Local weighting of nanometric track structure properties in macroscopic voxel geometries for particle beam treatment planning

Alexander, F.G.; Villagrasa, C.; Rabus, Hans; Wilkens, Jan J.

doi:10.1088/0031-9155/60/23/9145

Cited by 10 publications

(12 citation statements)

References 24 publications

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“…In combination with a stopping power weighted method, the parametrization can be used to characterize the track structure of a mixed radiation field. 6,7 Conte et al were able to establish a relationship between nanodosimetric quantities and the coefficients of the linear-quadratic model. 8 The relative biological effectiveness can then be derived from the obtained linear-quadratic model parameters.…”

Section: Introductionmentioning

confidence: 99%

“…Alexander et al presented a track structure parametrization for protons and carbon ions in the energy range used clinically. In combination with a stopping power weighted method, the parametrization can be used to characterize the track structure of a mixed radiation field 6,7 . Conte et al were able to establish a relationship between nanodosimetric quantities and the coefficients of the linear‐quadratic model 8 .…”

Section: Introductionmentioning

confidence: 99%

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First measurements of ionization cluster‐size distributions with a compact nanodosimeter

Vasi

Schneider

2021

Medical Physics

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A nanodosimeter is a type of detector which measures single ionizations in a small gaseous volume in order to obtain ionization cluster size probability distributions for characterization of radiation types. Working nanodosimeter detectors are usually bulky machines which require a lot of space. In this work, the authors present a compact ceramic nanodosimeter detector and report on first measurements of cluster size distributions of 5 MeV alpha particles. Methods: Single ionization measurements are achieved by applying a weak electric field to collect positive ions in a hole in a ceramic plate. Inside the ceramic plate, due to a strong electric field, the ions are accelerated and produce impact-ionizations. The resulting electron avalanche is detected in a read-out electrode. A Bayesian unfolding algorithm is then applied to the experimentally obtained cluster size distributions to reconstruct the true cluster size distributions. Results: Experimentally obtained cluster size distributions by the compact nanodosimeter detector are presented. The reconstructed cluster size distributions agreed well with Monte Carlo simulated cluster size distributions for small volumes (diameter = 2.5 nm). For larger volumes, discrepancies between the reconstructed cluster size distributions and cluster size distributions from Monte Carlo simulations were observed. Conclusions: For the first time, ionization cluster size probability distributions could be obtained by a small and compact nanodosimeter detector. This signifies the achievement of a critical step toward the wide application of nanodosimetric characterization of radiation types including in clinical environments.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

First measurements of ionization cluster‐size distributions with a compact nanodosimeter

Vasi

Schneider

2021

Medical Physics

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“…It is still an open issue to resolve how these finding can be reconciled with the overwhelming evidence of the importance of indirect radiation effects (i.e. via radiation chemistry) and existing evidence of several relevant scales for radiation effectiveness [23].In fact, also the BioQuaRT project developed a multiscale model that included microdosimetry and nanodosimetry and the possibility of different relevant target sizes depending on the biological endpoint considered [17]. At least two similar approaches have been developed independently by other groups [24], [25].…”

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confidence: 99%

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confidence: 99%

Nanodosimetry – on the ''tracks'' of biological radiation effectiveness

Rabus¹

2020

Zeitschrift für Medizinische Physik

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It is well known that the biological effectiveness of a certain absorbed dose of ionizing radiation depends on the radiation quality, i. e. the spectrum of ionizing particles and their energy distribution [1], [2], [3]. As has been shown in several studies, the biological effectiveness is related to the pattern of energy deposits on the microscopic scale, the socalled track structure [4]. Clusters of lesions in the DNA molecule within site sizes of few nanometers play a particular role in this context [4], [5], [6]. A first approach to measure track structure of ionizing radiation with nanometric resolution was proposed already in 1975 [7]. However, the extension of microdosimetric measurements to site sizes of few nanometer dimension was facing the fundamental problem that in such small sites the number of interactions is too low, such that the assumption fails that the imparted energy is the number of ionizations multiplied by a simple conversion factor [8]. Therefore, the development of methods for measuring track structure details with nanometric resolution required a change of paradigm, namely restricting the characterization of track structure to its ionization component [9], [10].In should be noted in this context that the term nanodosimetry is used in the literature in different meanings. These include ongoing endeavors to extend microdosimetry into the nanometer range to below 100 nm site sizes [11], [12] as well as simulation studies of various kinds that are not focused on quantities that are directly measurable. In this paper we use the term nanodosimetry for studies of charged particle track structure, considering the stochastics of ionizations in nanometric targets.The quantity of interest is the relative frequency distribution of the so-called ionization cluster size, i.e. the number of ionizations inside a considered target (often called the 'site'). As is illustrated in Figure 1, the ionization cluster size distribution (ICSD) varies with the geometrical position of the target with respect to the particle track. Furthermore, it also depends on the size and composition of the target and, most importantly, on the radiation quality. The ICSD can also be characterized by its statistical moments or the complementary cumulative frequencies of ionization clusters exceeding a certain minimum size [13].Around the turn of the century, three different types of nanodosimeters have been developed to measure the frequency distribution of ionization cluster size [14]. All devices are gas counters that simulate nanometric sensitive volumes based on a density scaling principle [15]. They Figure 1. Schematic illustration of nanodosimetric ionization cluster size (ICS) distributions in a spread-out Bragg peak (SOBP) of protons in water. The orange spheres indicate the loci of ionizing interactions of the proton or of the emitted secondary electrons. The blue and red cylinders represent nanometric targets located in the core and in the penumbra region of the track, respectively. The histograms with the blue and red...

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“…Another approach proposed by Alexander et al 13 was to record conditional ionization cluster size distributions of protons in cylinders with a diameter of 2.3 nm and a height of 3.4 nm. Conditional cluster size distributions give the relative probability to obtain a cluster size since they disregard the cluster size zero.…”

Section: Introductionmentioning

confidence: 99%

Feasibility study of macroscopic simulations of nanodosimetric parameters for proton therapy

et al. 2020

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Purpose In view of the potential of treatment plan optimization based on nanodosimetric quantities, fast Monte Carlo methods for obtaining nanodosimetric quantities in macroscopic volumes are important. In this work, a “fast” method for obtaining nanodosimetric parameters from a clinical proton pencil beam in a macroscopic volume is compared with a slow and detailed method. Furthermore, the variations of these parameters, when obtained with the Monte Carlo codes TOPAS and NOREC, are investigated. Methods Monte Carlo track structure simulations of 1 keV–100 MeV protons and 12 eV–1 MeV electrons in a volume of 8 nm 3 liquid water provided us with an atlas of cluster size distributions. Two kinds of ionization cluster size distributions were recorded, counting all ionizations or only ionizations directly produced by the primary particle. The simulations of the proton pencil beam were performed in two different ways. A “fast” method where only the protons were simulated and a “slow and detailed” method where protons and electrons were simulated in order to obtain spectra at different depths. The obtained spectra were then convoluted with cluster size distributions. Results It was shown that the nanodosimetric quantity F2 from the “fast” method is, depending on the location, between 43.6% and 63.6% smaller than the F2 obtained by the “slow and detailed” method. However, it was also shown that variations of nanodosimetric quantities are even larger when the cluster size distributions of the electrons are simulated with the Monte Carlo code NOREC, that is, the cumulative F2 probabilities obtained with NOREC were between 50.8% and 75.5% smaller than the F2 probabilities obtained with TOPAS. Conclusions As long as the uncertainties of different Monte Carlo codes are not improved, it is feasible to only simulate protons in a macroscopic volume. It must be noted, however, that the uncertainty is in the order of 100%.

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Local weighting of nanometric track structure properties in macroscopic voxel geometries for particle beam treatment planning

Cited by 10 publications

References 24 publications

First measurements of ionization cluster‐size distributions with a compact nanodosimeter

First measurements of ionization cluster‐size distributions with a compact nanodosimeter

Nanodosimetry – on the ''tracks'' of biological radiation effectiveness

Feasibility study of macroscopic simulations of nanodosimetric parameters for proton therapy

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