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Biomedical subjects

H H Rossi

Publications and source records attributed to H H Rossi.

At least 37 records · Page 2Linked to original sources
PubMed1991

The radiobiological significance of spatial and temporal distribution of energy absorbed from ionizing radiations.

The cells of higher organisms respond in a non-linear fashion to the energy absorbed from ionizing radiation. However, there appears to be no indication of a dependence that is of a higher power than the square of the absorbed energy. This relatively simple alternative permits operational definitions of two types of injuries, termed lesions and sublesions, and a basic description in terms of dual radiation action. There are, however, various complicating factors and uncertainties. Further progress requires the development of a modified microdosimetry that incorporates energy transport, a more complete treatment of saturation and especially a specific identification of what is probably damage to DNA.

Animals↗
PubMed1990

A generalized definition of dosimetric quantities.

The current definitions of microdosimetric and dosimetric quantities use the notion of 'ionizing radiation'. However, this notion is not rigorously defined, and its definition would require the somewhat arbitrary choice of specified energy cut-off values for different types of particles. Instead of choosing fixed cut-off values one can extend the system of definitions by admitting the free selection of a category of types and energies of particles that are taken to be part of the field. In this way one extends the system of dosimetric quantities. Kerma and absorbed dose appear then as special cases of a more general dosimetric quantity, and an analogue to kerma can be obtained for charged particle fields; it is termed cema. A modification that is suitable for electron fields is termed reduced cema.

Radiation Dosage↗
PubMed1989

Microdosimetric measurements and the variance-covariance method. Some experimental experience.

Systematic and statistical uncertainties in the variance-covariance method have been investigated. Two spherical wall-less detectors have been used to determine the dose mean lineal energy (yD) in a neutron beam of 5.7 MeV produced by a Van de Graaff accelerator. It is shown that certain systematic uncertainties influenced the mean yD of the two detectors much less than yD from only one of them. A statistical uncertainty of 6% (95% confidence level) was achieved if yD was calculated from 2000 measurements. In this particular experiment insufficient shieldings of the preamplifiers positioned in the beam turned out to limit the possibility to measure below 20 nm.

Analysis of Variance↗
PubMed1989

Estimation of the quality factor on the basis of multi-event microdosimetric distributions.

The measurement of microdosimetric distributions for the purpose of estimating the quality factor, Q, may be encumbered in pulsed radiation fields--as produced, for instance, by accelerators with low duty cycle--because of a signal pile-up. We propose a method of estimating Q from the first several moments of multi-event distributions. In addition to overcoming the high dose-rate problems, the measurement of such distributions can be performed in significantly smaller volumes than conventional microdosimetry, thus raising the possibility of reducing the site diameter (presently 1 micron) for which y in the function Q(y) is specified.

Radiation Dosage↗
PubMed1989

A multi-element proportional counter for radiation protection measurements.

A detector incorporating about 300 individual counting volumes is described, and the results of performance tests are reported. The device can be employed for a direct measurement of the dose equivalent in an unspecified radiation field on the basis of the lineal energy spectrum in 1-micron diameter tissue regions. It is substantially smaller than a conventional tissue equivalent proportional counter yielding the same counting rate and may be useful for measurements in phantoms.

Radiometry↗
PubMed1988

The biophysical stage of radiation carcinogenesis.

The dependence of the induction of cancer on the absorbed dose of ionizing radiations has been specified in terms of increasing complexity. The first notion of simple proportionality (the "linear hypothesis") is now frequently replaced with a dependence of both the first and second powers of the dose (the "linear-quadratic model"), which implies proportionality at low doses only. Microdosimetric considerations, in particular the theory of dual radiation action, would be in accord with this relation if tumors were to arise from single cells as the result of a transformation that is autonomous (i.e., depends only on the radiation received by the cell). In this case, it must be expected that the linear portion of the dose-effect curve is dose rate independent, but that the quadratic component may decrease with decreasing dose rate because of repair during the interval between two events (energy depositions by individual particles). Various data appeared to be in agreement with this picture. However, it was shown some time ago that the dose-incidence relation of some neoplasms indicates a non-autonomous response because of departure from a linear dependence when the mean number of events in cells is much less than one in neutron irradiations. Another discrepancy is the repeated observation that reduction of dose rate, while resulting in the expected lessening of the effectiveness of low-LET radiation, increases the effectiveness of neutrons (especially in the case of oncogenic cell transformation). As will be shown, it is possible to account for this phenomenon, although at this point the limitations of the available data make the explanation semi-quantitative and therefore still somewhat hypothetical. However, it should be noted that it does not even require a nonautonomous response and thus is at least an example of the complexities that can arise in the earliest (biophysical) stage of radiation carcinogenesis.

Animals↗
PubMed1988

Microdosimetry near the trajectory of high-energy heavy ions.

Single-event energy distributions were measured in a 1.3-micron-diameter site as a function of radial distance from the trajectory of high-energy iron ions having an energy of about 600 MeV/amu. It was found that beyond distances of a few micrometers the average lineal energy of the (mostly single) secondary electrons (delta rays) is of the order of 3 keV/micron. This is similar to the value found in a medium irradiated by 170-keV photons. The frequency-mean specific energy for delta rays occurring at large distances from the path of the primary ion exceeds the calculated (radial) absorbed dose by two orders of magnitude.

Ions↗
PubMed1988

On the application of microdosimetry to radiobiology.

The pertinence of proportional counter microdosimetry to radiobiology rests on the idea of the site model; in view of the current emphasis on formalisms based on the distance model, it would appear that the role of experimental microdosimetry as a predictive tool is compromised. In this paper we challenge this opinion. It is shown that, to the extent that the site model is not only limited to convex sites of simple geometry, (a) the site model and the distance model become only complementary aspects (i.e., two possible interpretations) of the same formalism, and current biophysical theory is not equipped to discriminate, based on experimental evidence, between the two; (b) proportional counter microdosimetry retains its validity; and (c) for any cellular system [characterized by a function gamma(chi)] the ratio alpha/beta between the linear and quadratic components of the dose-response function can be calculated as a weighted sum of dose-averaged specific energies measured in a series of spherical sites (of different dimensions). An algorithm is provided for calculating the weighting factors.

Mathematics↗
PubMed1987

Inactivation of synchronized mammalian cells with low-energy X rays--results and significance.

Results for inactivation of hydroxyurea-synchronized V-79 cells by ultrasoft aluminum characteristic X rays of energy 1.5 keV are presented. Limiting RBEs at low doses, relative to 137Cs gamma rays, of 1.8 and 6.4 are, respectively, found for cells at the G1/S and late S stages of the cell cycle. The late-S data are analyzed in the light of previous experiments carried out under similar conditions, also designed to probe the effects of energy deposition in nanometer-sized sites, in which cells were irradiated with correlated pairs of ions. Within the framework of the theory of dual radiation action, the results for ultrasoft X rays and gamma rays can be deduced solely from track simulations and the results of the high-LET molecular ion experiment.

Animals↗
PubMed1985

Lauriston S. Taylor Lecture. Limitation and assessment in radiation protection.

Protection against ionizing radiation can follow two fundamentally different approaches. In limitation, the maximum permissible dose equivalent is selected on the basis of worst-case assumptions on the shape of dose-effect curves and the influence of other factors (dose distribution, relative biologic effectiveness, etc.). This system has the restricted aim of ensuring that radiation exposure results in risks below stipulated levels. In assessment, the functional relation and the numeric values required for risk estimation are postulated. This permits statements of the absolute values of risks, not only for the maximum permissible dose equivalent but also for any lesser dose equivalents. The principal concept underlying the assessment system is that of incoherence: lack of interdependence between the effects of dose increments and lack of interdependence between the effects on the constituent cells and organs of the body. The notion of incoherence and the choices of numeric values of risks are subject to substantial doubts. They must nevertheless be adopted when risk estimation cannot be avoided.

Animals↗
PubMed1985

Dual radiation action and the initial slope of survival curves.

The concepts and tools of the Theory of Dual Radiation Action (e.g., proximity functions and gamma distributions) are outlined, and their connection to single-event cell inactivation is exemplified by an analysis and interpretation of the cross-section data obtained by Todd. It is shown that the biological effect of individual charged particles is dominated by the combined action of a few delta rays.

Animals↗