[en] Hypoxic hamster cells were treated with gamma radiation and hyperthermia with and without the addition of nitroimidazoles. In one series of experiments the effect of combining Ro-07-0582 and cysteamine was studied. Graphs are presented to show survival data for cells exposed for various periods of time at four different temperatures to Ro-07-0582. The presence of the nitroimidazole sensitized the hypoxic cells to a point where their sensitivity approached that of aerated cells. The OER was 2.5 for a drug concentration of 5 mM. The cytotoxic and radiosensitizing properties of the nitroimidazole were almost completely reversed by cysteamine

[en] The aim of this work is to determine the thermal defect, i.e., the fraction of absorbed radiation energy that is not converted to heat in the absorber, for samples of A-150 tissue-equivalent plastic obtained from different laboratories and molded under different conditions, and to examine the dependence of the thermal defect on the energy and type of the irradiation particles. This information is needed to utilize this plastic for calorimetric neutron dosimetry. Density and chemical composition of plastic disks were determined, and initial tests of the measuring equipment were made. Further improvements are anticipated before measurements are begun. 3 tables

[en] Cells of fibroblastic origin were grown in Petri dishes and dishes were x-irradiated after plating cells at a density such that about 400 viable cells per dish survived the various treatments. Results of single dose experiments showed that survival, as a function of dose above 200 rads, decreased exponentially. The transformation frequency increased rapidly from 10 to 400 rads and then reached a plateau from 600 to 1000 rads. In a split dose experiment the transformation frequency increased rapidly from 300 to 400 rads and then decreased slowly

[en] Pregnant hamsters were exposed to 300 rad of x rays at 12 days of gestation and the embryos were removed 30 min later. Cell cultures were prepared and transformed cells were identified by altered morphology and growth patterns. Observations were made on chromosome number, fibrinolytic activity of transformed cells, release of macrophage inhibitory factor, the pattern of cellular lysosomal hydrolases, and the ganglioside content of cells. The transformed cells gave rise to tumors in syngeneic hamsters

[en] Experimental procedures and data analysis of a microdosimetry run using two sphere-within-a-sphere-type wall-less proportional counters are described. ⁴⁰Ar beams of 450 MeV/A were used. Microdensimetric distributions are shown for several regions of the Bragg curve. The presence of wall effects is noted. 6 figures, 5 tables

[en] Survival curves are shown for two cell cycle times and for irradiations at atmospheric pressure and 70 torr pressure using single deuteron ions of 33 keV/μm. The data for late S phase cells coincide for the two pressure regimes but the G1-to-S transition curves are displaced such that the survival at reduced pressure is greater. The reduced pressure resulted in higher survival for the G1-to-S transition cells using single ion irradiation with 20 keV/μm particles. The lack of a reduced pressure effect on late S cells using 33 keV/μm particle irradiation was consistent with the lack of effect found for asynchronous cells that were x-irradiated

[en] In an ongoing experiment, mammalian cells are exposed to pairs of correlated deuterons resulting from the break-up of accelerated deuteron molecules. The purpose is to obtain further information on the question how the microscopic distribution of energy affects the irradiated cell. By varying the average spacing of the correlated deuterons, patterns of microscopic energy distribution are obtained which are characteristically different from those in conventional experiments, where the LET of the radiation is varied. The study deals with the microdosimetry of the molecular beam experment and with the possible inferences that can be drawn if the dependence of the cellular effect on the mean spacing of the deuterons is obtained

[en] Radiation-induced sublesions are repaired as a function of time, with the number of sublesions decreasing with time. The probability that sublesions will interact with others produced later will depend on the repair rate. Thus predictions of the dual radiation theory depend on the rate of production of sublesions, and hence on dose rates. A simultaneous fit to five levels of excess tumors is plotted against the irradiation period. The fit is very good. The value for X² is only 2.74 for as many as 28 data points, corresponding to a total of 21 degrees of freedom. Thus, the analysis strongly favors the dual radiation theory

[en] Radiobiological measurements were made on the 80 MeV d⁺ → Be beam. Biological test systems included growth inhibition of Vicia seedlings under aerated and hypoxic conditions and determination of survival curves of Chinese hamster cells under aerated and hypoxic conditions. Results showed no indication of decreasing OER with increasing neutron energy

[en] A review of progress on preparations for a complex and detailed series of experiments designed to explore the microdosimetric characteristics of the energetic heavy ions available at the BEVALAC Biomedical Facility is given. The essence of the proposed experiment is twofold: (1) to measure microdosimetric spectra with a wall-less counter in a container large enough so that wall effects are essentially eliminated, and (2) to measure these spectra as a function of the distance of closest approach of the ion to the counter, i.e., the impact parameter. The first point will resolve the question of wall-effect perturbations on the spectra, while the second point will yield detailed experimental evidence concerning the relative importance of the delta ray, or ''indirect'' contribution to the biological effect of these heavy ions. At the same time, it may be possible to explore the contribution of fragmentation products to the total y-spectra