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Biomedical subjects

D Harder

Publications and source records attributed to D Harder.

At least 91 records · Page 5Linked to original sources
PubMed1980

Absence of fractionation, protraction, radiation quality, and radical scavenger effects on radiation-induced interphase death of human G0 lymphocytes in vitro.

In vitro interphase death of human peripheral blood lymphocytes, measured by shortening of the mean lifetime of small G0 lymphocytes, was studied with 150 kV and 10 kV X-rays. No effect of radiation quality, of fractionation and of protraction was observed. The possibility of protection by L-cysteine and DMSO was tested in cells irradiated with 150 kV X-rays, but no protection effect with respect to cell survival could be demonstrated. Non-DNA radiation-sensitive site(s), possibly the cell membrane, appear to be responsible for interphase death.

Cell Membrane↗
PubMed1978

Systematic optimization of the double-scatterer system for electron beam field-flattening.

The scattering foil widely used for field flattening in electron therapy produces a distortion of the electron spectrum which significantly reduces the slope of the descending part of the depth dose curve. It is already known that this effect can be drastically reduced by replacing the scattering foil by a two-foil scatterer. The second foil, fit with a radial thickness profile, acts as a compensator, attenuating the central part and enhancing the peripheral part of the beam by electron scattering. Calculations of the optimal foil combinations and radial thickness profiles are presented and numerical values of smooth (Gaussian) and three-step profiles for various field sizes are provided. The results are applicable to a variety of electron energies and scattering foil materials.

Electrons↗
PubMed1978

[Calculation of the dose distribution of high-energy electrons within and behind tissue inhomogeneities of any width. II. Influence of multiple scattering (author's transl)].

The algorithn proposed in 1976 to allow for the influences of tissue inhomogeneities in electron beam dose distributions has been improved. A factor adopted from Sternheimer corrects for differences in lateral displacement by multiple scattering within the inhomogeneity resp. the equivalent layer of the homogeneous medium. The algorithm has been tested by direct comparison with Monte Carlo computations for the example of cylindrical cavities in carbon at Eo=10 MeV and resulted in a very close approximation.

Carbon↗
PubMed1977

The RBE of 30 kV X-rays for the induction of dicentric chromosomes in human lymphocytes.

The frequency of dicentric chromosomes induced by the irradiation of human lymphocytes in Go phase was determined with hard (150 kV) and soft (30 kV) X-rays. When a linear-quadratic dose-effect relation was used to fit the experimental data, a significant linear contribution was found for 30 kV X-rays. The RBE of 30 kV compared with 150 kV X-rays approaches the value 3 at a 30 kV X-rays dose of 20 rad and decreases with increasing dose. From the results it may be concluded that chromatids with primary breaks, undergoing second order reactions and thus forming dicentric chromosomes, are produced by traversals of low-energy electrons through chromatin material.

Adult↗
PubMed1976

[Calculation of dose distribution of fast electrons within and behind tissue inhomogeneities of any width].

A new algorithm allowing for the effects of tissue inhomogeneities on dose distributions of high-energy electrons is presented for the purposes of treatment planning computations. Starting from the electron dose distribution for homogeneous tissue the doses contributed by the partial beam hitting the tissue inhomogeneity are substituted by those arising from a partial beam which was alterated by stopping, scattering and changed distances in the inhomogeneity. Since actual data for partial beams of limited cross-section are used and the scatter contributions from the rest of the total beam into and behind the inhomogeneity remain unchanged, good approximation compared to measured values is achieved.

Electrons↗
PubMed1976

[The new radiologic units of measurement gray and becqerel (author's transl)].

The general conference on weights and measures in June 1975 introduced the new names of units, the Gray (for ionizing radiations) and the Becqerel (for activity of a radioactive substance), on an international level. The reasons for this change--the units hitherto valid are the Rad and the Curie--and the international efforts at durability of the new regulations are reported.

Health Physics↗