Chromosome Aberrations Induced in Human Lymphocytes by 16·5 MeV Protons

Summary

In a track segment irradiation experiment with 16·5 MeV protons the induction of dicentrics was studied in human T-lymphocytes. The dose—response relationship was linear quadratic with estimated parameters α = (0·44 ± 0·07) × 10⁻¹ Gy⁻¹ and β = (1·95 ± 0·30) × 10⁻² Gy⁻². With respect to X-rays a limiting RBE of 1·1–1·2 exists. The present findings are compared with data from other laboratories obtained with 4·9 and 8·7 MeV protons. It was found that the data do not fit theoretical predictions on a proportional relationship between α values and LET. Using the microdosimetric quantity y¯_D (25 nm), the dose average of the lineal energy, for characterization of these proton radiations, at a relevant site diameter of 25 nm the ratio of y¯_D = 1·15 is in accordance only with the observed α ratio of 1·0 ± 0·23 for 8·7 and 16·5 MeV protons. In contrast to the prediction of a constant β at low LET values, the quadratic coefficients increase with increasing LET between 3 and 8 keV/μm.