Chromosome aberration frequencies in human lymphocytes irradiated in a multi-layer array by protons with different LET

Abstract

Purpose : To provide data on the dose-and linear energy transfer (LET)-dependence of the production of dicentrics in human lymphocytes. Materials and methods : Track segment irradiation with 16.5 MeV protons was performed in a multi-layer array allowing the simultaneous exposure of human peripheral lymphocytes in three successive samples. Within these samples the dose-averaged linear energy transfer (L D) of protons increased with increasing depth, i.e. L D = 3.5, 5.3 and 19.0 keV/ mu m. Dicentrics were scored in first division solid-stained metaphases. Results : Dicentric yields measured in the first and second samples fit the linear-quadratic model, those of the third sample fit a linear model of the dose-response relationship. Relative to 137Cs gamma -rays, limiting RBE values of 2.9, 4.3 and 21.5 were determined from the ratios of the respective linear coefficients of the dose-effect curves. The linear dose-effect coefficient increases approximately proportionally with increasing LET. The quadratic coefficient is approximately constant for protons with L D of 3.5 and 5.3 keV/ mu m, and is not significantly different from zero at L D = 19.0 keV/ mu m. Conclusion : This result is well in line with theoretical predictions on the variations of dose-effect coefficients with radiation quality. However, such an evaluation can only be obtained from clearly defined track segment experiments.