A Monte Carlo study of cellularS-factors for 1 keV to 1 MeV electrons

Abstract

A systematic study of cellular S-factors and absorbed fractions for monoenergetic electrons of initial energy from 1 keV to 1 MeV is presented. The calculations are based on our in-house Monte Carlo codes which have been developed to simulate electron transport up to a few MeV using both event-by-event and condensed-history techniques. An extensive comparison with the MIRD tabulations is presented for spherical volumes of 1-10 microm radius and various source-to-target combinations relevant to the intracellular localization of the emitted electrons. When the primary electron range is comparable to the sphere radius, we find significantly higher values from the MIRD, while with increasing electron energy the escape of delta-rays leads gradually to the opposite effect. The largest differences with the MIRD are found for geometries where the target region is at some distance from the source region (e.g. surface-to-nucleus or cytoplasm-to-nucleus). The sensitivity of the results to different transport approximations is examined. The grouping of inelastic collisions is found adequate as long as delta-rays are explicitly simulated, while the inclusion of straggling for soft collisions has a negligible effect.

Monte Carlo single-cell dosimetry of I-131, I-125 and I-123 for targeted radioimmunotherapy of B-cell lymphoma

“…Thus, one should expect that the discrepancies will also depend on the cytoplasm dimensions; generally decreasing for a thinner cytoplasm (note that in the limit of a vanishing cytoplasm the N¬CS combination approaches the C¬CS geometry). This finding is less pronounced in the case of 131 I since, as expected, deviations decrease with increasing electron energy (Bousis et al 2009b).…”

“…These straggling distributions were here calculated specifically for water using our relativistic inelastic cross sections for water as described above. For electron energies above 10 keV, the present condensedhistory scheme provides cellular S-values that are within 5% of those of a detailed simulation (Bousis et al 2009b). Furthermore, dose-point-kernels and depth-dose-distributions in water up to 1 MeV electron energies are in good agreement with those obtained by other general-purpose codes (Bousis et al 2008a(Bousis et al , 2008b(Bousis et al , 2009a.…”

Cellular- and micro-dosimetry of heterogeneously distributed tritium

“…A comparison between present and MIRD results shows that they are almost identical for N←N (2.10% in difference) but quite different for N←Cy (30.55%) and N←CS (88.36%). A similar comparison for monoenergetic electrons is available (Bousis et al 2009) between MIRD results and MC results calculated using the event-by-event and condensed-history techniques. Note that the MIRD treatment does not include elastic interactions while the Penelope code does (Liu et al 2009).…”

“…All theoretical calculations, however, require the use of cross-section models to describe the interactions of low-energy electrons with water. Different models can sometimes lead to sizeable differences in the transport parameters that influence the subcellular dose (Nikjoo et al 2008, Bousis et al 2009). In the present work, MC Penelope (PENetration and Energy LOss of Positrins and Electrons) code (Salvat et al 2001) was used to compute the source-target geometry-dependent absorbed dose at the subcellular level.…”

The COOLER Code: A Novel Analytical Approach to Calculate Subcellular Energy Deposition by Internal Electron Emitters

“…Monte Carlo track-structure codes that simulate the electron slowing down process in an event-by-event manner can accurately describe the discrete nature of physical interactions, overcoming most of the deficiencies of the MIRD approach (25). Because detailed simulation of electron tracks can be time consuming, condensed history transport codes have often been employed to approach various cellular dosimetric problems (26)(27)(28)(29)(30)(31)(32).…”