Nanodosimetry: Towards a New Concept of Radiation Quality

Abstract

The biological action of ionizing charged particles is initiated at the DNA level, and the effectiveness with which the initial physical effect changes into measurable biological damage is likely ruled by the stochastics of ionizations produced by the incident ions in subcellular nanometric volumes. Based on this hypothesis, experimental nanodosimetry aims at establishing a new concept of radiation quality that builds on measurable characteristics of the particle track structure at the nanometer scale. Three different nanodosimetric detection systems have been developed to date that allow measurements of the number of ionizations produced by the passage of a primary particle in a nanometer-size gas volume (in unit density scale). Within the Italian project MITRA (MIcrodosimetry and TRAck structure), funded by the Italian Istituto Nazionale di Fisica Nucleare (INFN) and the EMRP Joint Research Project 'BioQuaRT' (Biologically Weighted Quantities in Radiotherapy), experiments have been carried out, in which the frequency distribution of ionizations produced by proton and carbon ion beams of given energy was measured with the three nanodosimetric detectors. Descriptors of the track structure can be derived from these distributions. In particular, the first moment M1, representing the mean number of ionizations produced in the target volume, and the cumulative probability Fk of measuring a number ν ≥ k of ionizations. The correlation between measured nanodosimetric quantities and experimental radiobiological data available in the literature is here presented and discussed.

Simulating the nanometric track-structure of carbon ion beams in liquid water at energies relevant for hadrontherapy

“…Experimental nanodosimetry allows measuring the clustering of ionisation events in macroscopic gas-phase detectors having nanometric equivalent volumes of liquid water. Figure 4(c) shows by symbols the distributions of the cumulative probabilities F ionis n to produce clusters of size equal or larger than n (with n = 1, 2 or 3) as a function of the average ionisation cluster size M ionis 1 coming from a compilation of experimental data [18]. It is worth to mention that such a curve is universal, and independent of the dimensions and particularities of the nanodosimeters.…”

“…The cross section for the other major inelastic channel, namely dissociative electron attachment (DEA), is more difficult to calculate, and here is approximated from recommendations based on . Here lines represent the results of simulations, while symbols correspond to experimental nanodosimetric data [18].…”

“…From the simulations, the role of different physical mechanisms to the clustered nanometric biodamage can be assessed. The Monte Carlo simulations can also be checked against experimental nanodosimetric distributions for ionisation clusters, this interaction being the one which can be most easily measured in the laboratory [18].…”

Investigation into the foundations of the track-event theory of cell survival and the radiation action model based on nanodosimetry

“…This was later demonstrated to imply the one-to-one correspondence between the probability of two or more ionizations to apply only approximately and only for low-LET radiation (Nettelbeck and Rabus 2011;Rabus and Nettelbeck 2011). Conte et al (2017Conte et al ( , 2018 and Selva et al (2019) demonstrated that a link between nanodosimetry and cell survival can be based on cumulative probabilities of ionization ( 23)…”

“…The solid lines are Poisson distributions of the same average as the data represented by symbols. For details see text a role (Nettelbeck and Rabus 2011;Rabus and Nettelbeck 2011;Conte et al 2017Conte et al , 2018Selva et al 2019).…”