Partners and International Organizations
(English)
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Gray Laboratory Cancer Research Trust, Northwood, London, National Centre for Scientific Research 'Demokritos', Athen, Georg-August-Universität, Göttingen, Istituto Nazionali di Legnaro, Istituto Superiore di Sanità, Roma, Rijksuniversiteit, Leiden, Justus-Liebig-Universität, Giessen, Uppsala Universitet, Stockholms Universitet
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Abstract
(English)
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The aim of the EDICAR project was to provide experimental data which are useful for the development of mechanistic models of radiation carcinogenesis. The contribution of the PSI group was to study the cellular response of low-dose exposure to charged particles up to the ultimate low-dose limit, that of a single particle traversal of a cell. These studies made use of the irradiation technique developed within framework programme 3 which includes exposure of a large number of individual cells to low energy light ions (protons, a-particles) and the measurement of the position of particle traversals through cell nuclei with an accuracy of less than 1 mm. The technique enables the study of selected cellular endpoints depending on the number of particle traversals and of the energy deposited in the cell nucleus. The aim of the PSI group was (i) to extend preliminary investigations of cell survival to other cell lines that are commonly used to detect DNA damage and chromosomal aberrations (e.g. CHO-K1) and to use different LET's, (ii) to investigate the influence of the repair-ability of DNA double-strand breaks using a repair-deficient cell line (XR-V15B) and (iii) to examine the difference between survival measured by conventional irradiation and that of measured track irradiation of individual cells.
Chinese hamster ovary cells (CHO-K1), Chinese hamster fibroblast parental cells (V79, V79B) and mutant cells (V15B) were irradiated with a-particles at LET's of 89 and ~130 keV/mm. Surviving fractions were plotted as function of the individual dose deposited in the cell nuclei. CHO and V15B cells were found to be more radiosensitive than V79 and V79B cells, and the effectiveness of a-particles per unit dose was measured to be higher at 89 keV/mm than at ~130 keV/mtm. The conventional radiosensitivities were found to be 2 to 3 times smaller than the individual ones. Cell survival declined exponentially in the dose range up to 0.6 Gy. Survival measured at ~130 keV/mtm deviated from the exponential dose dependence and dropped to less than one third of its former value in the dose interval between 0.65 and 0.75 Gy. However at 89 keV/~un no significant deviation from the exponential decrease was observed. The repair-deficient cell line V15B exhibits the expected distinctly higher radiosensitivity than its parental line V79B. The radiosensitivity of V79 cells measured in this study at ~130 keV/mtm corresponds with data found in the literature. On the other hand the sensitivity obtained for CHO cells is higher than published by Raju et al., Radiat. Res. 133, 289 (1993). The observed higher radiosensitivity at 89 keV/mm agrees with findings of other studies which report a maximum RBE for doubly charged particles at about 90-100 keV/mm. The observed deviation from a pure exponential decline of survival as function of the deposited individual dose cannot be explained. At the moment, no systematical or methodological error can be relied to it. Additional studies with a-particles of lower LET would be needed to investigate this behaviour.
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