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PubMed1976

Microdosimetric structure of heavy ion tracks in tissue.

Energy dissipation in tracks of high energy heavy ions in tissue shows a lateral spread of several to many microns depending on the energy of the primary particle. Complete dosimetric characterization, therefore, requires in addition to the Linear Energy Transfer (LET) information on the radial energy distribution. The theory of track structure distinguishes two regions: core and penumbra. The core is a narrow central zone with a radius in tissue far below 1 micron where energy deposition occurs mainly in processes of excitation and electron plasma oscillation. According to the Equipartition Principle, half of the total energy dissipation accrues in this manner. The penumbra is a peripheral zone enveloping the core where energy deposition occurs mainly in ionization events by energetic secondary electrons released by the primary particle in the center of the core traveling at rather high speed thus spreading laterally. The extension of the penumbra depends in a complex manner on the maximum transferable energy to electrons which in turn depends on the speed of the primary particle. Local energy density in the penumbra decreases with the square of increasing radius. It therefore amounts only to a very small fraction of the core density already a few microns away from the center. In general terms, track structure can be described as exhibiting a core of enormous energy density with lateral dimensions remaining entirely on the submicroscopic level surrounded by a penumbra where energy density drops precipitously to very small levels. The relationships are illustrated with micrographs of different sections of a heavy particle track in nuclear emulsion and their counterpart graphical plots.

Elementary Particles↗
PubMed1978

A heavy particle comparative study. Part IV: acute and late reactions.

The results of a comparative study of heavy particles of interest in radiotherapy are reported in four parts. In this Part IV, early skin reactions and late reactions (foot deformity) in mice for various heavy particles are reported. For heavy charged particles, the exposures were made at the entrance region (plateau) and centre of the peak (10 cm wide peaks). For 60Co gamma rays and fast neutrons (50 MeV D leads to Be), the exposures were made at the peak of the depth-dose curve. The time-course of development of skin reaction and subsequent healing after exposure to heavy ions or 60Co gamma rays were remarkably similar, suggesting that skin damage and subsequent epithelial repopulation after exposure to heavy ions are not different from 60Co gamma rays. When the Bragg peaks were broadened to 10 cm, the RBE at the peak, compared with the entrance region, was significantly higher for carbon ions but nearly the same or even lower for neon and argon ions because of saturation effects at high LET. The RBE for fast neutrons was comparable to that at the peak for carbon ions. The correlation between early skin reaction and foot deformity remained the same for all particles.

Animals↗
PubMed1979

Radiobiological effects and dose-LET spectra.

To advance our knowledge about radiobiological cell effects typical different cell reactions must be discriminated and studied individually. Today the 2-component theory which distinguishes between repairable beta-reactions and nonrepairable alpha-reactions, is the first step on this road. Such specialized investigations give a more detailed and clearer picture of the cell reactions than the usual RBE comparisons carried out with different radiation types. This is especially important for clinical radiotherapy where it is essential to increase the selectivity between reactions on normal and tumor cells. alpha-values for different types of radiation are communicated.

Alpha Particles↗
PubMed1983

[Cancer therapy using particle radiation].

Radiation therapy, which has significantly been on progressed by introduction of high energy X-ray and gamma-ray machines, is reaching to a turning point in order to improve further the results of the treatment. The treatment with particle radiations, characterized by either the high energy transfer to the surrounding tissues or the excellent dose distributions, i.e. Bragg peak, are in clinical trials. The results up to date show that the locally advanced, and radioresistant cancers have been more successfully controlled by applying fast neutrons than use of x-rays and that the damage to the normal tissues was less in the proton therapy compared with the conventional radiations. It is suggested from this clinical trial that the effect of particle radiations be more enhanced when the heavy ions, i.e., Neon ions and Silicon ions, become available.

Elementary Particles↗
PubMed1985

Particle radiation therapy.

Current interest in attempting to identify any therapeutic advantages of beams of heavy particles (heavier than electrons) over photons is based on differences in physical absorption and radiobiologic interactions. The article discusses: dose distributions in tissue, which are markedly different for particles than for high energy photons and so may be clinically advantageous for the former; differences in radiobiologic responses, which could lead to increased tumor cell killing and a possible increase in the therapeutic ratio for particles; clinical experience to date; directions for and impediments to future research.

Dose-Response Relationship, Radiation↗