The significance of radiation-induced chromosome abnormalities in radiological protection.
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Chromosome Aberrations↗
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Mean excitation energies for stopping powers in various materials composed of elements hydrogen through argon.
The basic model of Lindhard and Scharff, known as the local plasma model, is utilized to study the effects of the chemical and physical state of the medium on its stopping power. Unlike previous work with the local plasma model, in which individual electron shifts in the plasma frequency were estimated empirically, the Pines correction derived for a degenerate Fermi gas is shown herein to provide a reasonable estimate even on the atomic scale. Thus, the model is moved to a completely theoretical base requiring no empirical adjustments, adjustments characteristics of past applications. The principal remaining error is in the overestimation of the low-energy absorption properties characteristic of the plasma model in the region of the atomic discrete spectrum, although higher energy phenomena are accurately represented and even excitation-to-ionization ratios are given with fair accuracy. Mean excitation energies for covalently bonded gases and solids, ionic gases and crystals, and metals are calculated using first-order models of the bonded states for which reasonable agreement with the recently evaluated data of Seltzer and Berger is obtained. Hence the methods described herein allow reasonable estimates of mean excitation energy for any physical-chemical combination of material media for stopping power applications.
Aluminum↗
Spatial distribution of effects of negative poins on cultured human cells.
Cultured human kidney T-1 cells were irradiated in flasks or on coverslips at different depths in a water phantom using the Los Alamos Meson Physics Facility Biomedical negative pion beam. Postirradiation colony formation and cell multiplication were assayed. Maximum cell inactivation occurred in the vicinity of maximum pion dose. Comparison of dose-survival curves with those found following x irradiation indicated RBE = 1.4 plus or minus 0.3 for colony formation and approximately 1.5 for growth delay. Delivery of 400 pion rads in four fractions resulted in higher survival than did delivery of 400 rads in a single fraction.
Cell Division↗
Initial comparative response of experimental tumors to peak pions and x rays.
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Adenocarcinoma↗
Microdosimetry of negative poins at LAMPF.
Lineal energy distributions and linear energy transfer (LET) spectra are being measured at the biomedical facility of the Los Alamos Scientific Laboratory for a negative pion beam having an initial momentum of 168 MeV/c. The results show that the fraction of the dose for lineal energies greater than 50 keV/mum is approximately 2% in the plateau and approximately 12% at the Bragg peak. Preliminary data indicate that the high lineal energy (and high LET) component increases significantly in the region slightly downstream from the peak.
Elementary Particles↗
Characteristics of a negative pion beam in a therapeutic application.
Lithium-drifted silicon detectors were used to investigate the components of the pion beam at the Los Alamos Meson Physics Facility. The components of the incoming beam are about 5% electrons, 10% muons, and 85% pions. Pulse spectra of the incoming beam and of the "stars" produced by the pions were obtained in a phantom. The analysis of the spectra into different LET components showing where pions are most effective is presented.
Electrons↗
Biological effects of the Los Alamos meson beam on cells in culture.
Preliminary measurements of the biological effects of negative pions on cells in culture are reported. Cell survival as a function of depth was obtained by using gelatin to suspend the cells. The results indicate that the effects are more pronounced at the peak portion of negative pions. Cell-survival curves were also obtained under oxygenated and hypoxic conditions. The biological effectiveness at the peak was found to be a factor of 2.0 higher than at the plateau. The oxygen enhancement ratio was 1.5 at the peak. No significant differences in biological effects were observed above 14 mm in the peak region.
Animals↗
Relative biological effectiveness of negative pi mesons for the immune response in mice.
Immunologically competent mouse spleen cells were exposed to negative pi mesons in the entrance plateau or at the peak of the dose distribution at a maximum dosage of 5 rads/min. or to 60Co gamma rays at 4.96 rads/min. Survival curves from cells irradiated in vitro but incubated in vivo yielded RBE values of 2.15 for the peak and 1.84 for the entrance plateau at a surviving fraction of 0.1. The dose-rate dependence of antibody-forming spleen cells for both 60Co gamma rays and the lot-LET components of the pion beam is discussed. The authors suggest that these RBE values constitute an upper limit for normal mammalian cells exposed to pions and tha the RBE with clinically useful dose rates may be significantly lower than those reported here.
Animals↗
Tissue chemical analysis with muonic x rays.
The stopped muon channel at the Clinton P. Anderson Meson Physics Facility was used as a source of muons for studying the elemental composition of tissue via muonic x rays. The x-ray spectra from several types of tissue were used to determine the amounts of carbon, nitrogen, and oxygen present. These determinations agree with the results of more conventional chemical analysis. Muonic x rays offer a noninvasive technique for determining the amounts of the more abundant elements in selected regions of the body.
Animals↗
Effects of negative pi mesons on mouse bone marrow cells.
Mouse bone marrow cells exposed in vitro to graded doses of negative pi mesons at 3.5-6.0 rads/min. gave Do values of 160 rads in the plateau (0.6 and 12.0 cm), and 130 rads in the peak (16.5 and 18.4 cm). Survival curve shoulders were narrow, with Dq values of 25 and 15 rads for plateau and peak positions. Gamma rays from 60Co at 4.5 rads/min. produced a curve with wider shoulder but steeper slope such that the RBE was essentially 1 for single doses between 100-400 rads.
Animals↗
Initial performance of the Stanford Medical pion generator.
A novel, cylindrical geometry, superconducting pion channel has been constructed at Stanford. It can simultaneously deliver up to 60 radially converging pion beams of the same mean momentum but with individually variable momentum spread (0.0-4.3%). Virtually no tuning of the pion beam is required Preliminary tests have demonstrated many of the performance characteristics which facilitate the treatment of selected human tumors.
Cold Temperature↗
Utilization of a high energy photon beam for whole body irradiation.
Use of a high energy linear accelerator (giving high dose rates) for whole body irradiation is recommended because (a) there is a shorter treatment time compared with other techniques using orthovoltage or 60Co irradiation; and (b) there is more comfort for the patient, who does not have to turn over to receive an acceptably uniform dose. Dosimetry indicates that the usual data is not applicable for such treatments given at large distances from the source. A method of dosage calculation at large distances was checked by using TLD dosimetry in a Rando phantom.
Elementary Particles↗
A comprehensive study of LiF TL response to high energy photons and electrons.
Effects of beam quality, cavity size, TLD state, and medium on the response of thermoluminescent dosimeters were studied. LiF TL-700 powder, extruded rods, and ribbons were irradiated with Co-60 gamma rays, 4, 6, 8, 33, and 45 -MV x rays, and 3, 5, 10, 15, 20, 25, 30, 35, 40, and 45-MeV electrons. Relative TL responses were assessed in water and Lucite, and the results compared. The results of this study were compared with those of previously published studies, and certain discrepancies resolved.
Cobalt Radioisotopes↗
Backscatter from high atomic number materials in high energy photon beams.
High atomic number materials in high-energy photon beams produce an increased radiation level on the side of the material towards the radiation source. This added radiation has been termed backscattered radiation, although it must also contain characteristic radiation from the scattering material. The magnitude and distribution of this radiation were investigated principally for the photon beam from an 8 MeV medical linear accelerator, and also for the beam from a 60Co teletherapy unit.
Alloys↗
Current status of clinical pion radiotherapy.
An RBE for acute skin reaction to peak pions, for a specific fractionation scheme, has been established at 1.40-1.44. The time of development of acute skin reactions varied in 2 patients with 30 metastatic skin nodules treated with doses varying from 1,175 to 1,951 peak pions and 2,350 to 3,901 rads of 100 kVp x rays. The reactions reached their peak approximately one week apart at all dose levels with both forms of radiation. No untoward effects have been seen in epidermis or subcutaneous tissues as late as 169 days after the start of treatment. All nodules disappeared and have not returned 169 days after treatment. There is a strong suggestion that the response of thick tumors is sensitive to the proportion of high LET radiation deposited at various levels in the tumor.
Dose-Response Relationship, Radiation↗
Effects of negative pi mesons on immune responses in mice.
Spleen cells from normal or preimmunized mice were exposed to graded doses of peak pions or 300-kVp x rays in vitro and then cultured in heavily irradiated mice to determine antibody production against sheep erythrocytes. The RBE for the primary antibody response was 1.46. Equal suppression of secondary responses was seen with both pions and x rays. When spleen cells were irradiated 1, 3, or 5 days after antigen injection, developing immune responses became less sensitive to pions than to x rays. Because T-cell activity (needed for the antibody response) is also implicated in tumor immunity, antitumor immune responses might not be more sensitive to pions than the response used; also, pions might not impair ongoing autochthonous immune responses more than conventional radiation modalities do.
Animals↗
Optimization of electrostatic imaging systems for minimum patient dose or minimum exposure in mammography.
The x-ray photon energies that give the highest signal-to-noise ratios per unit of exposure or average dose in mammography are significantly greater than those used in current film/screen systems. Optimum photon energies for detection of calcifications in a range of thicknesses of water and fat were calculated. Soft-tissue targets were also considered. Comparison of the theoretical results and those obtained experimentally with the Stanton mammography phantom indicate that operation at less than optimum photon energies is a major cause of inefficiency in film/screen mammography. On the other hand, electrostatic imaging systems, because of their processing flexibility, can operate at the optimum photon energy levels, thus minimizing either dose or exposure.
Elementary Particles↗
Myocardial imaging using emission computed tomography.
Single-photon emission computed tomography (ECT) was evaluated during myocardial studies in dogs. Acute anterior and posterior infarcts were imaged following injection of 99mTc-pyrophosphate or 201Tl. In most cases, tomographic delineation of infarct location and extent correlated with tissue section. The 99mTc images were far superior to the 201Tl images. ECT improves delineation of tracer within the myocardium.
Animals↗