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At least 145 records · Page 8Linked to original sources

PubMed1985

Cellular fast-mixing techniques: possible applications with particle beams.

In the past cellular fast-mixing techniques have been used to investigate the time resolution of radiation processes that lead to modification of radiation response in bacterial and mammalian cellular systems. So far, published studies have been confined to effects with low-LET electron beams. The brief for this paper was to discuss where, and under what conditions, such a technique could be used to advantage with high-LET particle beams. Criteria for the experimental design, including conditions of flow rate, dose rate, and mixing times, are discussed. Radiobiological problems appropriate for applications of fast-particle beams are also discussed. These include studies to reveal possible multicomponents in cellular sensitization by oxygen and electron-affinic radiation sensitizers, studies designed to assist in the resolution of direct and indirect effects, and resolution of intracellular DNA damage.

Animals↗

PubMed1978

[Radiobiological bases and clinical aspects of radiation therapy with heavy particles (author's transl)].

Our present radiobiological knowledge gives rise to the hope of an amelioration of the local results in radiation therapy by means of new categories of radiations. Neutrons are clinically used to a larger extent already, protons occasionally. The physical characteristics of pi-meson beams are especially favorable. Even considerable ameliorations, however, of the percentage of local healing would increase the survival rate by some few per-cent only.

Elementary Particles↗

PubMed1985

W value measurements for 241Am alpha particles in various gases.

Measurements of W, the mean energy expended per ion pair formed, have been performed for 241Am alpha particles stopping in a number of the gases commonly used in ionisation chambers. Both absolute and relative measurements were made with nitrogen used as the reference gas for the relative measurements. The absolute method entailed a simultaneous measurement of a quantity of charge and the number of alpha particles which produced that charge, whilst the relative approach simply required a determination of the ratio of ion currents. Results were obtained for methane-based tissue-equivalent gas, for its constituents, i.e. methane, carbon dioxide and nitrogen, for argon, and also for a gas mixture with a composition approximately equivalent to A-150 plastic.

Americium↗

PubMed1975

An approach to microdosimetry in a pi- meson beam using nuclear emulsions.

K5 emulsions 10 mum thick were exposed at various depths in a perspex phantom to a 70 MeV pi- meson beam and counts taken of the tracks in emulsion volumes 7x7x10 mum3. Data are presented on the number of track events and also the total number of grains associated with each event in each of four categories spanning the LET range of the secondary particles. The number of heavy tracks (category 4) shows an increased incidence in the region of the stopping pi- mesons (14-5 cm in perspex) while the number of single grains (category 1) decreases with depth. Categories 2 and 3 (grain clusters and light tracks) are approximately constant with depth. An estimate of the grain sensitivity is obtained by taking the proton as representative of the whole range of secondary particles. This procedure gives a value of 5 keV per grain in the pi- peak. The LET of light tracks was therefore in the range 1-10 keV mum-1 in emulsion, scaling to 0-4-4 keV mum-1 in water. Heavy tracks have LET values in excess of 4 keV mum-1 in water.

Cobalt Radioisotopes↗

PubMedDate not supplied

Measurements and calculations of the influence of thin inhomogeneities on charged particle beams.

The predictions of an analytic technique for calculating fluence and dose distributions beneath thin inhomogeneities are presented for a number of structures, including a rectangular cavity or bar, a cylinder, a disk, and an angled or diffuse edge. Experiments with both electrons and protons for several geometries are presented and compared with predictions based on this technique. We offer some clinical guidelines for avoiding large perturbations due to scattering effects.

Elementary Particles↗

PubMed1982

Molecular and cellular radiobiology of heavy ions.

Quantitative studies at the BEVALAC have demonstrated some of the physical and radiobiological factors that promise to make accelerated heavy ions important for the therapy of cancer. The measured physical dose-biological effect relationships allow the safe and effective delivery of therapeutic schedules of heavy ions. Among the charged particle beams available, carbon, neon and helium ions in the "extended Bragg peak mode" have optimal physical and biological effectiveness for delivery of therapy to deep seated tumors. The depth-dose profiles of these beams protect intervening and adjacent tissues as well as tissues beyond the range of the particles. For the treatment of hypoxic tumors, silicon and argon beams are being considered because they significantly depress the radiobiological oxygen effect in the region of the extended Bragg ionization peak. The depth-effectiveness of the argon beam is somewhat limited, however, because of primary particle fragmentation. Silicon beams have a depth-dose profile which is intermediate between that of neon and argon, and are candidates to become the particle of choice for maximizing high LET particle effects. Heavy accelerated ions depress enzymatic repair mechanisms, decrease variations of radiosensitivity during the cell division cycle, cause greater than expected delays in cell division, and decrease the protective effects of neighboring cells in organized systems. Near the Bragg peak, enhancement of heavy particle effects are observed in split dose schedules. Late and carcinogenic effects are being studied. With the newly developed Repair-Misrepair theory we can quantitatively model most observations.

Animals↗

PubMed1980

Radiolysis of CoIII-EDTA solution by charged particles through 6Li(n,a)3H reaction.

This experiment was to study the radiolysis of CoIII-EDTA solution in 0.8N H2SO4 saturated with air by charged particles produced through 6Li(n,a)3H reaction. The experimental results show that the G(-CoIII-EDTA) decreases as the absorbed dose rate increases. For the same absorbed dose rate, the values of G(-CoIII-EDTA) are practically independent of absorbed dose. The effects of concentration and temperature are also studied.

Cobalt↗

PubMedDate not supplied

[Nonparametric method of determining the RBE coefficients of accelerated charged particles by the incidence of neoplasms in rats].

The nonparametric method was used to determine RBE coefficients of accelerated charged particles (helium ions of 4 GeV/nucleon and 645 MeV protons) by the incidence of tumors localized in different rat organs or by the absence of tumors. The nonparametric method permitted to find the dose dependence of the RBE coefficients and to make statistical analysis of the results obtained with due regard for come features of developing damages which were not revealed by conventional methods of determining RBE coefficients.

Animals↗

PubMed1997

Assessment of dose equivalent due to neutrinos.

Neutrinos are present in the natural environment and are also produced by particle accelerators. A recent hypothesis has also been proposed that asserts that ionizing radiation due to neutrinos from certain astronomical events may have led to the extinction of some biological species. Thus, it is of interest to be able to estimate the dose equivalent due to these weakly interacting particles. Presented here are methods for estimating the dose equivalent due to neutrinos over a broad domain of energy, examples of such calculations, and an assessment of the postulated role of neutrinos in biological extinctions. It is concluded that the dose equivalent due to neutrinos from natural sources and from present-day accelerators is inconsequential and the postulated role of neutrinos in biological extinctions is highly improbable.

Calcium↗

PubMed1982

The particles compared.

Figure 5 represents an updated attempt to represent the dose distribution and high LET advantages of the various heavy particles, summarizing the conclusions discussed above. Neutrons are the cheapest form of high LET radiation. Their biological properties are excelled only by argon ions, but of course, they yield quite ordinary dose distributions. Protons give the best physical dose distribution and are by far the cheapest charged particles. Their biological properties, however, are similar to gamma-rays. Pions are comparable to carbon and neon ions in dose effect distribution, but are not as good because of dose/rate limitations and a less sharp edge to the beam. Two principal questions remain: 1. Are super dose distributions worth the substantial cost? 2. Do hypoxic cells limit radiocurability? These questions can only be answered in clinical trials and cannot even be addressed in the radiobiology laboratory.

Argon↗

PubMed1975

RBE-dose relations for neutrons and pions.

From cellular radiosensitivity parameters and theoretical particle-energy spectra in tissue, of the secondary particles from neutron and negative pion irradiations, RBE-Dose relations have been calculated. The theoretical results are compared with clinical and radiobiological data for normal tissue, tumours and cells in culture. Formulae for calculation, cellular parameters and the needed properties of equivalent 'track-segment bombardments' are given, for several mammalian cells irradiated with pions and with neutrons of several energies.

Bone Marrow↗

PubMed1978

A heavy particle comparative study. Part II: cell survival versus depth.

Cell-survival measurements with depth of penetration were made for a series of incident doses of proton, helium, carbon, neon, argon, negative pion, neutron, and 60Co photon beams. Cultured human cells (T1) suspended in a gel-containing medium were used, and the measurements were found to be very useful in facilitating the design of ridge filters to produce iso-effects in the region of interest. Heavy charged particle beams (proton, helium, carbon, neon, and negative pion) were found to produce similar cell killing with depth of penetration. Because of saturation effects at higher LET, argon ions were less effective in killing aerated cells at depth, compared with other heavy charged-particle beams. Cell killing at depth in the region of interest, compared with that at the entrance, was not significantly different for single-field exposures when the Bragg peaks were broadened to cover a width of 10 cm. However, when two opposed fields with overlapping peaks were used, a large enhancement in killing was obtained in the peak region.

Argon↗

PubMed1982

Photon correlation spectroscopic study of the size distribution of phospholipid vesicles.

The dependence of phospholipid vesicle size on lipid composition is investigated by photon correlation spectroscopy. For each lipid composition prolonged ultracentrifugation was used to isolate a nearly uniform population of minimum-sized vesicles. The residual size variations in the samples were sufficient to cause polydispersity that made comparisons between samples difficult. Analyses of the data by the method of cumulants and by a method for approximating the particle size distributions directly are presented. The latter method made possible unambiguous comparisons that revealed small but systematic dependences of vesicle size on composition in vesicles containing mixtures of egg phosphatidylcholine and phosphatidylethanolamine, egg phosphatidylcholine and beef brain sphingomyelin, and in single lipid vesicles of egg phosphatidylcholine, dioleylphosphatidylcholine, and beef brain sphingomyelin. These size dependences are quantified within the resolution limits of the technique and their implications are discussed.

Animals↗

PubMed1976

Particle radiation therapy.

Particle radiation therapy has the potential for immediate and sustained favorable impact on management of the cancer patient by providing better local tumor control. Scientific knowledge and expertise are immediately available to mount effective clinical studies of fast neurons, protons, and helium ions, and to initiate necessary preliminary studies of pimesons and heavy ions. Meaningful studies will require a long-term commitment of support. The amount of support, although substantial, is not disproportionate to the potential benefit or existing support of other cancer research programs.

Elementary Particles↗

PubMed1982

Treatment of cancer with heavy charged particles.

A clinical radiotherapeutic trial using heavy charged particles in the treatment of human cancers has accrued over 400 patients since 1975, 378 of whom were treated with particles and 28 with low LET photons as control patients. Heavy charged particle radiotherapy offers the potential advantages of improved dose localization and/or enhanced biologic effect, depending on particle selected for treatment. Target sites have included selected head and neck tumors, ocular melanomata, malignant gliomata of the brain, carcinoma of the esophagus, carcinoma of the stomach, carcinoma of the pancreas, selected juxtaspinal tumors and other locally advanced, unresectable tumors. A Phase III prospective clinical trial has been started in carcinoma of the pancreas using helium ions. Phase I-II studies are underway with heavier particles such as carbon, neon and argon ions in order to prepare for prospective Phase III trials. Silicon ions are also under consideration for clinical trial. These studies are supported by the United States Department of Energy and National Institutes of Health.

Adult↗

PubMed1994

[Particle state: divided solids and functionality].

Physical and physico-mechanical properties of powder particles, in the field of pharmacy, as drugs, excipients, microparticles and so on... are one of the main element in quality of dosage forms. The aim of this work is to insist on the importance of packing and rheological properties of divided solids and on his influence on compacting behaviour in drug development and industrial process, to avoid difficulties due to the variability of physical properties batch to batch. But as the physical quality of material raw is induced up to the crystallization operation, it is necessary to know, before, what use it will be done.

Elementary Particles↗

PubMed1978

A heavy particle comparative study. Part I: depth-dose distributions.

The results of a comparative study of heavy particles of interest in radiotherapy, with peaks spread over a depth of 10 cm, are reported in four parts. The introduction to this study and the depth-dose distributions of the particles, (n, pi-, p, He, C, Ne, and Ar ions) are reported herein. The results indicate that protons give the best localization of dose. The degree of localization of dose with heavy ions is reduced with increasing charge on the ion. For ranges less than 15cm, heavier ions such as neon and argon still have favourable dose localization; however, for ranges in excess of 15 cm, heavy ions such as argon are unfavourable but superior to fast neutrons because penetration can be controlled by modulation of energy or range.

Argon↗

PubMed1983

Neutron doses in negative pion radiotherapy.

Absorbed neutron doses in regions outside the treatment volume from negative pion radiotherapy are presented, based on neutron spectral measurements for pions stopping in a tissue-equivalent target. A Monte Carlo neutron transport computer code was developed and used to calculate the absorbed dose as a function of the distance from the centre of the treatment volume. The Monte Carlo code, which is a modification of a neutron detector efficiency code, follows neutrons and gamma rays as they interact with either hydrogen or oxygen nuclei in a phantom. The code includes neutron elastic scattering on both hydrogen and oxygen as well as five inelastic nuclear reactions on oxygen. The recoil charged particles which provide the absorbed dose are considered until the neutron escapes the phantom or its kinetic energy falls below 1 ke V. Calculations of absorbed dose are compared with earlier dose calculations and measurements. Measurements of the neutron spectrum from a tissue-equivalent target indicate that the total kinetic energy carried away by neutrons is about 76 MeV, which is a significantly higher value than that used in earlier estimates of the neutron dose. The calculations presented here suggest that the neutron dose outside large treatment volumes may limit the use of negative pions for some therapeutic applications.

Elementary Particles↗