Abstract
To understand the biological effects of radiation, it is important to determine how ionizing radiation deposits energy in micrometric targets. The energy deposited in a target located in an irradiated tissue is a function of several factors such as the radiation type and the irradiated volume size. We simulated the energy deposited by energetic ions in spherical targets of 1, 2, 4, and 8 µm radii encompassed in irradiated parallelepiped volumes of various sizes using the stochastic radiation track structure code Relativistic Ion Tracks (RITRACKS). Because cells are usually part of a tissue when they are irradiated, electrons originating from radiation tracks in neighboring volumes also contribute to energy deposition in the target. To account for this contribution, we used periodic boundary conditions in the simulations. We found that the single-ion spectra of energy deposition in targets comprises two components: the direct ion hits to the targets, which is identical in all irradiation conditions, and the contribution of hits from electrons from neighboring volumes, which depends on the irradiated volume. We also calculated an analytical expression of the indirect hit contributions using the local effect model, which showed results similar to those obtained with RITRACKS.
Highlights
Ionizing radiation, especially ions, is unique because it transfers energy on an atomic scale in a highly concentrated manner
The energy deposited by ionizing radiation is highly non-homogeneous due to the radiation track structure [1]
We simulated the irradiation of spherical targets of 1 μm radius and a box volume of 2 × 2 × 2 μm by one randomly incident single ion and calculated the average dose imparted to the target
Summary
Especially ions, is unique because it transfers energy on an atomic scale in a highly concentrated manner. While absorbed dose is a global quantity in the determination of radiation effects, the patterns of energy deposition provide a deeper understanding and basis for estimating the responses to ionizing radiation. Microdosimetry is the study and quantification of the spatial and temporal distribution of absorbed energy in irradiated matter volumes of dimensions in the micrometer range, such as cells or cellular organelles [2]. It focuses on the heterogeneous and stochastic nature of radiation and provides concepts and methods for measuring the associated physical quantities [3,4,5]. Microdosimetry has been used to estimate quality factors for risk assessment in radiation protection [6,7] and to quantify relative biological effectiveness using the microdosimetric kinetic model for planning treatments using hadron radiation therapy [8,9]
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