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Biomedical subjects

M Lokajícek

Publications and source records attributed to M Lokajícek.

At least 19 recordsLinked to original sources
PubMed2001

Cell inactivation by ionizing particles and the shapes of survival curves.

Recent experiments concerning the survival of monolayer cells irradiated by different parts of ion Bragg peaks opened a way to a deeper mechanistic understanding of cell inactivation. A new theoretical formula for survival curves has been derived reflecting two basic phases of the given mechanism, i.e. energy transfer to a cell nucleus and subsequent biological effect (depending on the amount of imparted energy). The survival ratio for a given dose has been expressed as a function of inactivation probabilities of individual cells after different numbers of nucleus hits (a given amount of energy being transferred to a cell nucleus in each ion traversal). Having used the experimental data for V79 cells irradiated by protons, deuterons and helium ions in different parts of Bragg peaks preliminary values of these inactivation probabilities for individual cells at different LET values have been established.

Animals↗
PubMed2000

The role of oxygen in DNA damage by ionizing particles.

The actual role of oxygen in inactivation mechanism represents still an open problem, especially when Ewing (1998, Am. J. Clin. Oncol.21, 355-361) has shown that oxygen fixation hypothesis cannot be regarded as maintainable more and, on the other side, has argued that the oxygen effect can be hardly a simple consequence of greater reactivity of oxygen radicals. However, the role of oxygen in DSB formation may be more complicated even during the chemical phase of the radiobiological mechanism, as will be shown by computer simulation of the data concerning DSB number dependence on oxygen concentration (for different gas mixtures) and established experimentally by Blok and Loman in 1973 (Radiat. Res.9, 165-245) by irradiating DNA water solutions by gamma radiation.

Computer Simulation↗
PubMed1996

Perspectives of tumour radiotherapy in the Czech Republic and "Oncology 2000" Foundation.

The incidence of tumours has still an increasing tendency. A great effort is being devoted to prevention as well as to improving early diagnosis and treatment. It is the radiotherapy which seems to bring new treatment possibilities at the present. Its goal consists in destroying all tumour cells in the target volume while all normal cells being damaged unsubstantially only. That is being achieved with standard available means only with rather great difficulties. However, in the last time two radiotherapy methods have been developed which are based on the use of the so called hadrons (i.e. particles exhibiting strong mutual interactions) and come nearer to the mentioned ideal goal of any tumour therapy. The first method consists in the application of beams of charged hadrons having a suitable characteristic of energy transfer; the most energy being transferred to the matter in the end of hadron tracks. Thus, by a suitable choice of initial energy of beam particles this maximum may lie in a tumour volume, while all other tissues obtain a smaller dose, the difference being greater when a multiple-field technique is used. The other approach (neutron capture therapy-NCT) makes use of epithermal (or thermal) neutrons captured by special isotopes accumulated in tumour cells with the help of suitable chemical carriers. Both the methods are now being introduced into clinical use in many countries. The "Oncology 2000" Foundation was grounded to introduce these methods into clinical use also in the Czech Republic. It proceeds with activities started by an interdisciplinary group of specialists formed approximately 20 years ago and having prepared some necessary conditions. As to the NCT a corresponding facility is now being finished and clinical tests are expected to be started in 1997. The main attention is now devoted to building up an oncology center based on the use of hadron beams.

Czech Republic↗
PubMed1988

Mathematical models of cumulative effect and optimization of fractionation regimes.

Different (most known) mathematical models are shortly described and basic assumptions the individual models are based on are discussed and critically examined. Advantages and shortages of individual models are mentioned. A semiphenomenological model is then used to demonstrate some possibilities how to make use of the mathematical models in attempts of optimizing the fractionation approaches in individual cases.

Dose-Response Relationship, Radiation↗
PubMed1986

Modelling of DNA sedimentation profiles from irradiated eukaryotic cells.

A simple mathematical model of DSB distributions in DNA from irradiated interphase eukaryotic cells is considered and an approximate description of resulting DNA sedimentation profiles is derived. The model takes into account the differences found between the radiosensitivities of heterochromatin and euchromatin and is based, contrary to the usual approach, on a non-homogeneous distribution of DSB in eukaryotic DNA. Comparison with some experimental DNA sedimentation profiles prefers the proposed model to the common one. At the same time a greater radiosensitivity difference (at least in yeast cells for the present) has been established in anoxic conditions compared to aerobic ones.

Cells↗
PubMed1979

NSD and cell survival.

The relation between the NSD concept and cell survival in fractionated irradiation is established; the slope of Strandquist's lines is related to the shape of survival curves for the given type of cells and radiation. A new parameter, CBE, derived from TDF for determining cumulative biological effect is proposed.

Cell Survival↗