Showing papers in "Radiation and Environmental Biophysics in 1979"

Radiation induced chromosome aberrations and the Poisson distribution.

Abstract: Data on the distribution of dicentrics and acentrics observed when human lymphocytes are cultured for 48 h after irradiation by X-rays,γ-rays, and neutrons are presented. Analysis shows that for dicentrics, the observed distribution for X-rays,γ-rays, and fission neutrons may be described by Poisson statistics but for higher energy neutrons overdispersion is observed. The phenomenon of overdispersion is also observed for acentrics irrespective of the radiation used. The possibility that overdispersion results from the variations of dose in sensitive sites leads to the conclusion that for dicentrics the site size is considerably larger than the 1–2 µm diameter derived by applying the dual action theory to the dose effect relationships. This larger site may well be the cell nucleus.

Radioprotection by DMSO of mammalian cells exposed to X-rays and to heavy charged-particle beams.

Abstract: Populations of G1-phase Chinese hamster cells in stirred suspensions containing various concentrations of DMSO were irradiated with 250 kV X-rays or various heavy charged-particle beams. Chemical radioprotection of cell inactivation was observed for all LET values studied. When cell survival data were resolved into linear and quadratic components, the extent and concentration dependence of DMSO protection were found to be different for the two mechanisms. The chemical kinetics of radioprotection for single-events were similar for LET values up to those which gave the maximum RBE. DMSO protected to a lesser extent against energetic argon ions at an median LET of ∼ 220 keV/µm. These data could indicate the contribution of indirect action by hydroxyl radicals and hydrogen atoms to cell inactivation by single-hit and double-hit mechanisms for various radiation qualities. The decrease in RBE observed at very high LET may result, in part, from reduced yields of water radicals at 10−9−10−8 s resulting from radical recombination mechanisms within the charged particle tracks.

Interaction of radiofrequency and microwave radiation with living systems. A review of mechanisms.

Abstract: Human health aspects and biological effects of radio frequency (RF) and microwave radiation have been in the focus of research efforts in the last decade. An understanding of the interaction mechanisms between such radiation and living systems is essential in interpreting experimental results and assessing potential health hazards.

The direct influence of electromagnetic fields on nerve- and muscle cells of man within the frequency range of 1 Hz to 30 MHz

Abstract: By using several biophysical approximations and considering man as free space model limiting order-of-magnitude values for external electric and magnetic field strengths which may be hazardous for human beings were calculated. Danger may occur by excitation processes below 30 kHz for field strengths exceeding these limiting values; for frequencies larger than 60 kHz, thermal effects are predominant before excitation occurs. The external electric field strength necessary for causing action potentials in the central nervous system exceeds by far the corona forming level. But excitation is possible by strong alternating magnetic fields. Furthermore, by comparing the electrically and magnetically induced currents with the naturally flowing currents in man caused by the brain's and heart's electrical activity, a "lower boundary-line" was estimated. Regarding electric or magnetic field strengths undercutting this boundary-line, direct effects on the central nervous system may be excluded. Other mechanisms should be responsible for demonstrated biological effects.

Effects of modulated RF energy on the EEG of mammalian brains. Effects of acute and chronic irradiations.

Abstract: The effects of modulated radio frequency fields on mammalian EEGs were investigated using acute and chronic irradiations at non-thermal level. The EEG signals were computer processed to obtain power spectra. Rabbits were exposed to the field for 2 h a day for 6 weeks at 1–10 MHz (15 Hz modulation) at the level of 0.5–1 kV/M. Silver electrodes placed on the skull surface were used for recording of the EEG. Usually they were removed immediately after initial recordings of the EEG and reinserted before the final and intermediate EEG recordings. With this arrangement, modulated RF fields produced a change in EEG patterns by enhancing the low frequency components and decreasing high frequency activities. On the other hand, acute irradiations did not produce noticeable changes in the EEG at the level of 0.5–1 kV/M (1–30 MHz, 60 Hz modulation) as long as the use of intracranial electrodes was avoided.

Distribution of radiation induced lesions in human chromosomes and dose-effect relation analysed with G-banding.

Abstract: Human female lymphocytes were exposed to X-rays in vitro at 7 different doses between 40–280 R. In 830 metaphases chromosome analyses were carried out with either conventional staining or G-banding, respectively. 486 breakpoints are non-randomly distributed between chromosomes and chromosome arms. An excess of lesions was present in chromosomes 1 and 5 or in lp. 85% of the lesions were located in G-negative bands (pale G-bands). 29% of all lesions appeared in either the last terminal pale band (21%) or in the centromere region (8%). With regard to an application of G-banding for a biological dose-estimation, the dose-response relations of dic and ace were analysed. Although G-banding enables detailed analysis of the whole karyotype it cannot be recommended for cytogenetic routine analyses in medical radioprotection monitoring, without suitable automated scoring techniques. Dose estimations based on the frequency of dic and carried out with conventional staining cannot be essentially improved at present with banding. Nevertheless, by banding criteria for a correct evaluation of other aberration types, e.g. ace, can be provided. This is a prerequisite for the calculation of representative dose-effect curves.

The role of microdosimetry in radiobiology.

Abstract: Microdosimetry is a branch of radiological physics that provides quantitative characterization of the non-uniformity of energy deposition in uniformly irradiated matter. Considerations based on microdosimetry indicate that the action of ionizing radiation on the cells of higher organisms depends on the square of the specific energy absorbed in subcellular volumes. This is the basis of the Theory of Dual Radiation Action. The basic postulate of this theory is reviewed and four factors are discussed that modify its elementary formulation.

Oxygen isotope fractionation during respiration for different temperatures of T. utilis and E. coli K12.

Abstract: The temperature dependence of the oxygen isotope fractionation factor during respiration has been examined for two different microorganisms, namelyTorulopsis utilis andEscherichia coli K12 representing a yeast and a bacterium, respectively. The investigation covered a temperature range of 18° C, that is from 16° C to 34° C forT. utilis and from 19° C to 37° C forE. coli K12. Within this temperature range the fractionation factor ofT. utilis increases by 0.18‰; an insignificant change (Δδ 10° C = 0.063‰;r = 0.067), whereas withE. coli K 12 an increase of 1.12‰; has been observed (Δδ 10° C = 0.6‰;r = 0.55).

Effect of elevated temperatures on the radiation sensitivity of yeast cells of different species.

Abstract: The influence of hyperthermia on the survival of irradiated yeast cells of different species has been studied The experiments reported in the paper have shown: (1) simultaneous action of ionizing radiation and high temperatures appeared to increase the radiation response by a factor of approximately 27 for diploid and only by a factor of 15 for haploid cells of wild-type; (2) the combined action of high temperature and ionizing radiation had no synergistic effect for rad51 mutant diploid yeast cells; (3) heating before or after irradiation did not alter the radiation response of yeast cells; (4) enhancement of yeast cell sensitivity by simultaneous action of hyperthermia and 239Pu-alpha-particles was negligible; (5) the magnitude and the rate of liquid holding recovery is lowered with increasing of irradiation temperature On this basis, it was concluded that possible mechanism for thermal sensitization of yeast cells may involve the reduced capacity of cells to recover damages resulted from the combined action of both modalities

Development of the therapy planning programs for the 60 beams SIN pion applicator.

Abstract: The present status of the therapy planning programs for the SIN pion applicator is presented.

Therapy planning and dosimetry for the pion applicator at the Swiss Institute for Nuclear Research (SIN).

Abstract: At the Swiss Institute for Nuclear Research a 60 beam pion applicator for radiotherapy is under construction. The methods to produce homogeneous dose distributions in arbitrarily shaped volumes is presented, together with details on the activities in therapy planning and dosimetry in view of the use of the applicator for patients.

The effect of environmental temperature and average dose rate of microwave radiation on the oxygen-consumption rate of mice.

Abstract: The oxygen consumption rate of CF1 male mice was determined before, during, and after sham- and microwave-irradiation at environmental temperatures of 20° C, 24° C, 30° C, and 35° C, relative humidity of 55%, and air flow rate of 78 ml/min. Five forward power levels ranging from 0.09 to 3.3 W, which resulted in corresponding average dose rates ranging from 1.2 to 45.1 mW/g were used. The values of the oxygen consumption rate were converted to those of the specific metabolic rate (SMR). The result indicates that with high levels of microwave dosing (greater than 10 mW/g) the specific metabolic rate of mice decreased in some cases, in the environmental temperatures of 20° C and 24° C. However, the decreased SMR values were not lower than the SMR values of the sham-irradiated group in 30° C. In the case of 35° C, the high level dosing with microwave radiation caused increases in the SMR value over the sham value. A possible trend towards increased SMR value during and after irradiation with low level (1.6 mW/g) microwave radiation in the environmental temperatures of 24° C and 30° C suggests further experiments with low level microwave radiation to determine possible effects of low level microwave radiation in stimulating increases in specific metabolic rate.

Rate constants studies of the dye-sensitized photoinactivation of lysozyme.

Abstract: The rate constants for the photodynamic inactivation of hen egg-white lysozyme at different temperatures were studied. Arrhenius plots of the methylene blue sensitized photo-inactivation of lysozyme gave an experimental activation energy of 7.5 kcal/mol. The rate constants for the photodynamic inactivation of lysozyme in the presence of riboflavin decreased almost linearly in the temperature range 4–38° C. The photosensitized oxidation of lysozyme at −20° C in freezing and non-freezing solvents was possible only in the presence of riboflavin. The effect of dye concentration on the quantum yield and rate constant for the photodynamic inactivation of lysozyme was examined. The quantum yields were lower when the concentrations of methylene blue used were low, and increased on increasing dye concentration, getting to a maximum and then declined at higher dye concentrations. It was found that in the case of riboflavin sensitized photo-inactivation of lysozyme both the rate constant and the quantum yield increased as the dye concentration increased. No maximum was observed over the range of dye concentrations studied. A new mechanism is postulated for the photodynamic action of lysozyme in the presence of riboflavin.

[The action of hyperthermia on DNA repair (author's transl)].

Abstract: The time-course of DNA repair afterβ irradiation was measured in HeLa cells at various temperatures. Unscheduled DNA synthesis was estimated by incorporation of3H-thymidine in presence of hydroxyurea. To dedect the ligase reaction, the number of single strand breaks (SSB) was determined by centrifugation in alcaline sucrose as well as by hydroxylapatite chromatography after partial denaturation. In addition, the temperature dependence of DNA polymerase and DNase reaction in cell-free systems were measured. These data were compared with the reduction of colony-forming ability of the cells caused byβ irradiation and following repair at various temperatures. All steps of repair proceed faster at 41–43° than at 37° but cells are most resistant toβ irradiation at 37°. We therefore assume that the DNA repair process at 42° is faster but more error prone than at 37°.

Cell survival over the depth profile after irradiation with a negative pion beam.

Abstract: The colony-forming ability of Chinese hamster fibroblast cells in vitro has been investigated throughout the depth dose profile of a negative pion beam In the peak and 2 cm beyond, the RBE for macroclones (more than 50 cells per clone) was 13 and in the plateau region 08--10 All of the microclones (2-49 cells per clone) were observed as well The RBE values are the same for peak and somewhat higher for plateau and post peak than found in cell survival studies referring to macroclones

Energy deposition spectra of negative pions and their application to radiation therapy.

Abstract: Treatment planning for pion radiation therapy must take into account changes in radiation quality within the patient. At the biomedical channelπE3 of SIN (Swiss Institute for Nuclear Research) microdosimetric measurements have been performed to investigate radiation quality within pion irradiated phantoms. Results are presented in terms of microdosimetric spectra and derived quantities. As expected marked differences are observed between dose peak and plateau for “narrow” pion beams. The influence of simulated site diameter on measured spectra has been found to be more pronounced in the plateau region than in the peak. Investigation of the influence of peak width on radiation quality revealed a dilution of the high-LET dose fraction for broader peaks.

Low-dose effects of X-rays and negative pions on the pronuclear zygote stage of mouse embryos.

Abstract: Mouse embryos in the pronuclear-zygote stage (day 0 of gestation) were irradiated with 13.5 rad of 140 kV X-rays or negative pions. On day 13 the fetuses were examined for developmental anomalies such as intrauterine death, growth retardation and malformations. Significant decreases in the percentage of normal implantations were obtained with peak pions (high LET) and X-rays, whereas the effect of plateau pions was less obvious. Irradiation with peak pions was more effective than with X-rays by a factor of about 1.7.

Quantitative risk in radiation protection standards.

Abstract: Although the overall aim of radiobiology is to understand the biological effects of radiation, it also has the implied practical purpose of developing rational measures for the control of radiation exposure in man. The emphasis in this presentation is to show that the enormous effort expended over the years to develop quantitative dose-effect relations relationships in biochemical and cellular systems, animals and human beings, now seems to be paying off. The pieces appear to be falling into place, and a framework is evolving to utilize these data. Specifically, quantitative risk assessments will be discussed in terms of the cellular, animal and human data on which they are based; their use in the development of radiation protection standards; and their present and potential impact and meaning in relation to the quantity dose equivalent and its special unit, the rem. Recent neutron carcinogenesis data in man are evaluated.

Effect of239Pu on mouse hemopoietic stem cells in different types of bone marrow cavities

Abstract: Repopulative activity of hemopoietic stem cells of mice given i.v. 5 kBq239Pu/mouse (166.5 kBq/kg) was followed. The activity retained was measured in the whole mouse, the skeleton and the liver. Simultaneously average cumulative skeletal dose was calculated. Quantitative parameters of the stem cell compartment and the marrow cellularity were studied in variously arranged bones (femur, pelvis, lumbar vertebra) using the exocolonizing test and cytological techniques. The effects of radiation were most marked in lumbar vertebra, less serious changes were found in pelvis and only a moderate response was present in femur. The bone marrow hemopoiesis is damaged in various bone sites to different degrees and the percentage of cells at risk appears higher in trabecular than in cortical bone.

Effect of negative pions, relative to 140 kV -- 29 MeV photons and 20 MeV electrons, on proliferation of Ehrlich ascites carcinoma cells.

Abstract: The effect of negative pions (peak and plateau), photons (140 kV and 29 MeV), and 20 MeV electrons on the proliferative capacity of Ehrlich ascites carcinoma cells was investigated. Proliferative survival curves plotted for the modalities employed are presented. Under the experimental conditions used, the peak pions were more effective than plateau pions by a factor of about 1.4. For 50% survival, 140 kV X-rays had the same effect as peak pions but the latter was more effective (factor 1.2) at 10% survival level. When 140 kV X-rays were taken as the standard, following are the RBE values calculated at 50% survival level: plateau pions -0.73; peak pions -about 1.0; 29 MeV photons -0.73 and 20 MeV electrons -0.6. The results obtained are compared with those reported on other tumor systems and biological test objects.

Influence of the DNA structure on the free radical induction due to proflavine and light treatment.

Abstract: Induction of peroxide free radicals (detected by Electron Paramagnetic Resonance at 77 K) due to the photodynamic activity of proflavine was measured on bacteriophage ∅X174 DNA either single-stranded (ss) as isolated from the virion, or double-stranded supercoiled (RFI) as isolated from the infected bacteria. Comparison was made with calf thymus DNA photosensitization.

Tube growth stimulation of pine pollen by low doses of irradiation. Dose rate, reproducibility and comparison between UV-light and ionizing rays.

Abstract: Stimulation of the tube growth of pine pollen by low doses of UV-light or X-rays is a reproducible process, but it depends strongly of the dose rate applied. It can be proved that the observed effect is more determined by dose rate and irradiation time than by the dose itself which can vary by nearly one order of magnitude for achieving the same increase in tube elongation. The range of absorbed energy at which the stimulation effect can be observed is rather broad and overlapping between UV and X-rays. In the average the UV-energy needed is 5 times higher than X-ray energy.

Preclinical radiobiology with pions: RBE--values for mouse skin damage as a function of single doses of pions.

Abstract: The macroscopic reaction of the mouse skin was used to derive RBE values for negativeπ-Mesons. Hind limbs of mice were irradiated with pions or X-rays. The pions were produced by the 590 MeV accelerator of the Schweizerisches Institut fur Nuklearforschung (SIN). Early skin reaction was assessed over a period of 6–30 days after irradiation with single doses (20–45 Gy). The radiation damage was scored using an arbitrary scale of effect. The time pattern of development of the skin reaction and the subsequent healing after exposure both to pions and X-rays were similar, indicating that depletion and repopulation of the basal cells of the skin were comparable, both after pions and X-rays. RBE values as a function of pion doses at the peak (dose maximum), plateau and at the postpeak (12 mm downstream of the dose maximum) were computed with nonparametric statistical methods. The RBE at the peak and at the plateau relative to X-rays of the same dose rate was 1.15–1.25 and 0.85, respectively. The RBE of peak pions manifested a marked dependence on dose, when plateau pions were chosen as reference radiation. In this experiment there was no significant difference in RBE between peak and postpeak. The importance of some experimental condition (dose rate, irradiation volume) is discussed.

Changes in production, yield, and chemical composition of corn(Zea mays) after ultrasound treatments of the seeds

Abstract: In the spring of each year (1972–1974) air-dry grains of two inbred lines ofZ. mays (7275-13-1 and 106) were exposed for 17 h to a low level (25 kHz) of ultrasound and subsequently planted in the field together with untreated controls and grown to maturity. In the fall of each year the ears of each group were harvested and the number of broken stalks, the yield and weight of grains and grain parts and the alcohol-soluble amino acid complement of the grain parts were determined. Broken stalks and yields were unaffected, however the embryos from the treated groups retained more moisture than their respective controls, dry weights were also significantly increased. The alcohol-soluble amino acid composition of the embryos was markedly changed, levels of proline were severely depressed in the embryos of both lines and generally increased in the endosperms. Sonication resulted in an overall decrease of up to 40% in totalled alcohol-soluble amino acids in the grains of 7275-13-1.

Effect of negative pi mesons on vascular permeability of brain in neonatal rats.

Abstract: Neonatal rats and their radiation-induced cerebral petechial hemorrhages were used as an experimental system for evaluating the effects of negative pions on healthy tissue and especially on the microvasculature. Dose response curves for peak and plateau pions (dose range 150--250 rad and 100--400 rad, respectively) were obtained and compared with those of 200 kV X-rays of corresponding dose rates. The RBE of the peak pions was 1.1, that of the plateau pions 0.6 resulting in a peak/plateau ratio of 1.8. Implications were made as to the importance of this favorable peak/plateau relationship since the response of the capillary endothelium to pion-irradiation might be one of the limiting factors in radiotherapy.

Application of the thermoluminescent dosimetry to a pion beam.

Abstract: The thermoluminescent dosimetry is currently applied to radiation therapy in order to measure dose distributions on phantoms or to control the dose in vivo for special procedures or critical organs. The application of this method to the SIN's (Switzerland) pion beam has been studied.

Pre-clinical studies of the negative pi-meson beam at TRIUMF.

Abstract: Theπ− flux from the biomedical channel at TRIUMF increases with increasing channel momentum, while the contaminating electron flux decreases. Since the electrons appear to result from conversion of the high energyγ-rays produced byπ0 decay in the production target, the electron contamination can be reduced further by target configurations which minimize gamma conversion.

Radiobiological data for clinical dosimetry in pion tumour therapy

Abstract: Ehrlich ascites tumour cells were irradiated with negative pions at different positions in the plateau and the peak of the depth absorbed dose curve. Dose-survival curves for immediate testing of the viability of the cells are given and are compared with other types of radiations in use for therapy. From the data obtained after repair of potentially lethal damage effective survival curves for fractionated irradiation are evaluated.

Measurements at the piE3 single beam correlated to dosimetry and therapy-planning for the pion applicator at SIN.

Abstract: Using ionization chambers, aluminium activation, TLD and scintillation counters 3-dimensional total dose-distributions, stardose-distributions and pion stop-distributions have been measured in a single pion beam for various momenta and momentum spreads. It is demonstrated how these data will be used as an input into the therapy-planning program. The techniques developed are suited to check dynamical treatment with 60 pion beams.

Contrasting oxygen-effects in the inactivation of ribonuclease A by N.3, (SCN).-2 and .OH radicals.

Abstract: N 3 ⋅ exhibits higher efficiency than⋅OH in the inactivation of RNase in de-acerated (neutral) aqueous solution. In O2-saturated solution the⋅OH-induced inactivation is enhanced, but N 3 ⋅ and (SCN) 2 ⋅ − become remarkably inefficient. Our results suggest that semi-oxidized tyrosine, the predominant initial defect induced by N 3 ⋅ and (SCN) 2 ⋅ − but not by⋅OH, can be re-reduced upon reaction with O 2 ⋅ − or cysteine.