PubMed Health⌕ Search

Biomedical subjects

R Wideröe

Publications and source records attributed to R Wideröe.

12 recordsLinked to original sources
PubMed1990

[2-component theory and radiation therapy].

The two-component theory which describes the biological effect of X-ray and particle irradiation divides radiation into densely ionizing radiation (ion density in water greater than four ions per 100 A, i.e. LET greater than 12 keV/microns) and loosely ionizing radiation with low ion densities. In case of densely ionizing radiation, the ions can produce breaks of both cords of DNA thus causing the death of the cell (alpha effect). Lower ion densities will produce only slight damages which are possibly lethal but can be partly repaired (beta effect). If the cell parameters are known (L. Cohen 1983), the number of surviving cells after an irradiation can be calculated. The surviving lung cells and tumor cells (squamous cell carcinoma) have been calculated for a pulmonary irradiation with 30 MeV electrons and 200 keV X-rays (single doses of 2 and 5 Gy), respectively. The electron irradiation with single doses of 5 Gy turned out to be the most favorable therapy sparing the greatest number of lung cells and reducing the tumor cells in the most effective way (down to 1.6 x 10(-10)).

Carcinoma, Squamous Cell↗
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↗
PubMed1979

Remarks about fractionation schemes.

Today a change from the orthodox "200 rad daily, 5 times per week" scheme to other improved treatment schemes is in the foreground of discussions. However, the situation is very complex and so far no distinct solution has been found. Radiobiology has recommended larger doses at less frequent intervals, but also smaller doses given more often have been used with quite good results. Several factors are important: Tumor conditions, dimensions, growth and sensitivity--reoxygenation of hypoxic tumor cells--recovery and tolerance of normal cells and, last but not least, the general state of the patient. To explain and unravel the problems an example of therapy with high-energy electrons is described. Considering four fundamental successively depending decisions an empirical system is described which may enable us to find improved treatment schemes. Finally a method is explained which makes it possible to transform a treatment scheme to a different equivalent scheme by calculating a total effective standard dose (ESD). This calculation follows exactly the isoeffect principle and makes possible a comparison of different treatment schemes using also different types of radiation.

Electrons↗
PubMed1978

[Theories on radiobiological effects (author's transl)].

Radiobiology has revealed two entirely different effects on irradiated cells. An early, interphase, death (alpha-effect) and also sublethal and potential lethal damage causing mitotic abnormalities leading to a delayed death (beta-effect). The alpha-effect, caused by relative great ion densities, is now interpreted as a double break of the DNA molecule in the cell nucleus. The beta-effect, caused by smaller ion densities might be due to adjacent single breaks of the DNA. The nonlinear dose dependent of the beta-effect can be explained by rapid repair processe having a limited repair capacity. Slow repair of damaged normal cells in G1-phase can be enhanced by medical means and this might be important for clinical radiotherapy.

Animals↗
PubMed1977

[Electron therapy].

The limited range of electrons yields depth doses and dose distributions offering the possibility to spare the tissue situated behind the tumor and to deliver a smaller volume dose. Electrons, therefore, can produce dose distributions being more favorable than those to be obtained with X-rays. The general radiation responses to electronic treatment are feeble. Clinical experiences also have shown that electrons are doing less harm to normal tissues than do X-rays. This may be derived from more important beta-effects and lesser alpha-effects of the electronic irradiation. The normal cells have a capacity for repair following beta-lesions which surpasses that of tumor cells, and thus, the electivity of electronic irradiation will increase and the clinical results are being explained. Schumacher (Berlin) has developed an improved fractionation schedule for electrons, using higher single doses once a week. The new schedule diminishes the number of tumor cells much more effectively than the conventional scheme utilized until now, and brings about, moreover, an additional protection of normal cells. Reoxygenation of anoxic tumor cells is sponsored. The clinical results from the new schedule (4262 cases) are very good.

Electrons↗
PubMed1976

[Biomedical use and dosimetry of pions of the sin 590 MeV isochrone cyclotrone. VII. Radiation therapy using negative pions (author's transl)].

The scheme of radiation of Schumacher for high energy electrons is investigated. In it 3 high individual doses are given at first. In the second phase which follows immediately, weekly single doses of 500 rad are given until the tumor is completely destroyed. Reoxygenation and transformation of anoxic cells are important here for the number of surviving tumor cells but unfortunately still rather unknown. This uncertainty can be removed with the Pion therapy in which transformation does not take a large part. About 10 single doses of negative pions of 150-200 rad should be clearly superior to 5000 rad electron doses (D1 = 500 rad) and should not exceed the limits of tolerance with a weekly treatment. Finally the importance of contamination with electrons of the pionrays is examined. Exact measurement of this contamination is necessary.

Bronchial Neoplasms↗
PubMed1976

[Tumor inactivation and radiobiology].

In this paper, the inactivation of tumors and the tolerance of irradiated surrounding normal tissues is considered under radiobiological aspects. Surviving euoxic cells may be calculated by means of a simple exponential function being characterized by a reduction constant D0. This constant decreases with increasing single doses. Another exponential function allows the calculation of the probability of tumor destruction from the surviving fraction of tumor cells after irradiation. Examples show the probability curves steeply rising with the total dose, in accordance with former observations of Holthusen (S-curves). From the amount of total dose and the steepnees of the rise the values of radiation sensitivity of the particular cells may be evaluated. If there is a fraction of anoxic tumor cells, it is probable that after every irradiation a part of them is transformed into euoxic cells. In such a case, the recovery curves, depending on the degree of reoxygenation, will shift to larger values of the total doses. A good reoxygenation, therefore, is highly important for the success of the irradiation, it can be realized by appropriate irradiation programs. The regeneration (repopulation) of normal cells is of fundamental importance for the restitution of normal tissues following radiation injury. It is generally assumed that the tolerance dose is reached when the number of surviving normal cells arrives at a lower limit. Cohen's measurements at the skin of patients treated with 200 keV X-rays have been used for the calculation of tolerance doses for Co-60 gamma-rays and fast electrons. The tolerance doses depend on the amount of the single doses and result in calculated values of over 10000 rd with electron irradiation of 500 rd per week. These calculations are confirmed by the findings of Schumacher with electron irradiation.

Cobalt Radioisotopes↗
PubMed1975

Remarks on oxygen effects.

Oxygen concentration will influence the alpha- and beta-effect (two-component theory of radiation effects) independently. The beta-effect is reduced by a dose-modifying factor gamma. Oxygen, in competition with enzyme repair actions fortifies a part of the beta-lesions and this model leads to a simple equation for the factor gamma. The alpha-effect is also enhanced by oxygen. Measurements of OER indicate that the reduction of the effect from aerobic to anoxic condition might be about 70%. The functional dependence of oxygen concentration has not been investigated. For small oxygen concentrations of 0.15 to 0.5 muM/l and doses below 1000 R Révész and Littbrand have found that oxygen can protect the irradiated cells and thus increase survivals with about 10%. This is explained as a scavenger action where radical hydrogen atoms are oxidized and hydrated electrons captured by oxygen moelcules. When the oxygen concentration is increased, or with higher doses, the usual sensitizing effect of oxygen exceeds the protection effect. The influence of oxygen on alpha-effects are mainly connected with indirect radiation effects and thus depend on temperature and milieu.

Cell Survival↗
PubMed1975

Cellular survival and isoeffect formulae: a study in applied radiobiology.

The Ellis formula for the sterilization of tumors is compared with isoeffect curves for sterilizing doses as a function of the fractionation number N. Using cell parameters from human kidney cells irradiated in cell cultures we get a good agreement over a wide range of N values. The exponents obtained from the calculations are 0,26-0,30 and 0,36 for 200 keV X-rays, Co-60 rays and high energy electrons respectively. A reduction of tumor cells to 10(-8) seems sufficient for tumor sterilization. For normal tissue Ellis has proposed another formula (for X-rays) where a time factor T0,11 concerns homeostatic repair and proliferation of normal alls. The Ellis formula can be simplified when we assume that all treatment schemes be given with the same weekly dose-rate, i.e. have the same "hardness". Cell survivals according to this formula have been calculated and tolerance doses for other radiations giving the same effect computed. Only for electrons do the tolerance doses exceed the sterilizing doses. The Ellis formula does not represent isoeffects and can only be regarded as an approximation. Tolerance doses can be calculated giving the same cell survivals for all N-values, i.e. isoeffects, and a comparison with sterilizing doses shows a good agreement with clinical experience. However, the influence of the overall-dose rate still is an unsolved problem which can only be solved experimentally.

Cell Survival↗
PubMed1975

Problems and trends in radiotherapeutic treatment of deep-seated tumors.

The heterogeneous structure of tumors is described and the importance of oxygen is explained and analyzed. Three ways of solving the clinical problems of anoxic tumor cells are today being tried. Hyperbaric oxygen breathing before and during irradiation; using fast neutrons and thirdly the use of improved treatment schemes with low LET (i.e. low alpha-value) radiation. The various methods are described and critically evaluated. Calculations are made with the two-component model of radiation. The improved treatment schemes seem in most cases to work well and to solve the problem. If necessary, for certain radio-resistant tumors the normal treatment might also be supplemented by other methods.

Alpha Particles↗