Radiation research
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We have observed that when a single linear-quadratic (LQ) function is used to fit the radiation survival response of an asynchronously dividing population of V79 cells, a consistent misfit occurs at low doses. The data can be better described by fitting the low-dose and high-dose ranges separately, and there is evidence of a two-component response. The most obvious explanation is that we may simply be seeing the response of subpopulations of cells of different radiosensitivity: sensitive G1-, G2- and M-phase cells and resistant S-phase cells. ⋯ The best fit, however, was obtained using a two-population LQ model, which suggested approximately equal numbers of sensitive and resistant cells. When the survival response of tightly synchronized G1/S-phase cells was measured using the cell sorting assay, no substructure was observed. This offers strong support to the hypothesis that the substructure observed in the asynchronous survival response is due to subpopulations of cells of different, cycle-dependent radiosensitivity.
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The concept of intrinsic radiosensitivity is now strongly associated with the linear-quadratic (LQ) model which is currently the best and the most reliable method to fit the first three decades of a survival curve for both human fibroblast and human tumor cell lines. This approach has led to the major conclusions that it is the initial part, and not the distal part, of the survival curve which truly characterizes intrinsic cellular radiosensitivity and there is a correlation between the parameters describing mainly the initial part of the survival curve (alpha, SF2, D) and the clinical radioresponsiveness. More accurate analysis with flow cytometry or a dynamic microscopic image processing scanner (DMIPS) has allowed further study of the survival curve which has shown two sorts of substructure. ⋯ However, it may be important to bear in mind the possible extra effect of low doses outside the target volume if regions in the vicinity are subsequently retreated. Concerning clinical radiation-induced carcinogenesis, three studies described a higher relative risk associated with small doses per fraction or very low dose rate. The results and the interpretation of these studies are discussed.
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Precursor frequencies of cytotoxic lymphocytes to autologous Epstein-Barr virus-transformed B cells and serum titers of anti-Epstein-Barr virus-related antibodies were measured in 68 atomic bomb survivors to clarify the immune mechanism controlling Epstein-Barr virus infection. The precursor frequency was negatively correlated with the titer of anti-early antigen IgG, which is probably produced at the stage of viral reactivation. ⋯ These results suggest that T-cell memory specific to Epstein-Barr virus keeps the virus under control and that the precursor frequency assay is useful for the evaluation of immune responses to Epstein-Barr virus. However, no significant effect of atomic bomb radiation on the precursor frequency was observed in the present study, probably due to the limited number of participants.