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Microdosimetry and Its Applications is an advanced textbook presenting the fundamental concepts and numerical aspects of the absorption of energy by matter exposed to ionizing radiation. It is the only comprehensive work on the subject that can be considered definitive. It provides a deeper understanding of the initial phase of the interaction of ionizing radiation with matter, especially biological matter, and its consequences.

Inhaltsverzeichnis

Frontmatter

Chapter I. Introduction

Abstract
In its action on matter, including living matter, ionizing radiation is uniquely efficient because it transfers energy to atoms in a highly concentrated form. The average energy absorbed per unit mass of irradiated medium, the absorbed dose, is minute compared to the energy densities that elicit comparable effects by other physical agents. The effectiveness of ionizations is further enhanced by their association in the tracks of charged particles. Depending on its microscopic distribution the energy required for a given level of biological injury may vary as much as a hundredfold between different ionizing radiations. Thus while the absorbed dose is a useful and standard quantity in the specification of irradiation, effects depend on the pattern in which a given amount of energy is deposited in the irradiated medium. A knowledge of such energy distributions is required not only in any explanations of the relative effectiveness of different kinds of ionizing radiation but it also can be expected to provide insight into the action of ionizing radiation in general. This has been recognized since the earliest days of radiobiology and led to the fundamental contributions by such investigators as Crowther, Dessauer, Timofeff-Resowsky, Zirkle and Lea.
Harald H. Rossi, Marco Zaider

Chapter II. Microdosimetric Quantities and their Moments

Abstract
The principal microdosimetric quantities: specific energy, z, and lineal energy, y, have been referred to in Sect. I.3. The formal definitions by the International Commission on Radiation Units and Measurements (ICRU, 1980) are:
Harald H. Rossi, Marco Zaider

Chapter III. Interactions of Particles with Matter

Overview
As already described, regional microdosimetry is concerned with the stochastics of energy deposition in specified sites. Once the target is defined as a physical ensemble (composition, geometry, etc) the problem is reduced to studying the probability of interaction of particles with the target system — an exercise in quantum mechanics.
Harald H. Rossi, Marco Zaider

Chapter IV. Experimental Microdosimetry

Abstract
The observation that ionizing radiations can differ greatly in effectiveness indicates that local concentrations of absorbed energy must be of cardinal importance. The obvious way of assigning a quantitative meaning to the term “local concentration of absorbed energy” is to define it as the energy absorbed in volumes of specified dimensions, and the dimensions of interest are those of the regions in the irradiated material where the concentration of absorbed energy determines the probability of a given effect. In preliminary treatments these regions can be regarded to be convex geometric volumes of equal size that are termed sites. Regional microdosimetry is concerned with energy deposition in sites and it is the principal object of experimental microdosimetry.
Harald H. Rossi, Marco Zaider

Chapter V. Theoretical Microdosimetry

Abstract
In Chapter II it was shown that the specific energy spectrum can be factorized in terms of a dose-dependent term and a z-dependent one. In regional microdosimetry a second factor that contributes to the shape of the microdosimetric distribution is the geometry of the site. The question then arises as to whether it would be possible to further factor out this contribution. This possibility is suggested by the fact that — in a homogeneous medium — one can regard the spectrum of energy deposition as resulting from the random overlap of two “objects”: the track (i.e. a collection of transfer points) and the site. As a matter of fact, this is precisely the way most theoretical microdosimetric distributions are generated, namely by randomly placing a site on a Monte-Carlo-generated track (see Section V.2). The interesting (and powerful) consequences of this viewpoint are examined in the following through a brief excursion in the domain of geometric probability. For a general introduction to this subject the book by Santalo (1976) may be consulted.
Harald H. Rossi, Marco Zaider

Chapter VI. Applications of Microdosimetry in Biology

Abstract
The interaction of ionizing radiation with matter is invariably followed by an involute chain of processes. Thus the chemical consequences of irradiation of as simple a substance as pure water are still not entirely understood. It might therefore appear to be futile to attempt to account for the observed effects on the vastly more complex biological organisms in terms of the pattern of absorption of radiant energy. The justification for useful activity in what has been termed radiation biophysics is that in all their intricacy biological processes can be governed by simple fundamental mechanisms. An outstanding example is Mendelian genetics in which the general rules of inheritance were identified. This preceded knowledge of the organization and indeed even of the existence of DNA.
Harald H. Rossi, Marco Zaider

Chapter VII. Other Applications

Abstract
In the application of microdosimetry to radiation biology a distinction needs to be made between direct and indirect effects (see section VI.1.5.2). In the case of direct effect of radiation the spatial pattern of altered target molecules is expected to coincide with that of the initial energy deposits44. In contrast, indirect action depends not only on the initial microdosimetric distribution (as represented, for example, by the radical species generated by radiation in the medium surrounding the target) but also on the probability that radicals that survive interactions among themselves diffuse and collide with the target molecule. Clearly the pattern of molecules modified indirectly is time dependent and not identical to that of the initial track. The qualitative features of these changes are illustrated in Fig.VII.1: the four panels (Turner et al, 1983) correspond to “snapshots” of the track of a 4 keV electron taken at times ranging from 1 psec to 0.1 μsec following passage through liquid water. During this time interval more than half of the initial radical species have reacted among themselves or have been converted to unreactive molecules; and one also notes the increasingly diffuse appearance of the track — in effect a decrease in the energy density of the track. Target molecules damaged indirectly by the track will have a spatial distribution that mimics the appearance of the track at the time of the reaction. This has important biological consequences: For instance, double strand breaks (dsb) in DNA result from the pairwise combination of single strand breaks (ssb) whenever they are within approximately 10 base pairs45. The relative distance between ssb-s produced in indirect action depends in turn on the pattern of hydroxyl radicals, OH, assumed to be the main species attacking the DNA molecule. In a medium containing scavengers of OH radicals — as is usually the case intracellularly — only OH radicals within several nanometers of the DNA may yield ssb-s; the others would have been scavenged earlier. Because of this the time available for diffusion is only several nanoseconds and, paradoxically, in the presence of a scavenger the probability of induced ssb-s to yield dsb-s is larger (compare second and fourth panels in Fig.VII.1). It has been hypothesized also that the spatial proximity of damaged targets may affect their chance of being enzymatically repaired in the cell.
Harald H. Rossi, Marco Zaider

Backmatter

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