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PubMedDate not supplied

[Induction of gene and deletion mutations by accelerated heavy charged particles in Escherichia coli cells].

The results of the induction of the point and the deletion mutations by the radiation with broad region of linear energy transfer (LET) ox Escherichia coli cells. The linear-quadratic function for point mutation induction was shown in comparison with linear dependence for deletion mutations. The relative biological effectiveness (RBE) is described as a function of LET by dependence with a local maximum. The greatest RBE coefficients for the lethal effects, gene and deletion mutation induction realize under different LET of heavy charged particles.

Alpha Particles↗
PubMed1978

[Medical applications of cyclotrons (author's transl)].

Isochronous cyclotrons used to accelerate different charge particles (protons, deuterons, alphas...) at variable energies, have important medical applications, for neutron teletherapy, in vivo or in vitro activation analysis or production of short-lived radioisotopes for nuclear medicine. The characteristics of the cyclotron presently available are described for these three applications (low energy "compact" cyclotrons, cyclotrons of intermediate and high energies), and their advantages are discussed from the points of view of the medical requirements, the financial investments and the results obtained.

Activation Analysis↗
PubMed2004

[Conception of heavy ion beam therapy at Heidelberg University (HICAT)].

The ion beam therapy facility HICAT presently under construction at the Heidelberg University Clinic will be the first clinical irradiation facility for heavy ions in Europe. Its capacity should enable the treatment of 1000 patients per year. The use of different ion species ranging from protons to oxygen under identical conditions should clarify the question of which particle species is best suited in terms of indication. A synchrotron will accelerate the particles to energies corresponding to water-equivalent ranges from 2 cm to 30 cm. An intensity-controlled raster scanning technique will be used to optimize the use of the favorable depth dose distribution of ions. The planned heavy-ion gantry will be the first world-wide. The facility should be complete in 2006.

Equipment Design↗
PubMed2000

Backscatter towards the monitor ion chamber in high-energy photon and electron beams: charge integration versus Monte Carlo simulation.

In some linear accelerators, the charge collected by the monitor ion chamber is partly caused by backscattered particles from accelerator components downstream from the chamber. This influences the output of the accelerator and also has to be taken into account when output factors are derived from Monte Carlo simulations. In this work, the contribution of backscattered particles to the monitor ion chamber response of a Varian 2100C linac was determined for photon beams (6, 10 MV) and for electron beams (6, 12, 20 MeV). The experimental procedure consisted of charge integration from the target in a photon beam or from the monitor ion chamber in electron beams. The Monte Carlo code EGS4/BEAM was used to study the contribution of backscattered particles to the dose deposited in the monitor ion chamber. Both measurements and simulations showed a linear increase in backscatter fraction with decreasing field size for photon and electron beams. For 6 MV and 10 MV photon beams, a 2-3% increase in backscatter was obtained for a 0.5 x 0.5 cm2 field compared to a 40 x 40 cm2 field. The results for the 6 MV beam were slightly higher than for the 10 MV beam. For electron beams (6, 12, 20 MeV), an increase of similar magnitude was obtained from measurements and simulations for 6 MeV electrons. For higher energy electron beams a smaller increase in backscatter fraction was found. The problem is of less importance for electron beams since large variations of field size for a single electron energy usually do not occur.

Electrons↗
PubMed1986

Early alveolar clearance of particles in rabbits undergoing acute and subchronic exposure to ozone.

The concentration-response relationship for changes in early alveolar clearance resulting from O3 inhalation were investigated. Groups of five rabbits were exposed to 0.0, 0.1, 0.6, or 1.2 ppm O3, 2 hr/day X 1 day; or to 0.0, 0.1, or 0.6 ppm O3, 2 hr/day X 13 days. Following the initial O3 exposure all rabbits inhaled an aerosol of 85Sr-tagged, 3.0-micron, polystyrene latex particles and particle retention was determined daily for the following 14 days. Single exposures to O3 produced a concentration related trend from accelerated clearance at 0.1 ppm to a transient impairment of clearance at 1.2 ppm. Subchronic exposure resulted in a significant acceleration of particle clearance at both 0.1 and 0.6 ppm, with the effect more pronounced at the higher level. These results demonstrate that single or repeated exposure of rabbits to 0.1 ppm O3, a level below the current National Ambient Air Quality Standard, produces alterations in early alveolar clearance. The effects observed at higher levels of O3 appeared to depend on both the concentration and exposure regime; acute exposures produced a concentration related trend toward an initial retardation of clearance, which was followed by an acceleration in particle removal, while repeated exposures resulted in a persistent acceleration of clearance.

Animals↗
PubMed2000

Evaluation of the contribution of capture gamma rays, x-ray leakage, and scatter to the photon dose at the maze door for a high energy medical electron accelerator using a Monte Carlo particle transport code.

A Monte Carlo simulation of the photon dose due to scattered x rays, head leakage photons, and capture gamma rays in the maze of an 18 MeV accelerator facility was carried out. The results of the Monte Carlo simulation were compared with dose measurements made in the maze and also with values calculated using an empirical equation. Agreement within +/-26% was found among the three techniques used to evaluate the capture gamma ray dose. It was found that the empirical equation overestimated the scattered x ray plus head leakage photon dose by a factor as large as 2.9 as compared to the other methods. It was concluded that the photon dose, for mazes greater than 3 m in length, is produced predominately by capture gamma rays.

Biophysical Phenomena↗