[The low dose and low dose rate cytogenetic effects induced by gamma-radiation in human blood lymphocytes in vitro. I. the results of physical and dosimetric study].

Physical and dosimetric characteristics of the gamma-radiation field which is formed in the room containing the 60Co radiation source were investigated on condition of an unclosed breech mechanism and the presence of the lead layer on the beam pathway. The inverse square law was approximately found for the dependence of the dose rate vs distance on the radiation source both for the unclosed breech mechanism and lead layer (4 and 9 cm wide) in the beam pathway. This finding indicated a non-significant contribution of the radiation scattered from the walls at the point of cytogenetic experiments. The Monte Carlo calculations showed that some changes in the efficient spectrum of gamma-radiation resulted in a decreased average energy of 60Co gamma-rays to 1.03, 1.17 and 1.07 MeV for the unclosed breech mechanism, behind 4 and 9 cm lead layers, respectively.

[The low dose and low dose rate cytogenetic effects induced by gamma-radiation in human blood lymphocytes in vitro. II. the results of cytogenetic study].

The yield of chromosome aberrations induced by gamma-radiation of 60Co in human blood lymphocytes in vitro at low doses (30 divided by 600 mGy) and low dose rates (0.70, 5.05, 59.2 mGy/min) was investigated. It was found that the observed level of chromosomal aberrations induced by gamma-irradiation was unaffected by the value of the dose rate when using constant dose rate and obtaining different doses by altering the exposure time. However, a relatively enhanced level of chromatid aberrations was found at 5.05 and 59.2 mGy/min dose rates in the dose range less than 250 mGy. We have found that the observed level of the sum of chromosomal aberrations induced by gamma-irradiation at doses less than 250 mGy and a dose rate of 59.2 mGy/min was essentially larger compared with the level extrapolated from high doses (above 300 mGy) using a linear-quadratic dose curve. This complied with our previous finding in 1976, 1977 when the enhanced level of dicentrics was only found at a high dose rate approximately 500 mGy/min. Such a non-linear cytogenetic effect does not manifest itself statistically significantly at dose rates of 0.70 and 5.05 mGy/min for the sum of chromosomal aberrations and does not manifest itself at all for dicentrics at all the examined dose rates.

[Study of dose-rate effects of neutron radiation in a wild-type and a repair-deficient yeasts saccharomyces].

We report here a comparative analysis of RBE for lethality of a single pulse (duration 65 micros) of fast neutron with ultra high dose rates (up to 6 x 10(6) Gy/s) and continuous neutron radiation (3.6 x 10(3) s) of the pulse reactor BARS-6. Three diploid strains, one haploid strain and three diploid repair-deficient strains (rad52-1/rad52-1; rad54/rad54; rad2/rad2) were used. The RBE values (D(0gamma)/1D(0n)) of a single pulse and continuous neutron irradiation were equal (1.7-1.8) with maximum RBE (4.1-3.1) in region of low doses (shoulder region). Haploid cells were found to be more (3 times) sensitive to both gamma-rays and neutrons than the wild type. There was no obvious decrease in the RBE of 1.9 in highly sensitive haploid cells as compared with highly resistant diploid cells. The repair-deficient strains (rad52-1/rad52-1; rad54/rad54) were more (up to 10 fold) sensitive to both neutrons and gamma-rays as compared with their parent line. The RBE values of 1.5-1.7 of neutrons for these mutants (independent by of the mode of irradiation) were found. The repair-deficient mutant rad2/rad2 had similar sensitivity as a wild type and a RBE value was 2.0. We have concluded that biological effectiveness of the neutrons of pulse reactor BARS-6 was independent of the dose-rate, differing up to 10(8) fold. The RBE didn't vary significantly with the capacity of cells to repair DNA damages.

[Effect of temperature on the development of chromosome aberrations in human blood lymphocytes irradiated in pulse and continuous modes at BARS-6 reactor].

Summarized results of 5 repeated experiments of comparative study of radiation effects of the pulse reactor BARS-6 either in a single pulse or a continuos irradiation mode on human lymphocytes are presented. Higher efficiency (30-40%) of continuous irradiation (exposure duration 1 h) rather than pulse irradiation with ultra-high dose rates (1-2.5) x 10(6) Gy/min (pulse duration 65 micros) was confirmed. The efficiency ratio did not depend on the temperature, 20 degrees C or 0 degrees C, during the exposure. Cell repair system and chromatin conformation influence on the results obtained is discussed.

[Cytogenetic effect of the pulse reactor BARS-6 continuous or one-time irradiation with ultrahigh dose rate on human lymphocytes].

The results of the comparative study of radiation effects of the pulse reactor BARS-6 either in single pulse or continuos irradiation mode on human G0 lymphocytes are presented. Under identical doses the cytogenetic efficiency was observed to be higher for continuous irradiation (1 hour) than for single pulse irradiation with ultrahigh dose rate (0.5-3) x 106 Gy/minutes (pulse duration 65 x 10(-6) s). The difference averaged about 37% on total aberration frequency and 27% on the sum of dicentrics and centric rings. The influence of the dose rate and of the mixed gamma-neutron irradiation on the obtained results is discussed.

[Biological effectiveness of pulsed and continuous neutron radiation for Saccharomyces yeast cells]. / Biologicheskaia éffektivnost' impul'snogo i nepreryvnogo neitronnogo izlucheniia dlia kletok drozhzhei Saccharomyces.

The article presents the data on biological effectiveness of neutrons generated by the pulsed reactor BARS-6 (dose-rate up to 6 x 10(6) Gy/s) in comparison with fast neutrons of the reactor BR-10 (dose-rate 6.3 x 10(-2) Gy/s). It was shown for yeast cells of a wild type that the RBE values of pulsed neutrons varied insignificantly with a dose (2.0-1.7) white for continuous neutron irradiation clear RBE dependence on the dose was observed. It was also found that the yeast cells had identical capability of postirradiation recovery in non-nutrient medium (LHR) following both gamma-irradiation and neutron exposure irrespective of neutron dose-rate.

[Physico-technological standards of remote neutron radiotherapy and quality assurance (literature review)]. / Fiziko-tekhnicheskie aspekty garantii kachestva neitronnoi distantsionnoi luchevoi terapii i problemy eë obespecheniia (obzor literatury)

Issues in physico-technological support of remote neutron therapy are discussed. On the basis of evaluation of the literature, conclusion is made that a number of important problems are still to be solved.

[The results of the cytogenetic examination of children and adolescents living in radionuclide-contaminated regions of Kaluga Province]. / Rezul'taty tsitogeneticheskogo obsledovaniia detei i podrostkov, prozhivaiushchikh v zagriaznennykh radionuklidami raionakh Kaluzhskoi oblasti.

After the Chernobyl accident in a period from 1989 to 1992 blood samples were collected and analysed for chromosomal aberrations in lymphocytes from 490 children born and living continuously in two districts of Kaluga Province with radioactive contamination. The results of cytogenetic examinations show the frequency of unstable aberrations in children from Zhizdra District to be higher than that in children from Ulyanovo District and in the control group. No correlation was found between the thyroid absorbed doses ranging from 0 to 5 Gy and the aberration frequencies. No differences in chromosomal aberration yields were observed in children born before or after the Chernobyl accident. Repeat examinations of the same children cohorts revealed no significant changes with time in the level of unstable aberrations.

[The depth distribution of neutron-capture events in 10B nuclei during the irradiation of a water phantom with neutrons from the channels of the BR-10 reactor]. / Glubinnoe raspredelenie neitron-zakhvatnykh sobytii na iadrakh 10B pri obluchenii vodnogo fantoma neitronami iz kanalov reaktora BR-10.

The authors present the results of experimental investigations of distribution of capture events on nuclei 10B by the depth of a water phantom during its irradiation with beams T-4 and B-3 of the BR-10 reactor. A ferrous sulfate dosimeter with added boric acid was used as a detector of such events. The depth of a water phantom on which the effect of boron capture by a neutron beam is decreased 2-fold, is 1.7 cm. For the B-3 beam a curve of depth correlation of neutron capture events had a broad maximum at a depth of 4-5 cm.

[Influence of the dose rate and postradiation hyperthermia on the cytogenetic effect of irradiation of cells in the G0 stage by 252Cf and 60Co sources]. / Vliianie moshchnosti dozy i postradiatsionnoi gipertermii na tsitogeneticheskii éffekt pri obluchenii kletok v stadii G0 istochnikami 252Cf i 60Co.

The paper is concerned with the results of a comparative study of radiation injury of chromosomes of human lymphocytes at the G0 stage resulting from the influence of 60Co gamma quanta and high activity 252Cf radiation sources and depending on a dose and dose rate; with the potentialities of modifying a cytogenetic effect of irradiation by postradiation hyperthermia of cells. It has been shown that at the G0 stage of a cell cycle the frequency of chromosome aberrations does not depend on the dose rate of 252Cf radiation within the range of 0.0035-0.35 Gy/min. by the neutron component. Linear correlation between the frequency of induced chromosome aberrations and a dose was observed within a dose range of 0.27-3.1 Gy. Thus, a conclusion is that postradiation hyperthermia at the G0 stage does not almost influence the frequency of chromosome aberrations during 252Cf radiation, and increases it insignificantly during 60Co gamma-radiation.

[Chromosome aberrations and reproductive death of mammalian cells. Quantitative relations between these effects]. / Khromosomnye aberratsii i reproduktivnaia gibel' kletok mlekopitaiushchikh. Kolichestvennye sootnosheniia mezhdu étimi éffektami.

The data reported in the literature concerning the relationship between the yield of chromosome aberrations and the number of cells without aberrations, on the one hand, and the survival rate of mammalian cells, on the other, with a reference to different types of radiation are reviewed in this article. It is shown that the number of chromosome aberrations per one lethal damage, as to the results obtained by different authors, ranges from 0.5 to 1.5, this discrepancy is mainly due to different methods applied by different authors, and at least one chromosome aberration corresponds to a lethal damage caused by irradiation in the G1 phase.

[Relative biological effectiveness of highly active mixed gamma-neutron 252Cf radiation]. / Otnositel'naia biologicheskaia éffektivnost' smeshannogo gamma-neitronnogo izlucheniia 252Cf vysokoi aktivnosti.

Comprehensive radiobiological studies of the relative biological and genetic efficacy (RBE and RGE) of powerful 252Cf radiation (the ANET-B unit) were conducted using research tools of various radiosensitivity (bacteria, Drosophila, Chinese hamster cells, murine thymocytes, human and murine bone marrow stem cells, human peripheral blood lymphocytes, Lewis lung carcinoma cells). It was shown in the tests of reproductive or interphase death and chromosome aberrations that the RBE and the RGE values of a 252Cf new source varied within the same limits from 1.3 to 3.0 whereas in the tests of gene mutations the RGE of the source did not exceed the efficacy of 60Co gamma-radiation and in some cases it was much lower. Thus the RBE of the new source in induced lethal and chromosome damages was 2-4 times lower than the efficacy of a low-activity 252Cf source used now in radiotherapy.