Harald H. Rossi

Microdosimetry and Its Applications

From the contens: Microdosimetric Quantities and Their Moments.- Interaction of Radiation with Matter.- Experimental Microdosimetry.- Theoretical Microdosimetry.- Applications of Microdosimetry in Biology.- Other Applications.

A device for the measurement of dose as a function of specific ionization.

The physical parameters influencing the biological effect of ionizing radiation are the energy delivered to the tissues affected and the ion density along the paths of the charged particles producing the ions. Variations of the latter quantity are believed to be responsible for differences in relative biological effectiveness (R.B.E.). Zirkle has suggested the use of the concept of “linear energy transfer” (L.E.T.) in tissue. This is more fundamental than specific ionization in a gas, but the latter, which may be measured much more readily, may be presumed to be proportional to the former within about 10 per cent in most cases. At present there are several methods by which the total energy imparted to tissue by ionizing radiations can be determined. In this laboratory, tissue-equivalent ionization chambers (1) have been developed on the basis of the Bragg-Gray principle. Employing these chambers, one can obtain a measure of the total energy delivered per gram of tissue by particles of any specific ionizat...

Mutations induced in Tradescantia by small doses of X-rays and neutrons - Analysis of dose-response curves.

Dose-response curves for pink somatic mutations in Tradescantia stamen hairs were analyzed after neutron and x-ray irradiation with doses ranging from a fraction of a rad to the region of saturation. The dose-effect relation for neutrons indicates a linear dependence from 0.01 to 8 rads; between 0.25 and 5 rads a linear dependence is indicated for x-rays also. As a consequence the relative biological effectiveness reaches a constant value (about 50) at low doses. The observations are in good agreement with the predictions of the theory of dual radiation action and support its interpretation of the effects of radiation on higher organisms. The doubling dose of x-rays was found to be nearly I rad.

RBE AND THE PRIMARY MECHANISM OF RADIATION ACTION.

The dependence of RBE on dose appears to follow a simple relation for a variety of effects on higher organisms and for a broad range of doses. The data indicate that the biological effects are due to primary lesions that may be produced by one or two high LET particles but require the action of at least two electrons when electromagnetic radiation is applied. The interaction distance exceeds 1 μm.

The synergistic effects of different radiations.

Theoretical expressions, based on the Theory of Dual Radiation Action, are derived to calculate the effects of mixed radiation exposures on survival distributions. Temporal effects (such as recovery from sublethal injury) are explicitly included in the calculations. The results indicate the synergistic effect of sequential exposures due to the interaction between sublesions produced by the different types of radiation.

Specification of Radiation Quality

Radiation quality has been commonly expressed in terms of the LET of the ionizing particles that deliver the absorbed dose. The detuiled mechanism of energy loss of charged particles is such that there is a very complex relation between LET and the energy deposited in some small region of the irradiated tissue. The parameter Y is defined as the energy imparted to a small sphere divided by the sphere diameter. Representation of the dose in Y for a range of diameters yields information on the spatial distribution of energy, as well as on the local dose and the frequency with which such a dose is delivered. lt is believed that this representation may prove useful in fundamental radiobiological and radiochemical studies. (auth)

RBE as a function of neutron energy. I. Experimental observations

The survival of Chinese hamster cells in culture was used as a test system to determine the RBE of neutrons over a wide energy range. The Radiological Research Accelerator Facility (RARAF) at Brookhaven National Laboratory was used for experiments involving nine neutron energies between 110 keV and 15 MeV; for all but the lowest energy the beams were essentially monoenergetic. Additional experiments were performed with high energy cyclotron-produced neutrons at the Naval Research Laboratory, Washington, D. C., and at the Texas A&M Variable Energy Cyclotron (TAMVEC). In both cases broad neutron energy spectra were involved. In each experiment, survival curves were obtained for one neutron energy and compared with 250 kVp X rays, using cells from the same suspension and common controls. In this way a detailed study was made of the relation between RBE and neutron absorbed dose for each neutron energy. At any given cell survival level, RBE varies with neutron energy. Neutrons at 350 keV are biologically the ...

Radiation carcinogenesis at low doses

An analysis of experimental findings indicates that the induction of a manmmary neoplasm in the Sprague-Dawley rat is dependent on the action of radiation on more than one cell. Although a linear relation between incidence and x-ray dose might be consistent with available data, such a relation would be fortuitous and linear extrapolation to lower doses is unjustified.

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.

Dose-dependence of fast neutron RBE for lens opacification in mice.

Opacification of the optic lens in mice has been evaluated after exposure to the following radiations and doses: 250 kVp x-rays, 4.5-1,000 rads; 14 MeV neutrons, 0.5-60 rads; 1.8 MeV neutrons, 1-36...