Abstract
The objective of microdosimetry was, and still is, to identify physical descriptions of the initial physical processes of ionising radiation interacting with biological matter which correlate with observed radiobiological effects with a view to improve the understanding of radiobiological mechanisms and effects. The introduction of therapy with particles starting with fast neutrons followed by negative pions, protons and light ions necessitated the application of biological weighting factors for absorbed dose in order to account for differences of the relative biological effectiveness (RBE). Dedicated radiobiological experiments in therapy beams with mammalian cells and with laboratory animals provided sets of RBE values which are used to evaluate empirical 'clinical RBE values'. The combination of such experiments with microdosimetric measurements in identical conditions offered the possibility to establish semi-empirical relationships between microdosimetric parameters and results of RBE studies.
Highlights
Microdosimetry in its original meaning started more than 50 y ago with the development and the use of low-pressure, tissue-equivalent proportional counters by H.H
Experimental microdosimetry with Rossi Counters enables the measurement and quantification of the energy imparted by single primary particles (‘single events’) in microscopic volumes with dimensions similar to that of biological entities such as cells or cell nuclei
Absorbed dose is the fundamental quantity in radiation therapy
Summary
Microdosimetry in its original meaning started more than 50 y ago with the development and the use of low-pressure, tissue-equivalent proportional counters by H.H. Rossi (‘Rossi Counters’) (Figure 1)(1). Experimental microdosimetry with Rossi Counters enables the measurement and quantification of the energy imparted by single primary particles (‘single events’) in microscopic volumes with dimensions similar to that of biological entities such as cells or cell nuclei. The counters simulate biological matter of linear dimensions of the order of micrometre by using tissue-equivalent material for the counter walls and low-pressure tissue-equivalent counting gas. The pulse-height distributions correspond to energy deposition distributions in the simulated microscopic volume. This technique provided a new set of data that could be compared with data obtained in LET computation developed at the same period.
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