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Chromosome aberration frequencies in human lymphocytes irradiated in a multi-layer array by protons with different
1GSF, National Research Center for Environment and Health, Institute of Radiobiology, Neuherberg, Germany.
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 (LD) of protons increased with increasing depth, i.e. LD = 3.5, 5.3 and 19.0 keV/microm. 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 LD of 3.5 and 5.3 keV/microm, and is not significantly different from zero at LD= 19.0 keV/microm.
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.