Review of the Geant4-DNA Simulation Toolkit for Radiobiological Applications at the Cellular and DNA Level

The Geant4-DNA low energy extension of the Geant4 Monte Carlo (MC) toolkit is a continuously evolving MC simulation code permitting mechanistic studies of cellular radiobiological effects. Geant4-DNA considers the physical, chemical, and biological stages of the action of ionizing radiation (in the form of x- and γ-ray photons, electrons and β±-rays, hadrons, α-particles, and a set of heavier ions) in living cells towards a variety of applications ranging from predicting radiotherapy outcomes to radiation protection both on earth and in space. In this work, we provide a brief, yet concise, overview of the progress that has been achieved so far concerning the different physical, physicochemical, chemical, and biological models implemented into Geant4-DNA, highlighting the latest developments. Specifically, the “dnadamage1” and “molecularDNA” applications which enable, for the first time within an open-source platform, quantitative predictions of early DNA damage in terms of single-strand-breaks (SSBs), double-strand-breaks (DSBs), and more complex clustered lesions for different DNA structures ranging from the nucleotide level to the entire genome. These developments are critically presented and discussed along with key benchmarking results. The Geant4-DNA toolkit, through its different set of models and functionalities, offers unique capabilities for elucidating the problem of radiation quality or the relative biological effectiveness (RBE) of different ionizing radiations which underlines nearly the whole spectrum of radiotherapeutic modalities, from external high-energy hadron beams to internal low-energy gamma and beta emitters that are used in brachytherapy sources and radiopharmaceuticals, respectively.

Measurement of Natural Radionuclides in Drinking Water and Risk Assessment in a Volcanic Region of Italy, Campania

The physical–chemical properties of water are closely linked to the geological nature of the site where they are located. This aspect becomes even more interesting when analyzing the natural radionuclides in the drinking water of a volcanic territory such as Campania in southern Italy. This study concerned the measurement of activity concentration of gross alpha and beta, radon, and tritium to evaluate their biological impact. The measurements were carried out using alpha spectrometry for alpha emitters, proportional counter for beta emitters, the electret system for radon in water, and finally liquid scintillation for the measurement of tritium concentration. The biological impact was assessed considering the indicative dose, if applicable, and the effective annual dose of radon. Although the results show that the values are below international and national references, the radiological characterization of drinking water is of fundamental importance to optimize the radiation protection of the population.

Development of multi-systems for measurement of radionuclide absolute activity

The development of a multi-systems triple-to-double coincidence ratio (TDCR) and coincidence 4pb-g methods, based on liquid scintillation to radionuclide standardization is presented in this work. The adjustments of multi-systems were made using standards of 3H and 14C and 60Co. The initial stage was performing measurements of pure beta-emitters 3H, 63Ni, and 90Sr90Y standard solutions by TDCR. The results were consistent within the standard uncertainty. Measurements will be performed with a beta-gamma 60Co in a comparison to the SIR / BIPM to assess the multi-system's performance.

Concerning the Tritium Dose at the Cellular Level

Purpose: To adapt traditional method of soft beta emitters’ dose calculation to the individual biological cells, to estimate the value of absorbed dose-rate factors for different tritium compounds on a cellular level. Material and methods: Approximation for point-source function obtained by L.V. Timofeev, G.B. Radzievsky et al. was used to adapt macroscopic beta-particle dosimetry methods to the area of subcellular structures. Results: Using the introduced concept of irradiated cell model base states the analytical expressions for absorbed dose in subcellular structures were suggested for non-uniform activity distributions of soft beta emitters in human tissue. The values of absorbed dose-rate factors for the case of organically bounded tritium confined to the nucleus (1.8 mGy/decay for 3H-thymidine) and for the case of tritiated water uniformly distributed throughout tissue (3.510-3 mGy/decay) were obtained. Conclusion: It can be assumed that traditional method of soft beta emitters’ dose calculation is adapted to the individual biological cells. The proposed methodology is supposed to be used in the future when constructing, based on experimental data, a biokinetic model of the intake of tritium organic compounds in the human body.

The Simulated Characterization and Suitability of Semiconductor Detectors for Strontium 90 Assay in Groundwater

This paper examines the potential deployment of a 10 mm × 10 mm × 1 mm cadmium telluride detector for strontium-90 measurement in groundwater boreholes at nuclear decommissioning sites. Geant4 simulation was used to model the deployment of the detector in a borehole monitoring contaminated groundwater. It was found that the detector was sensitive to strontium-90, yttrium-90, caesium-137, and potassium-40 decay, some of the significant beta emitters found at Sellafield. However, the device showed no sensitivity to carbon-14 decay, due to the inability of the weak beta emission to penetrate both the groundwater and the detector shielding. The limit of detection for such a sensor when looking at solely strontium-90 decay was calculated as 323 BqL−1 after a 1-h measurement and 66 BqL−1 after a 24-h measurement. A gallium-arsenide (GaAs) sensor with twice the surface area, but 0.3% of the thickness was modelled for comparison. Using this sensor, sensitivity was increased, such that the limit of detection for strontium-90 was 91 BqL−1 after 1 h and 18 BqL−1 after 24 h. However, this sensor sacrifices the potential to identify the present radionuclides by their end-point energy. Additionally, the feasibility of using flexible detectors based on solar cell designs to maximise the surface area of detectors has been modelled.

APPLICATION OF METHODS OF STANDARDIZATION OF BETA-RADIATION SPECTRUM IN LIQUID-SCINTILLATION TREATMENT

The features of beta spectra standardization for modern liquid scintillation counting (LSC) us-ing Quantulus 1220TM alpha beta spectrometer are considered. The range of tasks is tritium meas-urement, beta-spectrometric determination of strontium-90, determination of strontium-90 by Che-renkov counting, determination of lead-210 in aerosol filters, radiocarbon studies. The purpose of the study was to summarize and analyze the peculiarities of the application of the methods of spectra standardization of beta-emitters in the study of radioactivity of environmental objects based on liquid scintillation counting. Materials and methods: liquid scintillation counting, LSC, Cherenkov counting, radiochemi-cal preparation of samples, spectra decomposition of beta-emitters. Results: Methods for spectra standardization of beta-emitters samples were analyzed in the study of 3H, 14C, 90Sr, 210Pb in environmental objects using a modern Quantulus 1220TM liquid scintil-lation spectrometer. The acceptability, effectiveness and scope of application of the methods of stand-ardization and spectra decomposition for beta-emitters for liquid scintillation counting and Cerenkov counting are grounded.