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

Abstract

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.

Geant4-DNA modeling of nanodosimetric quantities in the Jet Counter for alpha particles

“…However, further work is required to study scaling procedure in different media, in nanoscale, as investigated by (Bug et al 2012), as well as in macroscale (voxelized patient geometry), when calibration of different tissue densities to water is applied in treatment planning. Previous work and our result demonstrate the validity of density scaling procedure that is essential for future application of experimental nanodosimetry for verification of particle therapy treatment plans that may be possible with currently designed compact nanodosimeters (Casiraghi andSchulte 2015, Vasi andSchneider 2021).…”

Ionization Detail Parameters for DNA Damage Evaluation in Charged Particle Radiotherapy: Simulation Study Based on Cell Survival Database

“…The possibility of the direct measurement of a biologically relevant nanodosimetric parameter is the key idea that drives the development of a small device that could be easily and routinely used in the clinical environment. The recent advancements in the thick-GEM technology [19,20] suggest that such a device can be proposed in a few years.…”

“…Such experimental setups are not unthinkable and were in fact proposed recently [22][23][24]. However, the level of complication of these experiments prevents the use of such methods in a clinical environment, especially given that miniaturized nanodosimeters still struggle to provide even a single target model [19,20]. In conclusion, since we cannot define any radiation quality factor in isolation from the properties of the biological system, we should take at least this minimal step and account for the finite probability p of converting an ionization into a lesion.…”

Quest for New Data: Ionizing Radiation Metrology in the Presence of Laser-Assisted Scattering Processes

“…Concretely, a simple attempt could be made for evidencing the effect of laser light on ionization-cluster formation, using a new experimental set-up recently employed for measuring cluster distributions. In [16], F. Vasi and U. Schneider reported a complete set of experimental data on the number of ionization clusters with increasing complexities -i.e., composed of an increasing number of ionizations that occurred close in space-formed by a 5 MeV alpha particle and measured with an innovative ceramic nanodosimeter.…”

“…The idea is that an end-user experimentalist could try to reproduce the measures reported in [16], adding a laser field interacting with the low-pressure propane ionized by the α-radiation of the Americium, and verifying if the size distribution of the ionization clusters, obtained with the Bayes theorem, does change. In our opinion, however, two important remarks must be made at this point: (i) first, the compact nanodosimeter employs low-pressure propane, which is know to have tissue-equivalent properties in the interaction with ionizing radiation, but the effect of the laser field on gaseous propane could not be the same as on liquid water; (ii) as reported above, the size distribution measured with the compact nanodosimeter is estimated using the Bayes theorem, which seems to induce a detection efficiency that decreases with the dimension of the sensitive volume, apparently posing a limit on the dimension of clusters that could be measured.…”