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At least 649 records · Page 36Linked to original sources
PubMed1981

Muon dose distribution from a decaying pencil beam of pions.

Increased interest in the use of negative pion beams for radiotherapy has led to a requirement for accurate knowledge of the extent and effect of beam contamination. Contaminating muons from the decay of pions upstream of the irradiation position cannot be easily identified by time-of-flight or range measurement techniques. A calculation of the stopping and dose distributions of these muons was performed. A monoenergetic pencil beam of 180 MeV/c pions, normally incident onto a semi-infinite water slab, was assumed to decay into muons over the one metre distance upstream of the water and in the water. Dose from the subsequent decay of muons to electrons was included. Contour maps of the stopping and dose distributions are presented as well as the stopping and depth-dose distributions for an infinite beam. The calculation clearly illustrates that muons from the decay of monoenergetic pions do not have a unique momentum and range, but rather include a wide spectrum of ranges and momenta. Since a muon dose contribution of 16% has been calculated at a depth of 8 cm, these muons could result in unexpected nonuniformities in dose in a clinical pion irradiation if they are ignored in pion treatment planning.

Elementary Particles↗
PubMed1981

Dose calculations for 123I, 124I, 125I and 131I in the thyroid gland of the mouse, rat and man and comparison with thyroid function for mice and rats.

To assess the radiotoxicity of various iodine isotopes to the thyroid gland, refined dosimetric calculations of the average dose rate distribution and total absorbed dose were performed using Monte Carlo Procedures applied on a microscopic scale to the electrons emitted by the isotopes and on a macroscopic scale to the photons. The calculated dose rates depended strongly on the average follicle radius, surrounding cell layer thickness and thyroid mass and the total absorbed doses were calculated from them for the mouse, rat and man as a function of the age at the time of administration. The thyroid function of mice and rats after injection of various isotopes, as measured by several authors, was compared with the calculated average absorbed doses in the thyroid and in different parts of the cell layers. Changes in cell layer thickness due to diet were taken into account. The calculated average absorbed dose in the outermost half of the cell layer was found to be better as a prediction of thyroid damage for all species mentioned. The improvement in prediction was obvious for mice and rats, but less important for adult man.

Animals↗
PubMed1982

The design and construction of a realistic thorax phantom for in vivo measurements of low-energy photon emitters.

Calibration of detector systems for the in vivo measurement of transuranic radionuclides is notoriously difficult due to the low energies and intensities of the photon emissions and their severe attenuation within the tissues of the body. A realistic chest phantom has been designed and constructed to provide calibration data to relate detector responses to lung contents of radionuclides; the phantom incorporates a human thoracic cage and tissue substitutes that have been carefully selected to reproduce the scattering and absorption coefficients of muscle and lung tissue. The measured attenuation coefficients of the substitutes are compared with values calculated for the tissues of interest. Preliminary calibration data obtained from this phantom are presented and the uses and limitations of this calibration procedure are discussed.

Calibration↗
PubMed1982

Corrections for scattered photons in free-air ionisation chambers.

Although most recent interest and development in radiation dosimetry has been centered on higher energy radiations, calibrations of conventional x-ray machines for radiotherapy are still based on free-air ionisation chamber measurements. Such measurements require a correction for ionisation produced by secondary photons scattered out of the primary beam, and although the correction is relatively small (generally less than 1%) the data for deriving it are neither as complete or satisfactory as might be wished. This paper describes the derivation of theoretical expressions which allow the calculation of corrections, and compares calculated values with experimental results. It is apparent from the study that in determining the photon gain correction, account should be taken not only of the chamber geometry but also of photon scattering from the wall materials and, for higher energy beams in particular, of contributions from diaphragm scatter and possibly stray radiation penetration of the chamber.

Elementary Particles↗
PubMed1983

A lyoluminescent tissue-equivalent dosemeter for pion therapy beams.

The light emitted when pion irradiated glucose is dissolved in luminol solution has been found to be proportional to the pion beam depth dose distribution in water as determined by a TE ionisation chamber. The lyoluminescence of glucose overlaps very closely with the response profile of the ionisation chamber to the 170 MeV/c pi--mesons giving a Bragg peak to plateau ratio of 3:1. In comparison, the thermoluminescence response of LiF (TLD-700) to pions has been found to deviate significantly from this ratio. The close tissue equivalence of glucose, non-toxicity and its excellent lyoluminescent retention properties are important advantages over currently used dosemeters in clinical pion therapy, especially when direct in vivo measurements are considered. Pion doses ranging between 0.5 Gy (50 rad) and 30 Gy (3000 rad) were measured with an accuracy +/- 5% and reproducibility 3-5%.

Elementary Particles↗
PubMed1985

A measurement of the local energy deposition by antiprotons coming to rest in tissue-like material.

The measurement of the energy deposited in tissue-equivalent plastic as a beam of low-energy antiprotons slows down is described. The resulting depth-dose curve is presented and compared with that of protons measured under similar conditions. These curves indicate that the ratio of the dose in the antiproton stopping peak to that in the plateau region is about twice that found for protons. Analysis of the data shows that out of the 2 GeV available in an antiproton annihilation, on average less than 30 MeV is deposited close to the site of the interaction. This leads to the conclusion that antiprotons are unlikely to offer any marked advantage over other radiations for radiotherapeutic applications of the future.

Animals↗
PubMed1987

Pionic carbon/oxygen capture ratios in blood and muscle tissue of pig.

The pionic carbon/oxygen capture ratio for the blood and muscle tissue of a pig was measured using an intrinsic Ge detector in order to investigate possible explanations for an enhanced lesion observed in the autopsy of pion-irradiated patients. Pure iron was also irradiated in order to determine the energies and intensities of pionic x-rays from iron. It was expected that some of them originated from haemoglobin and could be observed in the spectrum for a blood sample. TE plastic (Shonka A-150) and Lucite were also investigated for comparison with other work.

Animals↗
PubMed2001

Mechanical haemolysis in shock wave lithotripsy (SWL): I. Analysis of cell deformation due to SWL flow-fields.

This work analyses the interaction of red blood cells (RBCs) with shock-induced and bubble-induced flows in shock wave lithotripsy (SWL), and calculates, in vitro, the lytic effects of these two flows. A well known experimentally observed fact about RBC membranes is that the lipid bilayer disrupts when subjected to an areal strain (deltaA/A)c of 3%, and a corresponding, critical, isotropic tension, Tc, of 10 mN m(-1) (1 mN m(-1) = 1 dyne cm(-1)). RBCs suspended in a fluid medium tend to deform in accordance with the deformation of the surrounding fluid medium. The fluid flow-field is lytically effective if the membrane deformation exceeds the above threshold value. From kinematic analysis, motion of an elementary fluid particle can always be decomposed into a uniform translation, an extensional flow (e.g. -->uinfinity(x, y, z) = (k(t)x, -k(t)y, 0)) along three mutually perpendicular axes, and a rigid rotation of these axes. However, only an extensional flow causes deformation of a fluid particle, and consequently deforms the RBC membrane. In SWL, a fluid flow-field, induced by a non-uniform shock wave, as well as radial expansion/implosion of a bubble, has been hypothesized to cause lysis of cells. Both the above flow-fields constitute an unsteady, extensional flow, which exerts inertial as well as viscous forces on the RBC membrane. The transient inertial force (expressed as a tension, or force/length), is given by Tiner approximately rhor(c)3k/tau, where tau is a timescale of the transient flow and r(c) is a characteristic cell size. When the membrane is deformed due to inertial effects, membrane strain is given by deltaA/A approximately ktau. The transient viscous force is given by Tvisc approximately rho(nu/tau)1/2r(c)2k, where rho and nu are the fluid density and kinematic viscosity. For the non-uniform shock, the extensional flow exerts an inertial force, Tiner approximately 64 mN m(-1), for a duration of 3 ns, sufficient to induce pores in the RBC membrane. For a radial flow-field, induced by bubble expansion/implosion, the inertial forces are of a magnitude 100 mN m(-1), which last for a duration of 1 micros, sufficient to cause rupture. Bubble-induced radial flow is predicted to be lytically more effective than shock-induced flow in typical in vitro experimental conditions.

Biomechanical Phenomena↗
PubMed1994

Forward production of protons in relativistic 12C-nucleus collisions.

The production of protons in heavy ion collisions through the knockout mechanism (abrasion) is described using the Glauber model. The multiple knockouts from the projectile, including the inelastic collision series with the target, are considered using a closure approximation in treating energy conservation. Calculations for reactions of 12C projectiles with several targets at energies of 1 and 2A GeV arc compared to experiments. For large secondary proton momentum a strong dependence on the target mass is found and attributed to multiple scattering of the projectile knockouts.

Carbon↗