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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↗
PubMed2004

Radiotherapeutical innovations in pediatric solid tumors.

There have been considerable technical improvements in radiation therapy for the past two decades. In children affected with cancer, these have been likely overshadowed by concommittant major chemotherapy-based advances, and at least in part ignored and misused. This article outlines principles, technological requirements, and clinical applications of innovations that aim at improving ballistical selectivity (such as conformal, intensity modulation, stereotactic photons, charged particles, and intraoperative therapies), as well as at influencing tumors and normal tissues sensitivity to radiations (such as high LET particles, and altered fractionations).

Brachytherapy↗
PubMed2002

Model predictions and visualization of the particle flux on the surface of Mars.

Model calculations of the particle flux on the surface of Mars due to the Galactic Cosmic Rays (GCR) can provide guidance on radiobiological research and shielding design studies in support of Mars exploration science objectives. Particle flux calculations for protons, helium ions, and heavy ions are reported for solar minimum and solar maximum conditions. These flux calculations include a description of the altitude variations on the Martian surface using the data obtained by the Mars Global Surveyor (MGS) mission with its Mars Orbiter Laser Altimeter (MOLA) instrument. These particle flux calculations are then used to estimate the average particle hits per cell at various organ depths of a human body in a conceptual shelter vehicle. The estimated particle hits by protons for an average location at skin depth on the Martian surface are about 10 to 100 particle-hits/cell/year and the particle hits by heavy ions are estimated to be 0.001 to 0.01 particle-hits/cell/year.

Cosmic Radiation↗
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↗
PubMed1986

Delta excitations and shell-model information in heavy-ion, charge-exchange reactions.

We calculate total cross sections for coherent pion production using localized plane-wave approximations for the shell-structure of valence nucleons that are excited to delta particles in the intermediate state in the (12C, 12B) and (12C, 12N) charge-exchange, heavy-ion reactions. We find comparable agreement to projectile downshift data for 12C(12C, 12B)12N. Then we improve the formalism by replacing the localized plane wave bound states with harmonic oscillator states which are imbedded in a multipole expansion approach and calculate pion differential cross sections to test for the sensitivity of the spectra to the single-particle mass parameter.

Boron↗
PubMed1996

Secondary particle contribution to LET spectra on LDEF.

Four experiments utilizing passive detectors (P0006, P0004, A0015, M0004) were flown on LDEF to study the radiation environment. These experiments have been summarized in a companion paper (Benton et al., 1996). One of the experimental goals was to measure LET spectra at different locations and shielding depths with plastic nuclear track detectors (PNTD). It was found that the LET spectra extended well above the LET cutoff imposed by the geomagnetic field on GCR particle penetration into LEO. The high LET particles detected were mostly short-range (range < 2000 m), indicating that they were secondaries produced locally within the PNTD. The presence of these high LET particle fluences is important for the determination of dose equivalent because of the high Quality Factors (Q) involved. A relatively small fraction of particle fluence can contribute a large fraction of dose equivalent. Short-range, inelastic secondary particles produced by trapped protons in the South Atlantic Anomaly (SAA) were found to be a major contributor to the LET spectra above 100 keV/micrometer. The LET spectra were found to extend beyond the approximately 137 keV/micrometer relativistic GCR Fe peak to over 1000 keV/micrometer. The high LET tail of the LET spectra was measured in CR-39 and polycarbonate PNTDs using different techniques. GCR made a relatively modest contribution to the LET spectra as compared to the contributions from short-range secondary particles and stopping protons. LET spectra intercomparisons were made between LDEF measurements and exposures to 154 MeV accelerated proton beams. The similarities support the role of nuclear interactions by trapped protons as the major source of secondary particles in the PNTDs. Also techniques were employed to reduce the range cutoff for detection of the short-range secondaries to approximately 1 micrometer, so that essentially all secondary particles were included in the LET spectra. This has allowed a more realistic assessment of secondary contribution to dose equivalent. Comparisons of measured and calculated LET spectra have been made that demonstrate the need for more accurate modeling of secondary particles in radiation transport codes. Comparisons include preliminary calculations in which attempts have been made to include secondary particles.

Atlantic Ocean↗
PubMed2003

Analysis of dose-LET distribution in the human body irradiated by high energy hadrons.

For the purposes of radiological protection, it is important to analyse profiles of the particle field inside a human body irradiated by high energy hadrons, since they can produce a variety of secondary particles which play an important role in the energy deposition process, and characterise their radiation qualities. Therefore Monte Carlo calculations were performed to evaluate dose distributions in terms of the linear energy transfer of ionising particles (dose-LET distribution) using a newly developed particle transport code (Particle and Heavy Ion Transport code System, PHITS) for incidences of neutrons, protons and pions with energies from 100 MeV to 200 GeV. Based on these calculations, it was found that more than 80% and 90% of the total deposition energies are attributed to ionisation by particles with LET below 10 keV microm(-1) for the irradiations of neutrons and the charged particles, respectively.

Body Burden↗
PubMed2003

A new dynamical atmospheric ionizing radiation (AIR) model for epidemiological studies.

A new Atmospheric Ionizing Radiation (AIR) model is currently being developed for use in radiation dose evaluation in epidemiological studies targeted to atmospheric flight personnel such as civilian airlines crewmembers. The model will allow computing values for biologically relevant parameters, e.g. dose equivalent and effective dose, for individual flights from 1945. Each flight is described by its actual three dimensional flight profile, i.e. geographic coordinates and altitudes varying with time. Solar modulated primary particles are filtered with a new analytical fully angular dependent geomagnetic cut off rigidity model, as a function of latitude, longitude, arrival direction, altitude and time. The particle transport results have been obtained with a technique based on the three-dimensional Monte Carlo transport code FLUKA, with a special procedure to deal with HZE particles. Particle fluxes are transformed into dose-related quantities and then integrated all along the flight path to obtain the overall flight dose. Preliminary validations of the particle transport technique using data from the AIR Project ER-2 flight campaign of measurements are encouraging. Future efforts will deal with modeling of the effects of the aircraft structure as well as inclusion of solar particle events.

Aerospace Medicine↗