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Purpose: In this study, the effect of 111 In position and Auger electron energy on direct induction of DSBs was investigated., Materials and Methods: The Geant4-DNA simulation toolkit was applied using a simple B-DNA form extracted from PDBlib library. First, the simulation was performed for electrons with energies of 111 In and equal emission probabilities to find the most effective electron energies. Then, 111 In Auger electrons' actual spectrum was considered and their contribution in DSB induction analysed., Results: The results showed that the most effective electron energy is 183 eV, but due to the higher emission probability of 350 eV electrons, most of the DSBs were induced by the latter electrons. Also, it was observed that most of the DSBs are induced by electrons emitted within 4 nm of the central axis of the DNA and were mainly due to breaks with <4 base pairs distance in opposing strands. Whilst, when 111 In atoms are very close to the DNA, 1.3 DSBs have been obtained per decay of 111 In atoms., Conclusions: The results show that the most effective Auger electrons are the 350 eV electrons from 111 In atoms with <4 nm distance from the central axis of the DNA which induce ∼1.3 DSBs per decay when bound to the DNA. This value seems reasonable when compared with the reported experimental data.

TOPAS-nBio was used to simulate, collision-to-collision, the complete trajectories of electrons in water generated during the explicit simulation of 64Cu decay. S-values and direct damage to the DNA were calculated representing the cell (C) and the cell nucleus (N) with concentric spheres of 5 μm and 4 μm in radius, respectively. The considered 'target'←'source' configurations, including the cell surface (Cs) and cytoplasm (Cy), were: C←C, C←Cs, N←N, N←Cy and N←Cs. Ionization cluster size distributions were also calculated in a cylinder immersed in water corresponding to a DNA segment of 10 base-pairs in length (diameter 2.3 nm, length 3.4 nm), modeling a radioactive point source moving from the central axis to the edge of the cylinder. For that, the first moment (M1) and cumulative probability of having a cluster size of 2 or more ionizations in the cylindrical volume (F2) were obtained. Finally, the direct damage to the DNA was estimated by quantifying double-strand breaks (DSBs) using the clustering algorithm DBSCAN. The S-values obtained with TOPAS-nBio for 64Cu were 7.879 × 10-4 ± 5 × 10-7, 4.351 × 10-4 ± 6 × 10-7, 1.442 × 10-3 ± 1 × 10-6, 2.596 × 10-4 ± 8 × 10-7, 1.127 × 10-4 ± 4 × 10-7 Gy Bq-s-1 for the configurations C←C, C←Cs, N←N, N←Cy and N←Cs, respectively. The difference of these values, compared with previously reported S-values for 64Cu with the code MNCP and software MIRDCell, ranged from -4% to -25% for the configurations N←N and N←Cs, respectively. On the other hand, F2 was maximum with the source at the center of the cylinder 0.373 ± 0.001, and monotonically decreased until reaching a value of 0.058 ± 0.001 at 2.3 nm. The same behavior was observed for M1 with values ranging from 2.188 ± 0.004 to 0.242 ± 0.002. Finally, the DBSCAN algorithm showed that the mean number of DNA DSBs per decay were 0.187 ± 0.001, 0.0317 ± 0.0005, and 0.0125 ± 0.0002 DSB-(Bq-s)-1 for the configurations N←N, N←Cs, and N←Cy, respectively. In conclusion, the results of the S-values show that the absorbed dose strongly depends on the distribution of the radionuclide in the cell, the dose being higher when 64Cu is internalized in the cell nucleus, which is reinforced by the nanodosimetric study by the presence of DNA DSBs attributable to the Auger electrons emitted during the decay of 64Cu.

Purpose: For the past two decades, high‐Z nanoparticles have been of high interest to improve the therapeutic outcomes of radiation therapy, especially for low‐energy x‐rays. Monte Carlo (MC) simulations have been used to evaluate the boost of dose deposition induced by Auger electrons near the nanoparticle surface, by calculating average energy deposition at the nanoscale. In this study, we propose to go beyond average quantities and quantify the stochastic nature of energy deposition at such a scale. We present results of probability density of the specific energy (restricted to ionization, excitation and electron attachment events) in cylindrical nanotargets of height and radius set at 10 nm. This quantity was evaluated for nanotargets located within 200 nm around 5–50 nm gold nanoparticles (GNPs), for 20–90 keV photon irradiation. Methods: This nanodosimetry study was based on the MC simulation MDM that allows tracking of electrons down to thermalization energy. We introduced a new quantity, namely the probability enhancement ratio (PER), by estimating the probability of imparting to nanotargets a restricted specific energy larger than a threshold z0 (1, 10, and 20 kGy), normalized to the probability for pure water. The PER was calculated as a function of the distance between the nanotarget and the GNP surface. The threshold values were chosen in light of the biophysical model NanOx that predicts cell survival by calculating local lethal events based on the restricted specific energy and an effective local lethal function. z0 then represents a threshold above which the nanotarget damages induce efficiently cell death. Results: Our calculations showed that the PER varied a lot with the GNP radius, the photon energy, z0 and the distance of the GNP to the nanotarget. The highest PER was 95 when the nanotarget was located at 5 nm from the GNP surface, for a photon energy of 20 keV, a threshold of 20 kGy, and a GNP radius of 50 nm. This enhancement dramatically decreased with increasing GNP‐nanotarget distances as it went below 1.5 for distances larger than 200 nm. Conclusions: The PER seems better adapted than the mean dose deposition to describe the formation of biological damages. The significant increase of the PER within 200 nm around the GNP suggests that severe damages could occur for biological nanotargets located near the GNP. These calculations will be used as an input of the biophysical model NanOx to convert PER into estimation of radiation‐induced cell death enhanced by GNPs. [ABSTRACT FROM AUTHOR]

Purpose: Small‐scale dosimetry studies generally consider an artificial environment where the tumors are spherical and the radionuclides are homogeneously biodistributed. However, tumor shapes are irregular and radiopharmaceutical biodistributions are heterogeneous, impacting the energy deposition in targeted radionuclide therapy. To bring realism, we developed a dosimetric methodology based on a three‐dimensional in vitro model of follicular lymphoma incubated with rituximab, an anti‐CD20 monoclonal antibody used in the treatment of non‐Hodgkin lymphomas, which might be combined with a radionuclide. The effects of the realistic geometry and biodistribution on the absorbed dose were highlighted by comparison with literature data. Additionally, to illustrate the possibilities of this methodology, the effect of different radionuclides on the absorbed dose distribution delivered to the in vitro tumor were compared. Methods: The starting point was a model named multicellular aggregates of lymphoma cells (MALC). Three MALCs of different dimensions and their rituximab biodistribution were considered. Geometry, antibody location and concentration were extracted from selective plane illumination microscopy. Assuming antibody radiolabeling with Auger electron (125I and 111In) and β− particle emitters (177Lu, 131I and 90Y), we simulated energy deposition in MALCs using two Monte Carlo codes: Geant4‐DNA with "CPA100" physics models for Auger electron emitters and Geant4 with "Livermore" physics models for β− particle emitters. Results: MALCs had ellipsoid‐like shapes with major radii, r, of ~0.25, ~0.5 and ~1.3 mm. Rituximab was concentrated in the periphery of the MALCs. The absorbed doses delivered by 177Lu, 131I and 90Y in MALCs were compared with literature data for spheres with two types of homogeneous biodistributions (on the surface or throughout the volume). Compared to the MALCs, the mean absorbed doses delivered in spheres with surface biodistributions were between 18% and 38% lower, while with volume biodistribution they were between 15% and 29% higher. Regarding the radionuclides comparison, the relationship between MALC dimensions, rituximab biodistribution and energy released per decay impacted the absorbed doses. Despite releasing less energy, 125I delivered a greater absorbed dose per decay than 111In in the r ~ 0.25 mm MALC (6.78·10−2 vs 6.26·10−2 µGy·Bq−1·s−1). Similarly, the absorbed doses per decay in the r ~ 0.5 mm MALC for 177Lu (2.41·10−2 µGy·Bq−1·s−1) and 131I (2.46·10−2 µGy·Bq−1·s−1) are higher than for 90Y (1.98·10−2 µGy·Bq−1·s−1). Furthermore, radionuclides releasing more energy per decay delivered absorbed dose more uniformly through the MALCs. Finally, when considering the radiopharmaceutical effective half‐life, due to the biological half‐life of rituximab being best matched by the physical half‐life of 177Lu and 131I compared to 90Y, the first two radionuclides delivered higher absorbed doses. Conclusion: In the simulated configurations, β− emitters delivered higher and more uniform absorbed dose than Auger electron emitters. When considering radiopharmaceutical half‐lives, 177Lu and 131I delivered absorbed doses higher than 90Y. In view of real irradiation of MALCs, such a work may be useful to select suited radionuclides and to help explain the biological effects. [ABSTRACT FROM AUTHOR]

A Monte Carlo simulation of production and emission of Auger electron signals in Auger electron spectroscopy (AES) has been performed to calculate the dependence of Auger electron intensity on film thickness for a film/substrate specimen. The electron spectrum is simulated, covering the energy range from the elastic peak down to Auger electron peak, by including bulk loss peak of electronic excitation. This simulation is based on the use of Mott’s cross section for electron elastic scattering and Penn’s dielectric function approach to electron inelastic scattering. Bulk plasmon excitation peaks contributed from both film and substrate are found in the low loss region near the elastic peak and the AES signal peak. The background subtraction was then performed for the simulated Auger electron spectrum, leading to obtain the approximate exponential decay behavior of Auger signal intensity varied with the film thickness. It is found that single value of effective attenuation length (EAL) is not enough for an accurate measurement of film thickness. We define two attenuation parameters to characterize the decay functional shape used as the calibration curve for accurate film thickness determination if the universal expression on experimental condition will be found. [ABSTRACT FROM AUTHOR]

This work presents the simulation of monoenergetic electron slowing-down spectra in liquid water by the Geant4-DNA extension of the Geant4 Monte Carlo toolkit (release 10.2p01). These spectra are simulated for several incident energies using the most recent Geant4-DNA physics models, and they are compared to literature data. The influence of Auger electron production is discussed. For the first time, a dedicated Geant4-DNA example allowing such simulations is described and is provided to Geant4 users, allowing further verification of Geant4-DNA track structure simulation capabilities. [ABSTRACT FROM AUTHOR]

Purpose:To simulate the deceleration processes of secondary electrons produced by a high-energy Auger electron in water, and particularly to focus on the spatial and temporal distributions of the secondary electron and the collision events (e.g. ionization, electronic excitation, and dissociative electron attachment) that are involved in the multiplication of lesions at sites of DNA damage. Materials and methods:We developed a dynamic Monte Carlo code that considers the Coulombic force between an ejected electron and its parent cation produced by the Auger electron in water. Thus our code can simulate some return electrons to the parent cations. Using the code, we calculated to within the order of femtoseconds the temporal evolution of collision events, the mean energy, and the mean traveling distance (including its spatial probability distribution) of the electron at an ejected energy of 20 eV. Results:Some of the decelerating electrons in water in the Coulombic field were attracted to the ionized atoms (cations) by the Coulombic force within hundreds of femtoseconds, although the force did not significantly enhance the number of ionization, electronic excitation, and dissociative electron attachment collision events leading to water radiolysis. Conclusions:The secondary electrons are decelerated in water by the Coulombic force and recombined to the ionized atoms (cations). Furthermore, the some return electrons might be prehydrated in water layer near the parent cation in DNA if the electrons might be emitted from the DNA. The prehydrated electron originated from the return electron might play a significant role in inducing DNA damage. [ABSTRACT FROM PUBLISHER]

To benchmark a Monte Carlo model of the Auger cascade that has been developed at the Australian National University (ANU) against the literature data. The model is applicable to any Auger-electron emitting radionuclide with nuclear structure data in the format of the Evaluated Nuclear Structure Data File (ENSDF). Schönfeld's algorithms and the BrIcc code were incorporated to obtain initial vacancy distributions due to electron capture (EC) and internal conversion (IC), respectively. Atomic transition probabilities were adopted from the Evaluated Atomic Data Library (EADL) for elements with atomic number, Z = 1–100. Atomic transition energies were evaluated using a relativistic Dirac-Fock method. An energy-restriction protocol was implemented to eliminate energetically forbidden transitions from the simulations. Calculated initial vacancy distributions and average energy spectra of 123I, 124I, and 125I were compared with the literature data. In addition, simulated kinetic energy spectra and frequency distributions of the number of emitted electrons and photons of the three iodine radionuclides are presented. Some examples of radiation spectra of individual decays are also given. Good agreement with the published data was achieved except for the outer-shell Auger and Coster-Kronig transitions. Nevertheless, the model needs to be compared with experimental data in a future study. [ABSTRACT FROM AUTHOR]

Purpose: To understand the biological effect of external and internal exposure from 137Cs, DNA damage spectrum induced by directly emitted electrons (γ-rays, internal conversion electrons, Auger electrons) from 137Cs was compared with that induced by 137Cs γ-rays. Methods: Monte Carlo track simulation method was used to calculate the microscopic energy deposition pattern in liquid water. Simulation was performed for the two simple target systems in microscale. Radiation sources were placed inside for one system and outside for another system. To simulate the energy deposition by directly emitted electrons from 137Cs placed inside the system, the multiple ejections of electrons after internal conversion were considered. In the target systems, induction process of DNA damage was modeled and simulated for both direct energy deposition and the water radical reaction on the DNA. The yield and spatial distribution of simple and complex DNA damage including strand breaks and base lesions were calculated for irradiation by electrons and γ-rays from 137Cs. Results: The simulation showed that the significant difference in DNA damage spectrum was not caused by directly ejected electrons and γ-rays from 137Cs. Conclusions: The result supports the existing perception that the biological effects by internal and external exposure by 137Cs are equivalent. [ABSTRACT FROM AUTHOR]

A revised atomic deexcitation framework for the Geant4 general purpose Monte Carlo toolkit capable of simulating full Auger deexcitation cascades was implemented in June 2015 release (version 10.2 Beta). An overview of this refined framework and testing of its capabilities is presented for the irradiation of gold nanoparticles (NP) with keV photon and MeV proton beams. The resultant energy spectra of secondary particles created within and that escape the NP are analyzed and discussed. It is anticipated that this new functionality will improve and increase the use of Geant4 in the medical physics, radiobiology, nanomedicine research and other low energy physics fields. [ABSTRACT FROM AUTHOR]

In this work was proposed a new radiotherapy enhancement method consisting of the administration of magnetic nanoparticles into the cells with further irradiation with a gamma-ray beam. As a result, adjusting the energy distribution of a gamma-ray beam and Fe abundance it is possible to achieve an extremely intensive electron emission because of a nuclear resonance. The produced conversion and Auger electrons can be used as an effective tool for DNA lesions production. We developed a Monte Carlo model for an electron and gamma emission by Fe nucleus using the Geant4 program package. The parameters of a resonant absorption were taken from Mössbauer spectra of magnetite nanoparticles synthesized for the administration into live cells. The space distribution of the radiation dose showed an increase in the dose of 2-2.5 times in the case of the natural abundance and more than 50 times in the case of the 66 % enrichment of the nanoparticles. [ABSTRACT FROM AUTHOR]

We present SIMION 8.1 Monte Carlo type simulations of the response function and detection solid angle for long lived Auger states (lifetime τ ~ 10-9 - 10-5 s) recorded by a hemispherical spectrograph with injection lens and position sensitive detector used for high resolution Auger spectroscopy of ion beams. Also included in these simulations for the first time are kinematic effects particular to Auger emission from fast moving projectile ions such as line broadening and solid angle limitations allowing for a more accurate and realistic line shape modeling. Our results are found to be in excellent agreement with measured electron line shapes of both long lived 1s2s2p 4P and prompt Auger projectile states formed by electron capture in collisions of 25.3 MeV F7+ with H2 and 12.0 MeV C4+ with Ne recorded at 0° to the beam direction. These results are important for the accurate evaluation of the 1s2s2p 4P/²P ratio of K-Auger cross sections whose observed non-statistical production by electron capture into He-like ions, recently a field of interesting interpretations, awaits further resolution. [ABSTRACT FROM AUTHOR]

Purpose: In this work the number of DNA single-strand breaks (SSB) and double-strand breaks (DSB) due to direct and indirect effects of Auger electrons from incorporated 123I and 125I have been calculated by using the Geant4-DNA toolkit. We have performed and compared the calculations for several cases: 125I versus 123I, source positions and direct versus indirect breaks to study the capability of the Geant4-DNA in calculations of DNA damage yields. Materials and methods: Two different simple geometries of a 41 base pair of B-DNA have been simulated. The location of 123I has been considered to be in 123IdUrd and three different locations for 125I. Results: The results showed that the simpler geometry is sufficient for direct break calculations while indirect damage yield is more sensitive to the helical shape of DNA. For 123I Auger electrons, the average number of DSB due to the direct hits is almost twice the DSB due to the indirect hits. Furthermore, a comparison between the average number of SSB or DSB caused by Auger electrons of 125I and 123I in 125IdUrd and 123IdUrd shows that 125I is 1.5 times more effective than 123I per decay. Conclusions: The results are in reasonable agreement with previous experimental and theoretical results which shows the applicability of the Geant-DNA toolkit in nanodosimetry calculations which benefits from the open-source accessibility with the advantage that the DNA models used in this work enable us to save the computational time. Also, the results showed that the simpler geometry is suitable for direct break calculations, while for the indirect damage yield, the more precise model is preferred. [ABSTRACT FROM AUTHOR]

Purpose: To further elucidate the mechanisms behind the strong biological effectiveness of DNA-incorporated Auger electron emitters 123I and 125I, which are mostly attributed to the shower of low-energy electrons released during the decay. A second, frequently mentioned cause can be seen in the charges accumulated during the Auger cascade on the decaying nuclide and its subsequent intra-molecular redistribution leading to a Coulomb explosion. Methods: To assess the size of the charge and the dimensions of DNA damage thus determined, the first Auger cascade was simulated by Monte Carlo methods. The consequences of intra-molecular charge transfer in terms of structural molecular alterations were estimated by density functional theory (DFT) calculations and folding with the results of the Monte Carlo studies. Results: Charge distributions of 123I and 125I were found to be very similar with values between + 1 and + 15 and a mean value of + 6.4. The molecules could tolerate charges up to + 5 (base), + 2 (nucleoside) and + 7 (nucleotide) without being destroyed. Conclusions: The strong molecular DNA damage after 123I and 125I decay depends very much on the size of the DNA molecule involved in the calculation. In general, not every decay can be expected to lead to a Coulomb explosion. [ABSTRACT FROM AUTHOR]

Purpose: To investigate differences in energy depositions and microdosimetric parameters of low-energy electrons in liquid and gaseous water using Monte Carlo track structure simulations. Materials and methods: KURBUC-liq (Kyushu University and Radiobiology Unit Code for liquid water) was used for simulating electron tracks in liquid water. The inelastic scattering cross sections of liquid water were obtained from the dielectric response model of Emfietzoglou et al. ( Radiation Research 2005;164:202-211). Frequencies of energy deposited in nanometre-size cylindrical targets per unit absorbed dose and associated lineal energies were calculated for 100-5000 eV monoenergetic electrons and the electron spectrum of carbon K edge X-rays. The results for liquid water were compared with those for water vapour. Results: Regardless of electron energy, there is a limit how much energy electron tracks can deposit in a target. Phase effects on the frequencies of energy depositions are largely visible for the targets with diameters and heights smaller than 30 nm. For the target of 2.3 nm by 2.3 nm (similar to dimension of DNA segments), the calculated frequency- and dose-mean lineal energies for liquid water are up to 40% smaller than those for water vapour. The corresponding difference is less than 12% for the targets with diameters ≥ 30 nm. Conclusions: Condensed-phase effects are non-negligible for microdosimetry of low-energy electrons for targets with sizes smaller than a few tens of nanometres, similar to dimensions of DNA molecular structures and nucleosomes. [ABSTRACT FROM AUTHOR]

Purpose: To calculate the absorbed fraction (AF) of low energy electrons in small tissue-equivalent spherical volumes by Monte Carlo (MC) track structure simulation and assess the influence of phase (liquid water versus density-scaled water vapor) and of the continuous-slowing-down approximation (CSDA) used in semi-analytic calculations. Methods: An event-by-event MC code simulating the transport of electrons in both the vapor and liquid phase of water using appropriate electron-water interaction cross sections was used to quantify the energy deposition of low-energy electrons in spherical volumes. Semi-analytic calculations within the CSDA using a convolution integral of the Howell range-energy expressions are also presented for comparison. Results: The AF for spherical volumes of radii from 10-1000 nm are presented for monoenergetic electrons over the energy range 100-10,000 eV and the two Auger-emitting radionuclides 125I and 123I. The MC calculated AF for the liquid phase are found to be smaller than those of the (density scaled) gas phase by up to 10-20% for the monoenergetic electrons and 10% for the two Auger-emitters. Differences between the liquid-phase MC results and the semi-analytic CSDA calculations are up to ∼ 55% for the monoenergetic electrons and up to ∼ 35% for the two Auger-emitters. Conclusions: Condensed-phase effects in the inelastic interaction of low-energy electrons with water have a noticeable but relatively small impact on the AF for the energy range and target sizes examined. Depending on the electron energies, the semi-analytic approach may lead to sizeable errors for target sizes with linear dimensions below 1 micron. [ABSTRACT FROM AUTHOR]

Abstract: The experiment with 125I-Auger electrons, interacting with gaseous nitrogen with size equivalent to segment of DNA in mass per unit area scale, are described. The discrete ionization cluster-size distributions have been obtained. The shapes of which are definitely determined by the size of the interaction volumes. The volume sizes studied in the present work are comparable with a segment of DNA and of nucleosome. The experiments have been carried out with the set up, called Jet Counter, and are the first cluster-size distributions as yet measured for an Auger-electron emitter like 125I. The experimental results have been compared with those obtained by Monte Carlo simulation. The results for 125I have been compared with calculated cluster size distribution for 131I. [Copyright &y& Elsevier]

Abstract: Evaluation of the intracellular distribution of radionuclides used for targeted radiotherapy (tRT) is essential for accurate dosimetry. Therefore, a direct and quantitative method for subcellular micro-autoradiography using radiation sensitive polymers (PMMA, UV1116 and AZ40XT) was developed. The electron exposure dose in radio-labelled cells due to Auger and internal conversion (IC) electron emissions of indium (111In), a radionuclide currently used for tRT, was calculated using Monte Carlo (MC) simulation. Electron beam lithography using pre-defined exposure doses was used to calibrate the resist response. The topography of the exposed and developed resists was analysed with atomic force microscopy (AFM) and the resulting pattern depth was related to a specific exposure dose. UV1116 exhibited the best contrast as compared to AZ40XT and PMMA, while AZ40XT exhibited the highest sensitivity at low doses (<10μC/cm2). AFM analysis of the exposure pattern from radio-labelled cells and nuclei in UV1116 revealed a non-uniform distribution of 111In-EGF in the cell and nucleus, consistent with less well-resolved data from confocal microscopy and micro-autoradiography. [Copyright &y& Elsevier]

Internal radiotherapy using Auger-emitting radionuclides is a relatively new technique that presents interesting advantages with respect to external radiotherapy, such as localized tumor efficacy. The aim of this study was to assess the dosimetric effectiveness in irradiating a tumor partitioned in different phenotypes, with different radionuclides directed at each tumor phenotype: 99mTc, 125I, 161Tb, and 177Lu. State of the art Monte Carlo PENELOPE code and ICRP adult female reference voxel phantom (AFP) were used in order to mimic a lung tumor volume composed by four different phenotypes. For each radionuclide above mentioned, the decay modes (accessed through ICRP-107 data files) considered encompassed Auger electrons and β, X and ϒ radiation. Two main radiation therapy scenarios were simulated: i) the entire tumor was irradiated homogenously with each of the radionuclides; ii) each tumor phenotype was filled with a different radionuclide. The optimal dosimetric configuration was studied in terms of Dose Efficiency (DE), defined as tumor-to-healthy dose ratio. The Monte Carlo model was validated by comparing the results of SAF values in AFP and cellular S-values for 125I with the ones present in the bibliography. In the first scenario, calculations showed that the highest DE is reached by 125I. Namely, with 125I a gain dose factor (GDF) of about 2.8, 2.7 and 122.5 could be achieved, with respect to 177Lu, 161Tb, and 99mTc, respectively. In the second scenario, a combination of radionuclides directed to each of the phenotypes can act as enhancement for DE or dose in the tumor tissues, with respect to using only one radionuclide in the 4 tumor phenotypes. According to this study, the hypothetical use of different electron beam qualities directed to different tumor phenotypes of the same tumor could act as a radio-sensitizer and, at the same time, minimize dose to the surrounding healthy tissues. • Feasibility study about dose painting in Targeted Radionuclide Therapy. • Dosimetric assessment considering decays of 99mTc, 125I, 161Tb, and 177Lu. • LungTumor sub division in different volume phenotypes. • Combination of different radionuclides has a dose enhancement effect. • The highest dose to the tumor is achieved by beta radiation. [ABSTRACT FROM AUTHOR]

Microdosimetric calculations of the Auger electron emitter 123I were done in liquid water spheres using the Geant4 toolkit. The electron emission spectrum of 123I produced by Geant4 is presented. Energy deposition and corresponding S-values were calculated to investigate the influence of the sub-cellular localization of the Auger emitter. It was found that S-values calculated by the Geant4 toolkit are generally lower than the values calculated by other Monte Carlo codes for the 123I radionuclide. The differences in the compared S-values are mainly due to the different particle emission spectra employed by the respective computational codes and emphasizes the influence of the spectra on dosimetry calculations. [ABSTRACT FROM AUTHOR]