Luminosity-independent measurement of the proton-proton total cross section at √s=8 TeV.

The TOTEM collaboration has measured the proton-proton total cross section at √s=8 TeV using a luminosity-independent method. In LHC fills with dedicated beam optics, the Roman pots have been inserted very close to the beam allowing the detection of ~90% of the nuclear elastic scattering events. Simultaneously the inelastic scattering rate has been measured by the T1 and T2 telescopes. By applying the optical theorem, the total proton-proton cross section of (101.7±2.9) mb has been determined, well in agreement with the extrapolation from lower energies. This method also allows one to derive the luminosity-independent elastic and inelastic cross sections: σ(el)=(27.1±1.4) mb; σ(inel)=(74.7±1.7) mb.

Double diffractive cross-section measurement in the forward region at the LHC.

The first double diffractive cross-section measurement in the very forward region has been carried out by the TOTEM experiment at the LHC with a center-of-mass energy of sqrt[s]=7 TeV. By utilizing the very forward TOTEM tracking detectors T1 and T2, which extend up to |η|=6.5, a clean sample of double diffractive pp events was extracted. From these events, we determined the cross section σDD=(116±25) µb for events where both diffractive systems have 4.7<|η|min<6.5.

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.

Inactivation of individual cells by divers ions at different LET values.

A new formula linking the shape of survival curve to the inactivation probabilities after different numbers of cell hits has been derived. It has been used in analyzing recent experimental data obtained with monolayer cells irradiated at definite values of LET (in different parts of Bragg peaks). The new approach allows not only deriving the values of inactivation probabilities at given LET values; unexpected consequences seem to follow especially for inactivation characteristics of carbon ions in different parts of the Bragg peak, too.

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.

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.

Application of a semi-phenomenological model to experimental data of radiation induced pneumopathy in pigs.

A semi-phenomenological model has been derived, which describes the inactivation effect on individual cells by survival curves. This model is applied to experimental data of pneumopathy in pigs. The corresponding survival curves as well as the relations between cell survival and complication probability are calculated and discussed. Furthermore, dose-response curves for single dose irradiation and different fractionation schemes are derived. The comparison between the response curve for single dose irradiation and similar curves from the literature shows a good agreement.

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.

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.

A model of DSB-repair kinetics.

A model of repair kinetics of DSB based on a step-by-step removal of individual double-strand breaks inside an autonomous repair unit is proposed and compared with the alternative model commonly used in modelling repair kinetics, which is based on an assumption of stochastic removal of cellular lesions. The former model seems to be preferred by the recently published experimental data displaying the time decrease of average DSB number per cell in irradiated Saccharomyces cerevisiae (strain 211 B) held in non-growth conditions.

A new concept of cumulative biological effect.

The basis of the NSD concept is systematically reviewed and compared with that used in derivation of a new factor describing a cumulative biological effect (CBE) at the end of a fractionated irradiation. It is shown that some basic assumptions used in derivation of NSD and TDF factors cannot be fulfilled. The new CBE factor is free of this deficiency; it can be useful especially for studying biological effects of different irradiation beams.

Strandquist's graphs and the new mathematical formula for cumulative biological effect.

The new formula for cumulative biological effect (CBE) derived on the basis of main characteristics of Strandquist's graphs has been used for an analysis of experimental fractionation data. Some new aspects concerning fractionated irradiation have been mentioned.

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.