Comparison of GEANT4 very low energy cross section models with experimental data in water.

PURPOSE: The GEANT4 general-purpose Monte Carlo simulation toolkit is able to simulate physical interaction processes of electrons, hydrogen and helium atoms with charge states (H0, H+) and (He0, He+, He2+), respectively, in liquid water, the main component of biological systems, down to the electron volt regime and the submicrometer scale, providing GEANT4 users with the so-called "GEANT4-DNA" physics models suitable for microdosimetry simulation applications. The corresponding software has been recently re-engineered in order to provide GEANT4 users with a coherent and unique approach to the simulation of electromagnetic interactions within the GEANT4 toolkit framework (since GEANT4 version 9.3 beta). This work presents a quantitative comparison of these physics models with a collection of experimental data in water collected from the literature. METHODS: An evaluation of the closeness between the total and differential cross section models available in the GEANT4 toolkit for microdosimetry and experimental reference data is performed using a dedicated statistical toolkit that includes the Kolmogorov-Smirnov statistical test. The authors used experimental data acquired in water vapor as direct measurements in the liquid phase are not yet available in the literature. Comparisons with several recommendations are also presented. RESULTS: The authors have assessed the compatibility of experimental data with GEANT4 microdosimetry models by means of quantitative methods. The results show that microdosimetric measurements in liquid water are necessary to assess quantitatively the validity of the software implementation for the liquid water phase. Nevertheless, a comparison with existing experimental data in water vapor provides a qualitative appreciation of the plausibility of the simulation models. The existing reference data themselves should undergo a critical interpretation and selection, as some of the series exhibit significant deviations from each other. CONCLUSIONS: The GEANT4-DNA physics models available in the GEANT4 toolkit have been compared in this article to available experimental data in the water vapor phase as well as to several published recommendations on the mass stopping power. These models represent a first step in the extension of the GEANT4 Monte Carlo toolkit to the simulation of biological effects of ionizing radiation.

[Commuting accidents: the influence of excessive daytime sleepiness. A review of an Italian Police officers population]. / Infortuni in itinere: ruolo della sonnolenza in una popolazione di operatori della Polizia di Stato.

Commuting accidents (CA) play an important role in many systems of workers' compensation insurance and with good reason, as they generally bring about more serious consequences in terms of permanent disablement and death than ordinary occupational accidents; this usually leads to high social costs. Nevertheless, research investigations aimed at studying the possible causes underlying the phenomenon are not available in medical literature. Objective of the present study is to evaluate whether excessive daytime sleepiness (EDS) might influence the occurrence of CA. 463 CA occurred to 411 police officers in northern Italy during the period 1999 - 2002 were collected; 51.9% of the subjects were working on shifts, 48.1% were non-shift workers. The study was carried out by submitting a self-administered questionnaire to gather information on age and physical characteristics, working conditions, sleep-related problems and accidents occurrence; EDS was measured by the Epworth Sleepiness Scale (ESS). A large number of workers (36%) complained of EDS; a strict significant relationship between shift - work condition and the presence of EDS was found, thus suggesting that CA are significantly influenced by EDS. The shift work schedule adopted by Italian Police might be accountable for the disruption of the balance between circadian and homeostatic factors.

[Shift-work seniority increases the severity of sleep disorders. Comparison of different categories of shift-workers]. / L'anzianità di turnismo aumenta la gravità dei disturbi del sonno. Confronto fra diverse categorie di turnisti.

Shift-work disrupts the sleep-wake cycle and could bring about sleep disorders and excessive daytime sleepiness. We studied two samples of shift-workers, a group of 178 nurses and one of 174 police officers, all working in the town of Palermo (Italy); their answers to a sleep disorder questionnaire were scored and added in order to create a Sleep Disorder Score (SDS). The SDS cut-off value, discrimining pathological values from physiological ones, was settled a-priori. In both groups SDS did not depend on sex, age, weight, height nor on working seniority, but it increased non linearly (cubic form) with shift-work seniority. In nurses this mathematical description of SDS exceeded the cut-off value after 15 years of shift-work seniority; in police officers it settled asymptotically under the critical value. This could be ascribable both to the different composition in sex of the two samples (nurses: 49% F-51% M vs. police officers: 6% F-94% M) both to the self-selection process that seems to undergo police officers (nurses do not leave shift-work because of salary incentives).

Dose point kernels in liquid water: an intra-comparison between GEANT4-DNA and a variety of Monte Carlo codes.

Modeling the radio-induced effects in biological medium still requires accurate physics models to describe the interactions induced by all the charged particles present in the irradiated medium in detail. These interactions include inelastic as well as elastic processes. To check the accuracy of the very low energy models recently implemented into the GEANT4 toolkit for modeling the electron slowing-down in liquid water, the simulation of electron dose point kernels remains the preferential test. In this context, we here report normalized radial dose profiles, for mono-energetic point sources, computed in liquid water by using the very low energy "GEANT4-DNA" physics processes available in the GEANT4 toolkit. In the present study, we report an extensive intra-comparison of profiles obtained by a large selection of existing and well-documented Monte-Carlo codes, namely, EGSnrc, PENELOPE, CPA100, FLUKA and MCNPX.

Molecular scale track structure simulations in liquid water using the Geant4-DNA Monte-Carlo processes.

This paper presents a study of energy deposits induced by ionising particles in liquid water at the molecular scale. Particles track structures were generated using the Geant4-DNA processes of the Geant4 Monte-Carlo toolkit. These processes cover electrons (0.025 eV-1 MeV), protons (1 keV-100 MeV), hydrogen atoms (1 keV-100 MeV) and alpha particles (10 keV-40 MeV) including their different charge states. Electron ranges and lineal energies for protons were calculated in nanometric and micrometric volumes.

Sleepiness in a population of Italian shiftwork policemen.

The aim of this study was to evaluate the effects of shiftwork on sleepiness, sleep disorders and sleep related accidents in a population of policemen. Data concerning age and physical characteristics, working conditions, sleep problems and accidents were collected by a questionnaire. Sleepiness was evaluated by the Epworth Sleepiness Scale (ESS) while the presence of sleep disorders was evaluated by a score (SD-score) drawn from indicators of insomnia, breathing disorders, periodic limb movements-restless leg syndrome and hypersomnia. The effects of age, gender, body mass index, working condition and seniority on ESS, SD-score and accidents were analysed by linear and logistic regression. Participants were 1280 policemen: 611 shiftworkers and 669 non-shiftworkers. The ESS scores were not higher in shiftworkers than in non-shiftworkers, but the SD-score was found to be significantly influenced by shiftwork condition and seniority. The occurrence of sleep-related accidents was found to have been significantly increased for shiftworkers and related to the presence of indicators of sleep disorders. The sleepiness could be underestimated or even overcome by the influence of stressing conditions. However our data should alert occupational health physicians for the diagnosis and prevention of possible lurking intrinsic sleep disorders likely to influence health problems and risk of accidents in shiftworkers.