Limitations (and merits) of PENELOPE as a track-structure code

Facultat de Física (ECM and ICC), Universitat de Barcelona, Barcelona, Spain.
International Journal of Radiation Biology (Impact Factor: 1.69). 08/2011; 88(1-2):66-70. DOI: 10.3109/09553002.2011.598209
Source: PubMed


To outline the limitations of PENELOPE (acronym of PENetration and Energy LOss of Positrons and Electrons) as a track-structure code, and to comment on modifications that enable its fruitful use in certain microdosimetry and nanodosimetry applications.
Attention is paid to the way in which inelastic collisions of electrons are modelled and to the ensuing implications for microdosimetry analysis.
Inelastic mean free paths and collision stopping powers calculated with PENELOPE and two well-known optical-data models are compared. An ad hoc modification of PENELOPE is summarized where ionization and excitation of liquid water by electron impact is simulated using tables of realistic differential and total cross sections.
PENELOPE can be employed advantageously in some track-structure applications provided that the default model for inelastic interactions of electrons is replaced by suitable tables of differential and total cross sections.

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Available from: Mariel Elisa Galassi, Jun 08, 2015
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    • "For this step, we used the most accurate physics model available for gold element, 'Geant4- Penelope', which tracks electrons down to an energy of 250 eV. This model has shown to be an accurate low-energy model for nanodosimetry and agrees well with event-by-event track structure codes (Bernal and Liendo 2009, Fernández-Varea et al 2012, Champion 2014). To obtain the DEF, the simulations were repeated replacing the GNPs with water nanoparticles (WNPs) with the same size, and the same Geant4-Penelope physics with the same energy cut-off of 250 eV. "
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    ABSTRACT: Gold nanoparticles (GNPs) have shown potential to be used as a radiosensitizer for radiation therapy. Despite extensive research activity to study GNP radiosensitization using photon beams, only a few studies have been carried out using proton beams. In this work Monte Carlo simulations were used to assess the dose enhancement of GNPs for proton therapy. The enhancement effect was compared between a clinical proton spectrum, a clinical 6 MV photon spectrum, and a kilovoltage photon source similar to those used in many radiobiology lab settings. We showed that the mechanism by which GNPs can lead to dose enhancements in radiation therapy differs when comparing photon and proton radiation. The GNP dose enhancement using protons can be up to 14 and is independent of proton energy, while the dose enhancement is highly dependent on the photon energy used. For the same amount of energy absorbed in the GNP, interactions with protons, kVp photons and MV photons produce similar doses within several nanometers of the GNP surface, and differences are below 15% for the first 10 nm. However, secondary electrons produced by kilovoltage photons have the longest range in water as compared to protons and MV photons, e.g. they cause a dose enhancement 20 times higher than the one caused by protons 10 μm away from the GNP surface. We conclude that GNPs have the potential to enhance radiation therapy depending on the type of radiation source. Proton therapy can be enhanced significantly only if the GNPs are in close proximity to the biological target.
    Physics in Medicine and Biology 11/2014; 59(24):7675-7689. DOI:10.1088/0031-9155/59/24/7675 · 2.76 Impact Factor
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    • "For each simulated photoelectric absorption within a AuNP, the escaping electron and photon tracks were followed in 3D and the local nanoscale energy deposition was recorded using a customized tally. Although PENELOPE has limitations with regards to very low-energy electron inelastic scattering simulation and track structure calculations (Bernal and Liendo 2009, Nikjoo et al 2006), we chose this code due to its comprehensive coupled electron/photon transport simulation through various mediums including tissue and gold, and flexibility of its geometry package (Fernandez-Varea et al 2012). Furthermore, PENELOPE offers a highly customizable code allowing for user defined tallies that were required for this study (Salvat et al 2008). "
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    ABSTRACT: Radiosensitization using gold nanoparticles (AuNPs) has been shown to vary widely with cell line, irradiation energy, AuNP size, concentration and intracellular localization. We developed a Monte Carlo-based AuNP radiosensitization predictive model (ARP), which takes into account the detailed energy deposition at the nano-scale. This model was compared to experimental cell survival and macroscopic dose enhancement predictions. PC-3 prostate cancer cell survival was characterized after irradiation using a 300 kVp photon source with and without AuNPs present in the cell culture media. Detailed Monte Carlo simulations were conducted, producing individual tracks of photoelectric products escaping AuNPs and energy deposition was scored in nano-scale voxels in a model cell nucleus. Cell survival in our predictive model was calculated by integrating the radiation induced lethal event density over the nucleus volume. Experimental AuNP radiosensitization was observed with a sensitizer enhancement ratio (SER) of 1.21 ± 0.13. SERs estimated using the ARP model and the macroscopic enhancement model were 1.20 ± 0.12 and 1.07 ± 0.10 respectively. In the hypothetical case of AuNPs localized within the nucleus, the ARP model predicted a SER of 1.29 ± 0.13, demonstrating the influence of AuNP intracellular localization on radiosensitization.
    Physics in Medicine and Biology 04/2013; 58(10):3075-3087. DOI:10.1088/0031-9155/58/10/3075 · 2.76 Impact Factor
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    ABSTRACT: The assessment of radiotoxicity for heterogeneously distributed tritium should be based on the subcellular dose and relative biological effectiveness (RBE) for cell nucleus. In the present work, geometry-dependent absorbed dose and RBE were calculated using Monte Carlo codes for tritium in the cell, cell surface, cytoplasm, or cell nucleus. Penelope (PENetration and Energy LOss of Positrins and Electrons) code was used to calculate the geometry-dependent absorbed dose, lineal energy, and electron fluence spectrum. RBE for the intestinal crypt regeneration was calculated using a lineal energy-dependent biological weighting function. RBE for the induction of DNA double strand breaks was estimated using a nucleotide-level map for clustered DNA lesions of the Monte Carlo damage simulation (MCDS) code. For a typical cell of 10 μm radius and 5 μm nuclear radius, tritium in the cell nucleus resulted in much higher RBE-weighted absorbed dose than tritium distributed uniformly. Conversely, tritium distributed on the cell surface led to trivial RBE-weighted absorbed dose due to irradiation geometry and great attenuation of beta particles in the cytoplasm. For tritium uniformly distributed in the cell, the RBE-weighted absorbed dose was larger compared to tritium uniformly distributed in the tissue. Cellular- and micro-dosimetry models were developed for the assessment of heterogeneously distributed tritium.
    International Journal of Radiation Biology 07/2011; 88(1-2):151-7. DOI:10.3109/09553002.2011.595876 · 1.69 Impact Factor
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