PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Particle Accelerators”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1989

[Dependence of the incidence of the occurrence of ovarian and uterine tumors in rats on the irradiation dosage from accelerated particles and gamma rays].

The incidence rate of ovarian and uterine tumours in rats after irradiation by protons with the energy of 645 MeV, 9 GeV and He2+ has been studied. The tumour rate is shown to increase with the radiation dose. The character of the dose-response for tumours of two sites is different. A relative risk of ovarian tumour incidence after He2+ exposure is twice as high as after other types of radiation.

Animals↗
PubMed1977

On a simple method for routine check of the constancy of radiation quality of bremsstrahlung emitted by therapeutic particle accelerators.

The constancy of radiation quality of therapeutically employed particle accelerators has to be checked at weekly intervals. Any change in radiation quality may have considerable therapeutic effects owing to its influence on dose distribution. It can be recommended to make measurements instead of, or in addition to, the axial reference-point measurement at 5 and 15 cm depth in the phantom, at 5 cm depth in the beam axis and at a reference-point about 1 cm within the geometric edge of the field, for checking the constancy of the radiation quality of bremsstrahlung. Only then, if routine checks carried out for the axial and the lateral reference-point dose ratios do not show any deviations greater than e.g. +/- 2%, radiation quality is deemed to have remained sufficiently constant for radiotherapeutical applications.

Radiotherapy, High-Energy↗
PubMed1985

[The management of particle accelerators in radiotherapy].

In this multicentric survey, the management costs and the technical problems connected with the use of electron accelerators in Radiotherapy are studied. The data were collected by a proper questionnaire and concern 11/35 accelerators in use in Italy, in public hospitals, during the period 1982-1983. The average purchase cost of an accelerator was 1113 milions lire and the amortization cost is 111 milions lire per year. The expenses for the amortization of the cost of the bunker, for ordinary and extraordinary maintenance, for the employed staff and for the electric power respectively, represent the 22%, 5%, 43% and 2% of the total management cost (395 milions lire per year). In 1983 the load per machine was 400 patients and the cost per patient was 1 milion lire. On the average, 4 years are needed from the order to the beginning of the treatments with large differences among centers. The machines average use is 7.1 hours a day and keep 2.8 technicians busy per week. The time wasted by repairs or maintenances increases (+7%) the average duration of stay in hospital of patients. An attentive evaluation of the studied parameters allows us to single out the most significant variables on which is possible to work to increase the efficiency and to reduce the management costs of an accelerator.

Cost-Benefit Analysis↗
PubMedDate not supplied

[Evaluation of biological effectiveness of high-energy accelerated particles based on the study of cytogenetic disorders in murine sex cells].

The frequency of reciprocal translocations in spermatogonia of F1(CBAxC57Bl6) mice irradiated with 50 MeV protons, 4.2 GeV deuterons, 1.8 GeV/nucleon helium ions or 60Co gamma-rays was investigated. The relative biological effectiveness of these particles calculated by comparing the equieffective doses of reference and experimental radiations was less than 1.0 under the assumption of the linear dose-effect relationship. The RBE of the particles calculated by means of the nonparametric method largely depended on the doses applied.

Animals↗
PubMed1991

Accelerated heavy particles and the lens. VI. RBE studies at low doses.

We report on the prevalence, hazard, and relative biological effectiveness (RBE) for various stages of lens opacification in rats induced by very low doses of fast argon ions of LET 88 keV/microns, compared to those for X rays. Doses of argon ions from 0.01 to 0.25 Gy were used and RBEs of these ions relative to X rays estimated using a nonparametric technique. At the end of the follow-up period, which encompasses a significant fraction of the animals' lifetime, 90% confidence intervals for the RBE of the argon ions relative to X rays were 4-8 at 0.25 Gy, 10-40 at 0.05 Gy, and 50-100 at 0.01 Gy. Our results are consistent with the point-estimate neutron RBEs in Japanese A-bomb survivors, though broad confidence bounds are present in the Japanese results. If a reasonable extrapolation to higher doses is used, our results are also consistent with data reported earlier at higher doses for argon-ion cataractogenesis in rats, mice, and rabbits. We conclude from these results that at very low doses the RBE for cataractogenesis from HZE particles in space is considerably more than 20, and use of a quality factor of at least 50 would be prudent.

Animals↗
PubMed1989

Accelerated heavy particles and the lens. III. Cataract enhancement by dose fractionation.

For a number of biological end points it has been shown that, in contrast to low linear energy transfer (LET) radiation, dose fractionation of high-LET radiation does not result in a reduction in overall effectiveness. Studies were conducted to determine the effect of fractionating the exposures to heavy ion doses on the development of cataracts. Rat eyes were exposed to single doses of 1, 5, and 25 cGy of 570 MeV/amu40Ar ions and to 2, 4, and 10 Gy of 250 kVp X rays. These were compared to unirradiated controls and eyes which were exposed to the same total dose delivered in four fractions over 12 h. While in all cases fractionation of the exposure to X rays produced significant reduction in cataractogenic potential, fractionating doses of 40Ar ions caused a dose- and stage-dependent enhancement in the development of cataracts.

Animals↗
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↗
PubMed1986

Accelerated heavy particles and the lens II. Cytopathological changes.

To assess more fully the risk to normal tissue exposed to accelerated heavy particles in the space program and during radiotherapy on earth, the cytopathological effects of a variety of doses of accelerated (570 MeV/amu) Argon (40Ar) ions on the rat lens were investigated. Time-course analyses of lenses exposed to a 1 Gy (100 rad)-dose revealed that the effects of the particles on mitotic index, nuclear fragmentation, and meridional row (MR) cytoarchitecture were qualitatively similar to those caused by 185 kVp x-rays. The effects of dose on the lens epithelium was also examined at 67 wk post-irradiation. The mitotic index returned to normal levels by that time; however, the biological effectiveness (RBE) of 40Ar relative to x-rays, in causing MR disorganization, increased with decreasing dose and closely resembled the RBE for cataractogenesis. The RBE data are consonant with the view that radiation cataracts are the result of damage to the lens epithelial population, which is later expressed as aberrant differentiation during fibergenesis.

Animals↗
PubMed1988

Accelerated heavy particles and the lens. V. Theoretical basis of cataract enhancement by dose fractionation.

That accelerated heavy ions are highly cataractogenic is indisputable. The basis of heavy particle effectiveness and the augmentation by fractionation, as recently demonstrated, remains less clear. There is no question, however, that these are tied to the 'track structure' and densely ionizing nature of the radiation. The unique energy deposition characteristics relating to charge and track structure are now being explored to begin to dissect the cellular response of the lens epithelium to radiation exposure. The elucidation of the basis of the cataractogenic effect of accelerated heavy ions is important not only to risk assessment, but also in the consideration of theories of radiation action and the mechanism of cortical opacification arising from a myriad of cataractotoxic agents.

Animals↗
PubMed1991

Therapeutic radionuclides: production and decay property considerations.

The development of effective therapeutic radiopharmaceuticals requires careful consideration in the selection of the radionuclide. The in vivo targeting and clearance properties of the carrier molecule must be balanced with the decay properties of the attached radionuclide. Radionuclides for therapeutic applications fall into three general categories: beta-particle emitters, alpha-particle emitters, and Auger and Coster-Kronig-electron emitters following electron capture. Alpha particles and Auger electrons deposit their energy over short distances with a high LET that limits the ability of cells to repair damage to DNA. Despite their high levels of cytotoxicity, the relatively short range of alpha particles requires binding of the carrier molecule to most cancer cells within a tumor in order to be effective. Because of the extremely short range of Auger electrons, the radionuclide must be carried directly into the nucleus to elicit high radiotoxicity, making it necessary to deliver the radionuclide to every cell within a tumor cell population. These characteristics impose rigid restrictions on the nature of the carrier molecules for these types of particle emitters but successful targeting of these types of radionuclides could result in high therapeutic ratios. Most beta-emitting radionuclides are produced in nuclear rectors via neutron capture reactions; however, a few are produced in charged-particle accelerators. For radionuclides produced by direct neutron activation, the quantities and specific activities that can be produced are determined in large part by the cross-section of the target isotope and the flux of the reactor. Many applications (e.g., therapeutic bone agents, radiolabeled microspheres, radiocolloids) do not require high-specific activities and can therefore utilize the wide range of radionuclides that can be produced in sufficient quantity by direct neutron activation. Other applications (e.g., MAb labeling) require high-specific activity radionuclides in order to deliver a sufficient number of radionuclide atoms to the target site without saturating the target or compromising the integrity of the carrier molecule. Most radionuclides, produced at NCA levels in reactors, are produced via indirect reactions. High-specific activity beta emitters can also be obtained from radionuclide generator systems where the longer-lived parent radionuclide may be obtained from direct neutron activation, as a fission product, or from charged-particle accelerators. It is essential that the half-life of a radionuclide used in RNT be compatible with the rates of localization in target tissues and clearance of the carrier molecule from normal tissues. This consideration is especially important for the various MAbs and their fragments that are currently under investigation as carrier molecules to RIT.(ABSTRACT TRUNCATED AT 400 WORDS)

Half-Life↗
PubMed1986

Detection of infrasound by the Atlantic cod.

Below about 50 kHz the level of ambient noise in the sea increases continuously towards lower frequencies. In the infrasound range the spectral slope is particularly steep. This low-frequency noise may propagate long distances with little attenuation, causing a directional pattern of infrasound in the sea. Using a standing-wave acoustic tube, we have studied the sensitivity of cod to infrasound down to 0.1 Hz by means of the cardiac conditioning technique. The threshold values, measured as particle acceleration, showed a steady decline towards lower frequencies below 10 Hz, reaching a value close to 10(-5)ms-2 at 0.1 Hz. The spectrum level at 0.1 Hz in the sea ranges between 120 and 180 dB (re 1 microPa), with corresponding particle accelerations from less than 10(-6) to more than 10(-4)ms-2. The sensitivity of cod is thus sufficient to detect the highest levels of ambient infrasound, and we put forward the hypothesis that fish may utilize information about the infrasound pattern in the sea for orientation during migration, probably in addition to an array of other sensory inputs.

Acoustic Stimulation↗
PubMed1989

[Biophysical foundations of the effect of cosmic radiation and accelerator radiation].

This book summaries the results of numerous studies, mainly by Soviet investigators, of the characteristics of radiation effects of high energy cosmic rays and of their simulation by heavy charged particle accelerators, and also of their biological effects. It contains the first systematic presentation of data on specific hadron effects. Facts are given showing the ability of these particles to cause profound local damage in tissues and organs. There is evidence that these particles should be considered one of the main factors limiting the duration of space flights. In the book a generalized kinetic model of radiation-induced cellular damage also is presented. This model allows an explanations of the observed changes in dose related survival with increasing LET and dose-rate, based on microdosimetric conceptions.

Animals↗