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Results for “Linear Energy Transfer”

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At least 109 records · Page 6Linked to original sources
PubMed1989

Radiation-induced cell death by chromatin loss. A model to explain the shape of low-linear-energy-transfer cell survival curves.

A model is proposed which relates reproductive death of cells caused by radiation to loss of chromatin at cell division. This loss of chromatin can occur through chromosomal deletions or through the formation of asymmetrical chromosomal exchanges. It is proposed that smaller doses of radiation produce fewer chromatin breaks, which are more likely to be accurately repaired, compared with larger doses. Consequently, smaller doses of radiation are less efficient in causing cell death, leading to a shoulder on the cell survival curve. Experimental evidence supports this model, and the fit between the derived formula and experimental cell survival curves is good. The derived formula approximates to the linear-quadratic equation at low doses of radiation.

Cell Division↗
PubMed1993

The linear energy transfer dependence of excited singlet-state lifetimes of hydrocarbon liquids exposed to X rays.

The absorption of X rays in liquids provides low-energy electrons in the energy range 2 to 20 keV when synchrotron radiation is used as the X ray source. Such low-energy electrons have short ranges and produce a dense track of ionization where dE/dx = 10(7) to 10(8) eV/cm. Fluorescent molecules provide a sensitive probe of the early-time structure of such tracks. From the extent of quenching of excited states and the consequent decrease in fluorescence lifetimes, the concentration of free radicals in the track can be inferred. Experiments done with the hydrocarbons cis-decalin and dodecane demonstrate this effect. In both hydrocarbons, the lifetimes (tau) are significantly smaller with excitation by X rays than with UV radiation, and tau-1 increases linearly with dE/dx.

Alkanes↗
PubMed1993

Induction of sister chromatid exchange as a function of charged-particle linear energy transfer.

Frequencies of sister chromatid exchanges (SCEs) were evaluated in chromosome spreads of CHO-AA8 cells at the second mitosis after irradiation with charged particles of 10, 40, 80, and 120 keV/microns. At each LET there was a dose-dependent increase in the frequency of SCEs. In contrast to the majority of end points where relative biological effectiveness increases as LET increases up to an optimum and then declines, it was found that the most biologically effective particles were protons at 10 keV/microns, followed by deuterons at 40 keV/microns, then alpha particles at 80 and 120 keV/microns. Nuclear cross-sectional areas of these cells were log-normally distributed with a mean of 77 microns 2. When induced SCEs per chromosome were related to charged particles per cell nucleus (down to a mean of 0.5 particles per nucleus), results at low fluences favored a linear relationship between SCEs and particles which was relatively independent of LET. These observations are not compatible with the origin of radiation-induced SCEs being DNA double-strand breaks and favor the notion that they may be consistent with DNA single-strand breaks.

Alpha Particles↗
PubMed1979

Dependence of the nucleoside effect on linear energy transfer.

L929 cells were irradiated by cyclotron-produced neutrons and by 14.8 MeV monoenergetic neutrons. For comparison cells were also irradiated by 60Co gamma rays. Following irradiation cells were treated by an equimolar solution of deoxyribonucleosides, and the effect on cell survival measured. Results show that nucleoside treatment was efficient after low-LET irradiation: gamma ray survival curves were altered by deoxyribonucleosides in terms of significantly increased extrapolation numbers only, but without Do change. Cells irradiated by neutrons from either of the two sources did not respond to nucleoside treatment, and consequently their survival curves remained unaltered. These results show that the nucleoside effect does occur after low-LET irradiation, but apparently not following high-LET irradiation. Since deoxyribonucleosides as well as other cell breakdown products are released in irradiated and necrotic tumours due to massive cell destruction, such a nucleoside effect could possibly enhance the cell survival and thus effect the result of radiotherapy. Absence of the nucleoside effect in case of high-LET irradiation may therefore be an additional potential gain from neutrons in radiotherapy.

Animals↗
PubMed1986

Thermoluminescence of 7LiF in therapeutic high linear energy transfer (LET) charged-particle beams.

The thermoluminescence of the 200 and 260 degrees C peaks of 7LiF has been measured and compared with off-axis dose and depth-dose distributions for three therapeutic high-LET beams: negative pions, helium ions and neon ions. The methods of analysis consisted of both a single-peak analysis and the dual-peak analysis methods of Hogstrom and Irifune and Hoffmann et al. The results indicate that 7LiF, analysed by the dual-peak analysis methods, is potentially useful for extracting total dose, high-LET dose, and beam quality of helium-ion and negative-pion beams. For the higher-LET neon beam, differences in sensitivity between the 200 and 260 degrees C peaks of 7LiF were found to be independent of variations in LET within the beam; consequently, only the single-peak analysis method is applicable in which case the dosemeter at best can only estimate total dose.

Fluorides↗
PubMed2006

High-linear energy transfer irradiation targeted to skeletal metastases by the alpha-emitter 223Ra: adjuvant or alternative to conventional modalities?

The bone-seeking, alpha-particle-emitting radiopharmaceutical Alpharadin, 223RaCl2 (half-life=11.4 days), is under clinical development as a novel treatment for skeletal metastases from breast and prostate cancer. This article summarizes the current status of preclinical and clinical research on 223RaCl2. Potential advantages of 223Ra to that of external beam irradiation and registered beta-emitting bone seekers are discussed. Published data of 223Ra dosimetry in mice and a therapeutic study in a skeletal metastases model in nude rats have indicated significant therapeutic potential of bone-seeking alpha-emitters. This article provides short-term and long-term results from the first clinical single dosage trial. We also present data from a repeated dosage study of five consecutive injections of 50 kBq/kg body weight, once every 3rd week, or two injections of 125 kBq/kg body weight, 6 weeks apart. Furthermore, interim results are described for a randomized phase 2 trial involving 64 patients with hormone-refractory prostate cancer and painful skeletal metastases who received four monthly injections of 223Ra or saline as an adjuvant to external beam radiotherapy. Lastly, we present preliminary dose estimates for 223Ra in humans. Results indicate that repeated dosing is feasible and toxicity is low, and that opportunities are available for combined treatment strategies.

Alpha Particles↗
PubMed2003

Boron neutron capture therapy: cellular targeting of high linear energy transfer radiation.

Boron neutron capture therapy (BNCT) is based on the preferential targeting of tumor cells with (10)B and subsequent activation with thermal neutrons to produce a highly localized radiation. In theory, it is possible to selectively irradiate a tumor and the associated infiltrating tumor cells with large single doses of high-LET radiation while sparing the adjacent normal tissues. The mixture of high- and low-LET dose components created in tissue during neutron irradiation complicates the radiobiology of BNCT. Much of the complexity has been unravelled through a combination of preclinical experimentation and clinical dose escalation experience. Over 350 patients have been treated in a number of different facilities worldwide. The accumulated clinical experience has demonstrated that BNCT can be delivered safely but is still defining the limits of normal brain tolerance. Several independent BNCT clinical protocols have demonstrated that BNCT can produce median survivals in patients with glioblastoma that appear to be equivalent to conventional photon therapy. This review describes the individual components and methodologies required for effect BNCT: the boron delivery agents; the analytical techniques; the neutron beams; the dosimetry and radiation biology measurements; and how these components have been integrated into a series of clinical studies. The single greatest weakness of BNCT at the present time is non-uniform delivery of boron into all tumor cells. Future improvements in BNCT effectiveness will come from improved boron delivery agents, improved boron administration protocols, or through combination of BNCT with other modalities.

Animals↗
PubMedDate not supplied

[Modeling viability of mammalian cells exposed to ionizing radiation with different linear energy transfer].

A mathematical model of the survival of mammalian cells exposed to ionizing radiation is proposed, which takes into account nonuniform radiosensitivity of different regions of DNA. The model is based on the assumption that the double-strand breaks of the anchor DNA, induced either directly by irradiation or by enzymes, play a key role in the lethal radiation effect. The model survival curves are in good agreement with experimental curves measured in different laboratories.

Animals↗