dose) to the imaged volume which could have implications for planning decisions or the induction of secondary cancers. When CBCT dose is added to therapeutic dose, it may be necessary to account for differences in the relative biological effectiveness (RBE). We conducted a Monte Carlo study to investigate the relative number and complexity of DNA double strand breaks (DSBs) that Result from kV CBCT radiation compared to Co‐60 as a reference for general external beam radiation. Methods: A method was developed for coupling the radiation transport code (PENELOPE) with a Monte Carlo Damage Simulation (MCDS) code that predicts relative numbers and complexity of DSBs. The PENELOPE simulations generated electron spectra relevant for the MCDS input consisting of (i) electrons generated outside of a cell nucleus that drift in and (ii) electrons created within the nuclear volume, both without the continued slowing within the nucleus itself that is simulated implicitly by the MCDS code. Various configurations were considered (surface/depth, bowtie filter thickness, kV energy, and degrees of oxygenation). Results: The RBE for DSB induction in the kV CBCT sources ranged from 1.14 to 1.19 with increased complexity compared to that of Co‐60 for the majority of conditions; however, values as high as 1.45 were calculated in extreme circumstances. The RBE increased for anoxic conditions, at the phantom surface, for lower energies and for less filtration. Conclusions:Our results suggest kV CBCT sources produce more DNA damage than therapeutic radiation for a given absorbed dose and the relative difference can depend on several factors. This has potential implications for calculating the probability for inducing secondary cancers through the use of image guidance radiation.

Monte Carlo simulations of therapeutic proton beams for relative biological effectiveness of double-strand break

Purpose: The relative biological effectiveness (RBE) values relative to 60Co for the induction of double-strand breaks (DSB) were calculated for therapeutic proton beams. RBE-weighted absorbed doses were determined at different depths in a water phantom for proton beams.Materials and methods: The depth-dose distributions and the fluence spectra for primary protons and secondary particles were calculated using the FLUKA (FLUktuierende KAskade) MC (Monte Carlo) transport code. These spectra were combined with the MCDS (Monte Carlo damage simulation) code to simulate the spectrum-averaged yields of clustered DNA lesions. RBE for the induction of DSB were then determined at different depths in a water phantom for the unmodulated and modulated proton beams.Results: The maximum RBE for the induction of DSB at 1 Gy absorbed dose was found about 1.5 at 0.5 cm distal to the Bragg peak maximum for an unmodulated 160 MeV proton beam. The RBE-weighted absorbed dose extended the biologically effective range of the proton beam by 1.9 mm. The corresponding maximum RBE value was inversely proportional to the proton beam energy, reaching a value of about 1.9 for 70 MeV proton beam. For a modulated 160 MeV proton beam, the RBE weightings were more pronounced near the spread-out Bragg peak (SOBP) distal edge.Conclusions: It was demonstrated that a fast MCDS code could be used to simulate the DNA damage yield for therapeutic proton beams. Simulated RBE for the induction of DSB were comparable to RBE measured in vitro and in vivo. Depth dependent RBE values in the SOBP region might have to be considered in certain treatment situations.